draft-ietf-mobileip-ipv6-05.txt   draft-ietf-mobileip-ipv6-06.txt 
IETF Mobile IP Working Group David B. Johnson IETF Mobile IP Working Group David B. Johnson
INTERNET-DRAFT Carnegie Mellon University INTERNET-DRAFT Carnegie Mellon University
Charles Perkins Charles Perkins
Sun Microsystems Sun Microsystems
13 March 1998 4 August 1998
Mobility Support in IPv6 Mobility Support in IPv6
<draft-ietf-mobileip-ipv6-05.txt> <draft-ietf-mobileip-ipv6-06.txt>
Status of This Memo Status of This Memo
This document is a submission by the Mobile IP Working Group of the This document is a submission by the Mobile IP Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted Internet Engineering Task Force (IETF). Comments should be submitted
to the Working Group mailing list at "mobile-ip@SmallWorks.COM". to the Working Group mailing list at "mobile-ip@SmallWorks.COM".
Distribution of this memo is unlimited. Distribution of this memo is unlimited.
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at and may be updated, replaced, or obsoleted by other documents at
any time. It is inappropriate to use Internet-Drafts as reference any time. It is inappropriate to use Internet-Drafts as reference
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To view the entire list of current Internet-Drafts, please check To view the entire list of current Internet-Drafts, please check
the "1id-abstracts.txt" listing contained in the Internet-Drafts the "1id-abstracts.txt" listing contained in the Internet-Drafts
Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Europe), Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au
ftp.isi.edu (US West Coast). (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu
(US West Coast).
Abstract Abstract
This document specifies the operation of mobile computers using IPv6. This document specifies the operation of mobile computers using IPv6.
Each mobile node is always identified by its home address, regardless Each mobile node is always identified by its home address, regardless
of its current point of attachment to the Internet. While situated of its current point of attachment to the Internet. While situated
away from its home, a mobile node is also associated with a care-of away from its home, a mobile node is also associated with a care-of
address, which provides information about the mobile node's current address, which provides information about the mobile node's current
location. IPv6 packets addressed to a mobile node's home address are location. IPv6 packets addressed to a mobile node's home address are
transparently routed to its care-of address. The protocol enables transparently routed to its care-of address. The protocol enables
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Contents Contents
Status of This Memo i Status of This Memo i
Abstract i Abstract i
1. Introduction 1 1. Introduction 1
2. Comparison with Mobile IP for IPv4 3 2. Comparison with Mobile IP for IPv4 3
3. Terminology 4 3. Terminology 6
3.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 4 3.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Mobile IPv6 Terms . . . . . . . . . . . . . . . . . . . . 5 3.2. Mobile IPv6 Terms . . . . . . . . . . . . . . . . . . . . 7
3.3. Specification Language . . . . . . . . . . . . . . . . . 6 3.3. Specification Language . . . . . . . . . . . . . . . . . 8
4. Overview of Mobile IPv6 7 4. Overview of Mobile IPv6 9
4.1. Basic Operation . . . . . . . . . . . . . . . . . . . . . 7 4.1. Basic Operation . . . . . . . . . . . . . . . . . . . . . 9
4.2. New IPv6 Destination Options . . . . . . . . . . . . . . 9 4.2. New IPv6 Destination Options . . . . . . . . . . . . . . 11
4.3. Conceptual Data Structures . . . . . . . . . . . . . . . 11 4.3. Conceptual Data Structures . . . . . . . . . . . . . . . 13
4.4. Binding Management . . . . . . . . . . . . . . . . . . . 14 4.4. Binding Management . . . . . . . . . . . . . . . . . . . 16
5. New IPv6 Destination Options 16 5. New IPv6 Destination Options 19
5.1. Binding Update Option Format . . . . . . . . . . . . . . 16 5.1. Binding Update Option Format . . . . . . . . . . . . . . 19
5.2. Binding Acknowledgement Option Format . . . . . . . . . . 20 5.2. Binding Acknowledgement Option Format . . . . . . . . . . 23
5.3. Binding Request Option Format . . . . . . . . . . . . . . 24 5.3. Binding Request Option Format . . . . . . . . . . . . . . 27
5.4. Home Address Option Format . . . . . . . . . . . . . . . 25 5.4. Home Address Option Format . . . . . . . . . . . . . . . 28
6. Modifications to IPv6 Neighbor Discovery 27 6. Modifications to IPv6 Neighbor Discovery 30
6.1. Router Advertisement Message Format . . . . . . . . . . . 27 6.1. Modified Router Advertisement Message Format . . . . . . 30
6.2. Advertisement Interval Option Format . . . . . . . . . . 28 6.2. Modified Prefix Information Option Format . . . . . . . . 31
6.3. Changes to MinRtrAdvInterval Limits . . . . . . . . . . . 29 6.3. New Advertisement Interval Option Format . . . . . . . . 33
6.4. New Home Agent Information Option Format . . . . . . . . 34
6.5. Changes to Sending Router Advertisements . . . . . . . . 36
6.6. Changes to Sending Router Solicitations . . . . . . . . . 37
7. Requirements for IPv6 Nodes 30 7. Requirements for IPv6 Nodes 39
7.1. Requirements for All IPv6 Hosts and Routers . . . . . . . 30 7.1. Requirements for All IPv6 Hosts and Routers . . . . . . . 39
7.2. Requirements for IPv6 Home Agents . . . . . . . . . . . . 30 7.2. Requirements for All IPv6 Routers . . . . . . . . . . . . 39
7.3. Requirements for IPv6 Mobile Nodes . . . . . . . . . . . 31 7.3. Requirements for IPv6 Home Agents . . . . . . . . . . . . 39
7.4. Requirements for IPv6 Mobile Nodes . . . . . . . . . . . 40
8. Correspondent Node Operation 32 8. Correspondent Node Operation 42
8.1. Receiving Packets from a Mobile Node . . . . . . . . . . 32 8.1. Receiving Packets from a Mobile Node . . . . . . . . . . 42
8.2. Receiving Binding Updates . . . . . . . . . . . . . . . . 32 8.2. Receiving Binding Updates . . . . . . . . . . . . . . . . 42
8.3. Requests to Cache a Binding . . . . . . . . . . . . . . . 33 8.3. Requests to Cache a Binding . . . . . . . . . . . . . . . 43
8.4. Requests to Delete a Binding . . . . . . . . . . . . . . 34 8.4. Requests to Delete a Binding . . . . . . . . . . . . . . 44
8.5. Sending Binding Acknowledgements . . . . . . . . . . . . 34 8.5. Sending Binding Acknowledgements . . . . . . . . . . . . 44
8.6. Sending Binding Requests . . . . . . . . . . . . . . . . 34 8.6. Sending Binding Requests . . . . . . . . . . . . . . . . 45
8.7. Cache Replacement Policy . . . . . . . . . . . . . . . . 35 8.7. Cache Replacement Policy . . . . . . . . . . . . . . . . 45
8.8. Receiving ICMP Error Messages . . . . . . . . . . . . . . 36 8.8. Receiving ICMP Error Messages . . . . . . . . . . . . . . 46
8.9. Sending Packets to a Mobile Node . . . . . . . . . . . . 37 8.9. Sending Packets to a Mobile Node . . . . . . . . . . . . 47
9. Home Agent Operation 39 9. Home Agent Operation 49
9.1. Receiving Router Advertisement Messages . . . . . . . . . 39 9.1. Receiving Router Advertisement Messages . . . . . . . . . 49
9.2. Dynamic Home Agent Address Discovery . . . . . . . . . . 39 9.2. Dynamic Home Agent Address Discovery . . . . . . . . . . 50
9.3. Primary Care-of Address Registration . . . . . . . . . . 40 9.3. Primary Care-of Address Registration . . . . . . . . . . 51
9.4. Primary Care-of Address De-registration . . . . . . . . . 43 9.4. Primary Care-of Address De-registration . . . . . . . . . 54
9.5. Tunneling Intercepted Packets to a Mobile Node . . . . . 44 9.5. Intercepting Packets for a Mobile Node . . . . . . . . . 54
9.6. Renumbering the Home Subnet . . . . . . . . . . . . . . . 44 9.6. Tunneling Intercepted Packets to a Mobile Node . . . . . 56
9.7. Renumbering the Home Subnet . . . . . . . . . . . . . . . 57
10. Mobile Node Operation 46 10. Mobile Node Operation 60
10.1. Sending Packets While Away from Home . . . . . . . . . . 46 10.1. Sending Packets While Away from Home . . . . . . . . . . 60
10.2. Movement Detection . . . . . . . . . . . . . . . . . . . 48 10.2. Receiving Packets While Away from Home . . . . . . . . . 62
10.3. Forming New Care-of Addresses . . . . . . . . . . . . . . 50 10.3. Movement Detection . . . . . . . . . . . . . . . . . . . 63
10.4. Sending Binding Updates to the Home Agent . . . . . . . . 51 10.4. Forming New Care-of Addresses . . . . . . . . . . . . . . 66
10.5. Sending Binding Updates to Correspondent Nodes . . . . . 53 10.5. Sending Binding Updates to the Home Agent . . . . . . . . 67
10.6. Sending Binding Updates to the Previous Default Router . 55 10.6. Dynamic Home Agent Address Discovery . . . . . . . . . . 68
10.7. Retransmitting Binding Updates . . . . . . . . . . . . . 55 10.7. Sending Binding Updates to Correspondent Nodes . . . . . 69
10.8. Rate Limiting for Sending Binding Updates . . . . . . . . 56 10.8. Sending Binding Updates to the Previous Default Router . 71
10.9. Receiving ICMP Error Messages . . . . . . . . . . . . . . 56 10.9. Retransmitting Binding Updates . . . . . . . . . . . . . 72
10.10. Receiving Binding Acknowledgements . . . . . . . . . . . 57 10.10. Rate Limiting for Sending Binding Updates . . . . . . . . 72
10.11. Receiving Binding Requests . . . . . . . . . . . . . . . 58 10.11. Receiving Binding Acknowledgements . . . . . . . . . . . 72
10.12. Using Multiple Care-of Addresses . . . . . . . . . . . . 58 10.12. Receiving Binding Requests . . . . . . . . . . . . . . . 73
10.13. Routing Multicast Packets . . . . . . . . . . . . . . . . 58 10.13. Receiving ICMP Error Messages . . . . . . . . . . . . . . 74
10.14. Returning Home . . . . . . . . . . . . . . . . . . . . . 59 10.14. Receiving Tunneled Router Advertisements . . . . . . . . 74
10.15. Using Multiple Care-of Addresses . . . . . . . . . . . . 75
10.16. Routing Multicast Packets . . . . . . . . . . . . . . . . 76
10.17. Returning Home . . . . . . . . . . . . . . . . . . . . . 76
11. Constants 61 11. Constants 78
12. IANA Considerations 62 12. IANA Considerations 79
13. Security Considerations 63 13. Security Considerations 80
13.1. Binding Updates, Acknowledgements, and Requests . . . . . 63 13.1. Binding Updates, Acknowledgements, and Requests . . . . . 80
13.2. Home Address Options . . . . . . . . . . . . . . . . . . 63 13.2. Home Address Option . . . . . . . . . . . . . . . . . . . 80
13.3. General Mobile Computing Issues . . . . . . . . . . . . . 64 13.3. General Mobile Computing Issues . . . . . . . . . . . . . 81
Changes from Previous Draft 66 Changes from Previous Draft 83
Acknowledgements 68 Acknowledgements 85
References 69 References 86
Chair's Address 71 Chair's Address 88
Authors' Addresses 72 Authors' Addresses 89
1. Introduction 1. Introduction
This document specifies the operation of mobile computers using This document specifies the operation of mobile computers using
Internet Protocol Version 6 (IPv6) [5]. Without specific support Internet Protocol Version 6 (IPv6) [5]. Without specific support
for mobility in IPv6, packets destined to a mobile node (host or for mobility in IPv6, packets destined to a mobile node (host or
router) would not be able to reach it while the mobile node is away router) would not be able to reach it while the mobile node is away
from its home link (the link on which its home IPv6 subnet prefix is from its home link (the link on which its home IPv6 subnet prefix is
in use), since routing is based on the subnet prefix in a packet's in use), since routing is based on the subnet prefix in a packet's
destination IP address. In order to continue communication in spite destination IP address. In order to continue communication in spite
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beyond the scope of this document. beyond the scope of this document.
The protocol specified in this document solves the problem of The protocol specified in this document solves the problem of
transparently routing packets to and from mobile nodes while away transparently routing packets to and from mobile nodes while away
from home. However, it does not attempt to solve all general from home. However, it does not attempt to solve all general
problems related to the use of mobile computers or wireless networks. problems related to the use of mobile computers or wireless networks.
In particular, this protocol does not attempt to solve: In particular, this protocol does not attempt to solve:
- Handling links with partial reachability, such as typical - Handling links with partial reachability, such as typical
wireless networks. Some aspects of this problem are addressed wireless networks. Some aspects of this problem are addressed
by the movement detection procedure described in Section 10.2, by the movement detection procedure described in Section 10.3,
but no attempt has been made to fully solve this problem in its but no attempt has been made to fully solve this problem in its
general form. Most aspects of this problem can be solved by the general form. Most aspects of this problem can be solved by the
workaround of restricting such networks to only one router per workaround of restricting such networks to only one router per
link, although there are still possible hidden terminal problems link, although there are still possible hidden terminal problems
when two nodes on the same link (on opposite sides of the router) when two nodes on the same link (on opposite sides of the router)
attempt to communicate directly. attempt to communicate directly.
- Access control on a link being visited by a mobile node. This - Access control on a link being visited by a mobile node. This
is a general problem any time an untrusted node is allowed is a general problem any time an untrusted node is allowed
to connect to any link layer. It is independent whether the to connect to any link layer. It is independent whether the
connecting node uses Mobile IP, DHCP [2], or just "borrows" an IP connecting node uses Mobile IP, DHCP [2], or just "borrows" an IP
address on the link. address on the link.
2. Comparison with Mobile IP for IPv4 2. Comparison with Mobile IP for IPv4
[This section will include a comparison between the Mobile IPv6 The design of Mobile IP support in IPv6 (Mobile IPv6) represents a
protocol and the Mobile IPv4 protocol [13, 12, 14]. However, this natural combination of the experiences gained from the development
comparison has not yet been written. It will be filled in with the of Mobile IP support in IPv4 (Mobile IPv4) [15, 14, 16], together
next revision to this draft.] with the opportunities provided by the design and deployment of a new
version of IP itself (IPv6) and the new protocol features offered
by IPv6. Mobile IPv6 thus shares many features with Mobile IPv4,
but the protocol is now fully integrated into IP and provides many
improvements over Mobile IPv4. This section summarizes the major
differences between Mobile IPv4 and Mobile IPv6:
- Support for what is known in Mobile IPv4 as "Route
Optimization" [17] is now built in as a fundamental part
of the protocol, rather than being added on as a optional
set of extensions that may not be supported by all nodes
as in Mobile IPv4. This integration of Route Optimization
functionality allows direct routing from any correspondent node
to any mobile node, without needing to pass through the mobile
node's home network and be forwarded by its home agent, and thus
eliminates the problem of "triangle routing" present in the base
Mobile IPv4 protocol [15]. This integration also allows the
Mobile IPv4 "registration" functionality and the Mobile IPv4
Route Optimization functionality to be performed by a single
protocol rather than two separate (and different) protocols.
- Support is also integrated into Mobile IPv6 -- and into IPv6
itself -- for allowing mobile nodes and Mobile IP to coexist
efficiently with routers that perform "ingress filtering" [6]. A
mobile node now uses its care-of address as the Source Address in
the IP header of packets it sends, allowing the packets to pass
normally through ingress filtering routers. The home address
of the mobile node is carried in the packet in a Home Address
destination option, allowing the use of the care-of address in
the packet to be transparent above the IP layer. The ability
to correctly process a Home Address option in a received packet
is required in all IPv6 nodes, whether mobile nor stationary,
whether host or router.
- The use of the care-of address as the Source Address in each
packet's IP header also simplifies routing of multicast packets
sent by a mobile node. With Mobile IPv4, the mobile node
had to tunnel multicast packets to its home agent in order to
transparently use its home address as the source of the multicast
packets. With Mobile IPv6, the use of the Home Address option
allows the home address to be used but still be compatible with
multicast routing that is based in part on the packet's Source
Address.
- There is no longer any need to deploy special routers as
"foreign agents" as are used in Mobile IPv4. In Mobile IPv6,
mobile nodes make use of the enhanced features of IPv6, such
as Neighbor Discovery [13] and Address Autoconfiguration [22],
to operate in any location away from home without any special
support required from its local router.
- Unlike Mobile IPv4, Mobile IPv6 utilizes IPsec [8, 9, 10] for
all security requirements (sender authentication, data integrity
protection, and replay protection) for Binding Updates (which
serve the role of both registration and Route Optimization in
Mobile IPv4). Mobile IPv4 relies on its own security mechanisms
for these functions, based on statically configured "mobility
security associations".
- The movement detection mechanism in Mobile IPv6 provides
bidirectional confirmation of a mobile node's ability to
communicate with its default router in its current location
(packets that the router sends are reaching the mobile node, and
packets that the mobile node sends are reaching the router).
This confirmation provides a detection of the "black hole"
situation that may exist in some wireless environments where the
link to the router does not work equally well in both directions,
such as when the mobile node has moved out of good wireless
transmission range from the router. The mobile node may then
attempt to find a new router and begin using a new care-of
address if its link to its current router is not working well.
In contrast, in Mobile IPv4, only the forward direction (packets
from the router are reaching the mobile node) is confirmed,
allowing the black hole condition to persist.
- Most packets sent to a mobile node while away from home in
Mobile IPv6 are tunneled using an IPv6 Routing header rather than
IP encapsulation, whereas Mobile IPv4 must use encapsulation
for all packets. The use of a Routing header requires less
additional header bytes to be added to the packet, reducing the
overhead of Mobile IP packet delivery. To avoid modifying the
packet in flight, however, packets intercepted and tunneled
by a mobile node's home agent in Mobile IPv6 must still use
encapsulation for tunneling.
- While a mobile node is away from home, its home agent intercepts
any packets for the mobile node that arrive at the home network,
using IPv6 Neighbor Discovery [13] rather than ARP [18] as is
used in Mobile IPv4. The use of Neighbor Discovery improves
the robustness of the protocol (e.g., due to the Neighbor
Advertisement "override" bit) and simplifies implementation
of Mobile IP due to the ability to not be concerned with any
particular link layer as is required in ARP.
- The use of IPv6 encapsulation (and the Routing header) removes
the need in Mobile IPv6 to manage "tunnel soft state", which was
required in Mobile IPv4 due to limitations in ICMP for IPv4. Due
to the definition of ICMP for IPv6, the use of tunnel soft state
is no longer required in IPv6 for correctly relaying ICMP error
messages from within the tunnel back to the original sender of
the packet.
- The dynamic home agent address discovery mechanism in Mobile IPv6
uses IPv6 anycast and returns a single reply to the mobile node,
rather than the corresponding Mobile IPv4 mechanism that used
IPv4 directed broadcast and returned a separate reply from each
home agent on the mobile node's home link. The Mobile IPv6
mechanism is more efficient and more reliable, since only
one packet need be sent back to the mobile node and since the
mobile node is less likely to lose one of the replies because no
"implosion" of replies is required by the protocol.
- Mobile IPv6 defines an Advertisement Interval option on
Router Advertisements (equivalent to Agent Advertisements in
Mobile IPv4), allowing a mobile node to decide for itself how
many Router Advertisements (Agent Advertisements) it is willing
to miss before declaring its current router unreachable.
- The use of IPv6 destination options allows all Mobile IPv6
control traffic to be piggybacked on any existing IPv6 packets,
whereas in Mobile IPv4 and its Route Optimization extensions,
separate UDP packets were required for each control message.
3. Terminology 3. Terminology
3.1. General Terms 3.1. General Terms
IP IP
Internet Protocol Version 6 (IPv6). Internet Protocol Version 6 (IPv6).
node node
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A mobile node is always addressable by its home address, whether it A mobile node is always addressable by its home address, whether it
is currently attached to its home link or is away from home. While is currently attached to its home link or is away from home. While
a mobile node is at home, packets addressed to its home address are a mobile node is at home, packets addressed to its home address are
routed to it using conventional Internet routing mechanisms in the routed to it using conventional Internet routing mechanisms in the
same way as if the node were never mobile. Since the subnet prefix same way as if the node were never mobile. Since the subnet prefix
of a mobile node's home address is the subnet prefix (or one of the of a mobile node's home address is the subnet prefix (or one of the
subnet prefixes) on the mobile node's home link (it is the mobile subnet prefixes) on the mobile node's home link (it is the mobile
node's home subnet prefix), packets addressed to it will be routed to node's home subnet prefix), packets addressed to it will be routed to
its home link. its home link.
While a mobile node is attached to some foreign link away from While a mobile node is attached to some foreign link away from home,
home, it is also addressable by one or more care-of addresses, in it is also addressable by one or more care-of addresses, in addition
addition to its home address. A care-of address is an IP address to its home address. A care-of address is an IP address associated
associated with a mobile node while visiting a particular foreign with a mobile node while visiting a particular foreign link. The
link. The subnet prefix of a mobile node's care-of address is the subnet prefix of a mobile node's care-of address is the subnet prefix
subnet prefix (or one of the subnet prefixes) on the foreign link (or one of the subnet prefixes) on the foreign link being visited by
being visited by the mobile node; if the mobile node is connected the mobile node; if the mobile node is connected to this foreign link
to this foreign link while using that care-of address, packets while using that care-of address, packets addressed to this care-of
addressed to this care-of address will be routed to the mobile node address will be routed to the mobile node in its location away from
in its location away from home. The association between a mobile home.
node's home address and care-of address is known as a "binding"
for the mobile node. A mobile node typically acquires its care-of The association between a mobile node's home address and care-of
address through stateless [18] or stateful (e.g., DHCPv6 [2]) address is known as a "binding" for the mobile node. A mobile node
address autoconfiguration, according to the methods of IPv6 Neighbor typically acquires its care-of address through stateless [22] or
Discovery [11]. Other methods of acquiring a care-of address stateful (e.g., DHCPv6 [2]) address autoconfiguration, according
are also possible, but such methods are beyond the scope of this to the methods of IPv6 Neighbor Discovery [13]. Other methods
of acquiring a care-of address are also possible, such as static
pre-assignment by the owner or manager of a particular foreign link,
but details of such other methods are beyond the scope of this
document. document.
While away from home, the mobile node registers one of its bindings While away from home, a mobile node registers one of its care-of
with a router on its home link, requesting this router to function addresses with a router on its home link, requesting this router
as the "home agent" for the mobile node. This binding registration to function as the "home agent" for the mobile node. This binding
is done by the mobile node sending a packet with a "Binding Update" registration is done by the mobile node sending to the home agent
destination option to the home agent; the home agent then replies by a packet containing a "Binding Update" destination option; the
returning a packet containing a "Binding Acknowledgement" destination home agent then replies to the mobile node by returning a packet
option to the mobile node. The care-of address in this binding containing a "Binding Acknowledgement" destination option. The
registered with its home agent is known as the mobile node's "primary care-of address in this binding registered with its home agent is
care-of address". The mobile node's home agent thereafter uses proxy known as the mobile node's "primary care-of address". The mobile
Neighbor Discovery to intercept any IPv6 packets addressed to the node's home agent thereafter uses proxy Neighbor Discovery to
mobile node's home address (or home addresses) on the home link, intercept any IPv6 packets addressed to the mobile node's home
and tunnels each intercepted packet to the mobile node's primary address (or home addresses) on the home link, and tunnels each
care-of address. To tunnel each intercepted packet, the home agent intercepted packet to the mobile node's primary care-of address.
encapsulates the packet using IPv6 encapsulation [4], with the outer To tunnel each intercepted packet, the home agent encapsulates the
IPv6 header addressed to the mobile node's primary care-of address. packet using IPv6 encapsulation [4], with the outer IPv6 header
addressed to the mobile node's primary care-of address.
Section 10.12 discusses the reasons why it may be desirable for Section 10.15 discusses the reasons why it may be desirable for
a mobile node to use more than one care-of address at the same a mobile node to use more than one care-of address at the same
time. However, a mobile node's primary care-of address is distinct time. However, a mobile node's primary care-of address is distinct
among these in that the home agent maintains only a single care-of among these in that the home agent maintains only a single care-of
address registered for each mobile node, and always tunnels a mobile address registered for each mobile node, and always tunnels a mobile
node's packets intercepted from its home link to this mobile node's node's packets intercepted from its home link to this mobile node's
registered primary care-of address. The home agent thus need not registered primary care-of address. The home agent thus need not
implement any policy to determine which of possibly many care-of implement any policy to determine which of possibly many care-of
addresses to which to tunnel each intercepted packet, leaving the addresses to which to tunnel each intercepted packet, leaving the
mobile node entirely in control of this policy by which of its mobile node entirely in control of this policy by which of its
care-of addresses it registers with its home agent. care-of addresses it registers with its home agent.
It is possible that while a mobile node is away from home, some nodes It is possible that while a mobile node is away from home, some nodes
on its home link may be reconfigured, such that the router that was on its home link may be reconfigured, such that the router that was
operating as the mobile node's home agent is replaced by a different operating as the mobile node's home agent is replaced by a different
router serving this role. In this case, the mobile node may not router serving this role. In this case, the mobile node may not
know the IP address of its own home agent. Mobile IPv6 provides a know the IP address of its own home agent. Mobile IPv6 provides a
mechanism, known as "dynamic home agent address discovery", that mechanism, known as "dynamic home agent address discovery", that
allows a mobile node to dynamically discover the IP address of a home allows a mobile node to dynamically discover the IP address of a home
agent on its home link with which it may register its care-of address agent on its home link with which it may register its care-of address
while away from home. The mobile node sends a Binding Update to the while away from home. The mobile node sends a Binding Update to the
"Home-Agents anycast address" for its home subnet prefix and thus "Home-Agents anycast address" for its own home subnet prefix and thus
reaches one of the (possibly many) routers on its home link currently reaches one of the (possibly many) routers on its home link currently
operating as a home agent. This home agent rejects the mobile operating as a home agent. This home agent rejects the mobile
node's Binding Update, but returns in the Binding Acknowledgement node's Binding Update, but returns in the Binding Acknowledgement
in response a list of all home agents on the home link. This list in response a list of all home agents on the home link. This list
of home agents is maintained by each home agent on the home link of home agents is maintained by each home agent on the home link
through use of the Home Agent (H) bit in each home agent's periodic through use of the Home Agent (H) bit in each home agent's periodic
unsolicited multicast Router Advertisements. unsolicited multicast Router Advertisements.
The Binding Update and Binding Acknowledgement destination options, The Binding Update and Binding Acknowledgement destination options,
together with a "Binding Request" destination option, are also used together with a "Binding Request" destination option, are also used
to allow IPv6 nodes communicating with a mobile node, to dynamically to allow IPv6 nodes communicating with a mobile node, to dynamically
learn and cache the mobile node's binding. When sending a packet learn and cache the mobile node's binding. When sending a packet
to any IPv6 destination, a node checks its cached bindings for an to any IPv6 destination, a node checks its cached bindings for an
entry for the packet's destination address. If a cached binding for entry for the packet's destination address. If a cached binding for
this destination address is found, the node uses an IPv6 Routing this destination address is found, the node uses an IPv6 Routing
header [5] (instead of IPv6 encapsulation) to route the packet to header [5] (instead of IPv6 encapsulation) to route the packet to
the mobile node by way of the care-of address indicated in this the mobile node by way of the care-of address indicated in this
binding. If, instead, the sending node has no cached binding for binding. If, instead, the sending node has no cached binding for
this destination address, the node sends the packet normally (with this destination address, the node sends the packet normally (with
no Routing header), and the packet is subsequently intercepted and no Routing header), and the packet is subsequently intercepted and
tunneled by the mobile node's home agent as described above. A node tunneled by the mobile node's home agent as described above. Any
communicating with a mobile node is referred to in this document as a node communicating with a mobile node is referred to in this document
"correspondent node" of the mobile node. as a "correspondent node" of the mobile node, and may itself be
either a stationary node or a mobile node.
Since a Binding Update, Binding Acknowledgement, and Binding Request Since a Binding Update, Binding Acknowledgement, and Binding Request
are each represented in a packet as an IPv6 destination option [5], are each represented in a packet as an IPv6 destination option [5],
they may be included in any IPv6 packet. Any of these options can be they may be included in any IPv6 packet. Any of these options can be
sent in either of two ways: sent in either of two ways:
- A Binding Update, Binding Acknowledgement, or Binding Request can - A Binding Update, Binding Acknowledgement, or Binding Request can
be included within any IPv6 packet carrying any payload such as be included within any IPv6 packet carrying any payload such as
TCP [16] or UDP [15]. TCP [20] or UDP [19].
- A Binding Update, Binding Acknowledgement, or Binding Request can - A Binding Update, Binding Acknowledgement, or Binding Request can
be sent as a separate IPv6 packet containing no payload. In this be sent as a separate IPv6 packet containing no payload. In this
case, the Next Header field in the last extension header in the case, the Next Header field in the last extension header in the
packet is set to the value 59, to indicate "No Next Header" [5]. packet is set to the value 59, to indicate "No Next Header" [5].
Mobile IPv6 also defines one additional IPv6 destination option. Mobile IPv6 also defines one additional IPv6 destination option.
When a mobile node sends a packet while away from home, it will When a mobile node sends a packet while away from home, it will
generally set the Source Address in the packet's IPv6 header to one generally set the Source Address in the packet's IPv6 header to one
of its current care-of addresses, and will also include a "Home of its current care-of addresses, and will also include a "Home
Address" destination option in the packet, giving the mobile node's Address" destination option in the packet, giving the mobile node's
home address. Many routers implement security policies such as home address. Many routers implement security policies such as
"ingress filtering" [6] that do not allow forwarding of packets "ingress filtering" [6] that do not allow forwarding of packets that
that appear to have a Source Address that is not topologically appear to have a Source Address that is not topologically correct.
correct. By using the care-of address as the IPv6 header Source By using the care-of address as the IPv6 header Source Address,
Address, the packet will be able to pass normally through such the packet will be able to pass normally through such routers,
routers, yet ingress filtering rules will still be able to locate yet ingress filtering rules will still be able to locate the true
the true physical source of the packet in the same way as packets topological source of the packet in the same way as packets from
from non-mobile nodes. By also including the Home Address option, non-mobile nodes. By also including the Home Address option in each
the sending mobile node can communicate its home address to the packet, the sending mobile node can communicate its home address to
correspondent node receiving this packet, allowing the use of the the correspondent node receiving this packet, allowing the use of
care-of address to be transparent above the Mobile IPv6 support the care-of address to be transparent above the Mobile IPv6 support
level (e.g., at the transport layer). The inclusion of a Home level (e.g., at the transport layer). The inclusion of a Home
Address option in a packet affects only the correspondent node's Address option in a packet affects only the correspondent node's
receipt of this single packet; no state is created or modified in the receipt of this single packet; no state is created or modified in the
correspondent node as a result of receiving a Home Address option in correspondent node as a result of receiving a Home Address option in
a packet. a packet.
4.2. New IPv6 Destination Options 4.2. New IPv6 Destination Options
As discussed in general in Section 4.1, the following four new IPv6 As discussed in general in Section 4.1, the following four new IPv6
destination options are defined for Mobile IPv6: destination options are defined for Mobile IPv6:
Binding Update Binding Update
A Binding Update option is used by a mobile node to notify A Binding Update option is used by a mobile node to notify
a correspondent node or the mobile node's home agent of a correspondent node or the mobile node's home agent of
its current binding. The Binding Update sent to the mobile its current binding. The Binding Update sent to the mobile
node's home agent to register its primary care-of address is node's home agent to register its primary care-of address is
marked as a "home registration". Any packet that includes a marked as a "home registration". Any packet that includes a
Binding Update option MUST also include either an AH [7] or Binding Update option MUST also include either an AH [8] or
ESP [8] header providing sender authentication, data integrity ESP [9] header providing sender authentication, data integrity
protection, and replay protection. The Binding Update option protection, and replay protection. The Binding Update option
is described in detail in Section 5.1. is described in detail in Section 5.1.
Binding Acknowledgement Binding Acknowledgement
A Binding Acknowledgement option is used to acknowledge receipt A Binding Acknowledgement option is used to acknowledge receipt
of a Binding Update, if an acknowledgement was requested of a Binding Update, if an acknowledgement was requested
in the Binding Update. Any packet that includes a Binding in the Binding Update. Any packet that includes a Binding
Acknowledgement option MUST also include either an AH [7] or Acknowledgement option MUST also include either an AH [8] or
ESP [8] header providing sender authentication, data integrity ESP [9] header providing sender authentication, data integrity
protection, and replay protection. The Binding Acknowledgement protection, and replay protection. The Binding Acknowledgement
option is described in detail in Section 5.2. option is described in detail in Section 5.2.
Binding Request Binding Request
A Binding Request option is used to request a mobile node A Binding Request option is used to request a mobile node to
to send a Binding Update to the requesting node, containing send to the requesting node a Binding Update containing the
the mobile node's current binding. This option is typically mobile node's current binding. This option is typically used
used by a correspondent node to refresh a cached binding for by a correspondent node to refresh a cached binding for a
a mobile node, when the cached binding is in active use but mobile node, when the cached binding is in active use but the
the binding's lifetime is close to expiration. No special binding's lifetime is close to expiration. No authentication
authentication is required for the Binding Request option. The is required for the Binding Request option. The Binding
Binding Request option is described in detail in Section 5.3. Request option is described in detail in Section 5.3.
Home Address Home Address
A Home Address option is used in a packet sent by a mobile A Home Address option is used in a packet sent by a mobile
node to inform the recipient of that packet of the mobile node to inform the recipient of that packet of the mobile
node's home address. For packets sent by a mobile node while node's home address. For packets sent by a mobile node while
away from home, the mobile node generally uses one of its away from home, the mobile node generally uses one of its
care-of addresses as the Source Address in the packet's IPv6 care-of addresses as the Source Address in the packet's IPv6
header. By including a Home Address option in the packet, the header. By including a Home Address option in the packet, the
correspondent node receiving the packet is able to substitute correspondent node receiving the packet is able to substitute
the mobile node's home address for this care-of address when the mobile node's home address for this care-of address when
processing the packet, thus making the use of the care-of processing the packet, thus making the use of the care-of
address transparent to the correspondent node. If the IP address transparent to the correspondent node. If the IP
header of a packet carrying a Home Address option is covered header of a packet carrying a Home Address option is covered
by authentication, then the Home Address option MUST also by authentication, then the Home Address option MUST also be
be covered by this authentication, but no other special covered by this authentication, but no other authentication is
authentication is required for the Home Address option. The required for the Home Address option. The Home Address option
Home Address option is described in detail in Section 5.4. is described in detail in Section 5.4.
Extensions to the format of these options MAY be included after the Extensions to the format of these options MAY be included after the
fixed portion of the option data specified in this document. The fixed portion of the option data specified in this document. The
presence of such extensions will be indicated by the Option Length presence of such extensions will be indicated by the Option Length
field within the option. When the Option Length is greater than the field within the option. When the Option Length is greater than the
length required for the option specified here, the remaining octets length required for the option specified here, the remaining octets
are interpreted as extensions. Currently, no extensions have been are interpreted as extensions. Currently, no extensions have been
defined. defined.
4.3. Conceptual Data Structures 4.3. Conceptual Data Structures
This document describes the Mobile IPv6 protocol in terms of the This document describes the Mobile IPv6 protocol in terms of the
following three conceptual data structures used in the maintenance of following three conceptual data structures:
cached bindings:
Binding Cache Binding Cache
A cache, maintained by each IPv6 node, of bindings for A cache, maintained by each IPv6 node, of bindings for other
other nodes. The Binding Cache MAY be implemented in any nodes. The Binding Cache MAY be implemented in any manner
manner consistent with the external behavior described consistent with the external behavior described in this
in this document, for example by being combined with the document, for example by being combined with the node's
node's Destination Cache as maintained through Neighbor Destination Cache as maintained by Neighbor Discovery [13].
Discovery [11]. When sending a packet, the Binding Cache When sending a packet, the Binding Cache is searched before the
MUST be searched before the Neighbor Discovery conceptual Neighbor Discovery conceptual Destination Cache [13] (i.e., any
Destination Cache [11]. Each Binding Cache entry conceptually Binding Cache entry for this destination SHOULD take precedence
contains the following fields: over any Destination Cache entry for the same destination).
Each Binding Cache entry conceptually contains the following
fields:
- The home address of the mobile node for which this is the - The home address of the mobile node for which this is the
Binding Cache entry. This field is used as the key for Binding Cache entry. This field is used as the key for
searching the Binding Cache for the destination address of searching the Binding Cache for the destination address of
a packet being routed. If the destination address of the a packet being sent. If the destination address of the
packet matches the home address in the Binding Cache entry, packet matches the home address in the Binding Cache entry,
this entry SHOULD be used in routing that packet. this entry SHOULD be used in routing that packet.
- The care-of address for the mobile node indicated by - The care-of address for the mobile node indicated by
the home address field in this Binding Cache entry. If the home address field in this Binding Cache entry. If
the destination address of a packet being routed by a the destination address of a packet being routed by a
node matches the home address in this entry, the packet node matches the home address in this entry, the packet
SHOULD be routed to this care-of address, as described in SHOULD be routed to this care-of address, as described in
Section 8.9, for packets originated by this node, or in Section 8.9, for packets originated by this node, or in
Section 9.5, if this node is the mobile node's home agent Section 9.6, if this node is the mobile node's home agent
and the packet was intercepted by it on the home link. and the packet was intercepted by it on the home link.
- A lifetime value, indicating the remaining lifetime - A lifetime value, indicating the remaining lifetime
for this Binding Cache entry. The lifetime value is for this Binding Cache entry. The lifetime value is
initialized from the Lifetime field in the Binding Update initialized from the Lifetime field in the Binding Update
that created or last modified this Binding Cache entry. that created or last modified this Binding Cache entry.
Once the lifetime on this entry expires, the entry MUST be Once the lifetime on this entry expires, the entry MUST be
deleted from the Binding Cache. deleted from the Binding Cache.
- A flag indicating whether or not this Binding Cache entry - A flag indicating whether or not this Binding Cache entry
is a "home registration" entry. is a "home registration" entry.
- The value of the Prefix Length field received in the - The value of the Prefix Length field received in the
Binding Update that created or last modified this Binding Binding Update that created or last modified this Binding
Cache entry. Cache entry. This field is only valid if the "home
registration" flag is set on this Binding Cache entry.
- The maximum value of the Sequence Number field received in
previous Binding Updates for this mobile node home address.
All comparisons between Sequence Number values MUST be - The maximum value of the Sequence Number field received
in previous Binding Updates for this mobile node home
address. The Sequence Number field is 16 bits long, and
all comparisons between Sequence Number values MUST be
performed modulo 2**16. performed modulo 2**16.
- Recent usage information for this Binding Cache entry, - Recent usage information for this Binding Cache entry, as
as needed for the cache replacement policy in use in the needed to implement the cache replacement policy in use in
Binding Cache and to assist in determining whether a the Binding Cache and to assist in determining whether a
Binding Request should be sent when the lifetime on this Binding Request should be sent when the lifetime on this
entry nears expiration. entry nears expiration.
- The time at which a Binding Request was last sent for this - The time at which a Binding Request was last sent for this
entry, as needed to implement the rate limiting restriction entry, as needed to implement the rate limiting restriction
for sending Binding Requests. for sending Binding Requests.
An entry in a node's Binding Cache for which the node is An entry in a node's Binding Cache for which the node is
serving as a home agent is marked as a "home registration" serving as a home agent is marked as a "home registration"
entry and SHOULD NOT be deleted by the home agent until the entry and SHOULD NOT be deleted by the home agent until the
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The Binding Update List includes all bindings sent by the The Binding Update List includes all bindings sent by the
mobile node: those to correspondent nodes, to the mobile mobile node: those to correspondent nodes, to the mobile
node's home agent, and to a previous default router of the node's home agent, and to a previous default router of the
mobile node. The Binding Update List MAY be implemented in any mobile node. The Binding Update List MAY be implemented in any
manner consistent with the external behavior described in this manner consistent with the external behavior described in this
document. Each Binding Update List entry conceptually contains document. Each Binding Update List entry conceptually contains
the following fields: the following fields:
- The IP address of the node to which a Binding Update was - The IP address of the node to which a Binding Update was
sent. This node might still have a Binding Cache entry sent. This node might still have a Binding Cache entry
derived from this Binding Update, if the Binding Update was created or updated from this Binding Update, if the Binding
successfully received by that node (e.g., not lost by the Update was successfully received by that node (e.g., not
network) and if that node has not deleted the entry before lost by the network) and if that node has not deleted the
its expiration (e.g., to reclaim space in its Binding Cache entry before its expiration (e.g., to reclaim space in its
for other entries). Binding Cache for other entries).
- The home address for which that Binding Update was sent. - The home address for which that Binding Update was sent.
This will be the mobile node's home address for most This will be one of the mobile node's home addresses for
Binding Updates (Sections 10.4 and 10.5), but will be most Binding Updates (Sections 10.5 and 10.7), but will
the mobile node's previous care-of address for Binding be the mobile node's previous care-of address for Binding
Updates sent to the mobile node's previous default router Updates sent to the mobile node's previous default router
(Section 10.6). (Section 10.8).
- The care-of address sent in that Binding Update. This - The care-of address sent in that Binding Update. This
value is necessary for determining if the mobile node has value is necessary for the mobile node to determine if it
sent a Binding Update giving its new care-of address to has sent a Binding Update giving its new care-of address to
this destination after changing its care-of address. this destination after changing its care-of address.
- The remaining lifetime of that binding. This lifetime is - The remaining lifetime of that binding. This lifetime is
initialized from the Lifetime value sent in the Binding initialized from the Lifetime value sent in the Binding
Update and is decremented until it reaches zero, at which Update and is decremented until it reaches zero, at which
time this entry MUST be deleted from the Binding Update time this entry MUST be deleted from the Binding Update
List. List.
- The maximum value of the Sequence Number field sent - The maximum value of the Sequence Number field sent in
in previous Binding Updates to this destination. All previous Binding Updates to this destination. The Sequence
comparisons between Sequence Number values MUST be Number field is 16 bits long, and all comparisons between
performed modulo 2**16. Sequence Number values MUST be performed modulo 2**16.
- The time at which a Binding Update was last sent to this
destination, as needed to implement the rate limiting
restriction for sending Binding Updates.
- The state of any retransmissions needed for this Binding - The state of any retransmissions needed for this Binding
Update, if the Acknowledge (A) bit was set in this Binding Update, if the Acknowledge (A) bit was set in this Binding
Update. This state includes the time remaining until the Update. This state includes the time remaining until the
next retransmission attempt for the Binding Update, and next retransmission attempt for the Binding Update, and the
the current state of the exponential back-off process for current state of the exponential back-off mechanism for
retransmissions. retransmissions.
- The time at which a Binding Update was last sent to this
destination, as needed to implement the rate limiting
restriction for sending Binding Updates.
- A flag that, when set, indicates that future Binding - A flag that, when set, indicates that future Binding
Updates should not be sent to this destination. The Updates should not be sent to this destination. The
mobile node sets this flag in the Binding Update List mobile node sets this flag in the Binding Update List
entry when it receives an ICMP Parameter Problem, Code 2, entry when it receives an ICMP Parameter Problem, Code 2,
error message in response to a Binding Update sent to that error message in response to a Binding Update sent to that
destination, as described in Section 10.9. destination, as described in Section 10.13.
Home Agents List Home Agents List
A list, maintained by each home agent, recording the IP address A list, maintained by each home agent, recording information
of each other home agent on a link on which this node is about each other home agent on a link on which this node
serving as a home agent; the home agent maintains a separate is serving as a home agent; each home agent maintains a
Home Agents List for each such link on which it is serving. separate Home Agents List for each such link on which it is
This list is used in the dynamic home agent address discovery serving. This list is used in the dynamic home agent address
mechanism. The information for the list is learned through discovery mechanism. The information for the list is learned
receipt of periodic unsolicited multicast Router Advertisements through receipt of the periodic unsolicited multicast Router
from each other home agent on the link, in which the Home Advertisements from each other home agent on the link, in which
Agent (H) bit is set, in a manner similar to the Default the Home Agent (H) bit is set, in a manner similar to the
Router List conceptual data structure maintained by each host Default Router List conceptual data structure maintained by
for Neighbor Discovery [11]. The Home Agents List MAY be each host for Neighbor Discovery [13]. The Home Agents List
implemented in any manner consistent with the external behavior MAY be implemented in any manner consistent with the external
described in this document. Each Home Agents List entry behavior described in this document. Each Home Agents List
conceptually contains the following fields: entry conceptually contains the following fields:
- The IP address of another router on the home link that this - The IP address of another router on the home link that this
node currently believes is operating as a home agent for node currently believes is operating as a home agent for
this link. A new entry is created or an existing entry is this link. A new entry is created or an existing entry is
updated in the Home Agents List in response to receipt of a updated in the Home Agents List in response to receipt of a
valid Router Advertisement in which the Home Agent (H) bit valid Router Advertisement in which the Home Agent (H) bit
is set. is set.
- The remaining lifetime of this Home Agents List entry. The - The remaining lifetime of this Home Agents List entry. If
lifetime is initialized from the Router Lifetime field in a Home Agent Information Option is present in a Router
the received Router Advertisement and is decremented until Advertisement received from a home agent, the lifetime of
it reaches zero, at which time this entry MUST be deleted the Home Agents List entry representing this home agent
from the Home Agents List. is initialized from the Home Agent Lifetime field in the
option; otherwise, the lifetime is initialized from the
Router Lifetime field in the received Router Advertisement.
The Home Agents List entry lifetime is decremented until it
reaches zero, at which time this entry MUST be deleted from
the Home Agents List.
- The preference for this home agent, for use in ordering the
Home Agents List returned in a Binding Acknowledgement;
higher values indicate a more preferable home agent. The
preference value is taken from the Home Agent Preference
field (a signed, twos-complement integer) in the received
Router Advertisement, if the Router Advertisement contains
a Home Agent Information Option, and is otherwise set to
the default value of 0.
4.4. Binding Management 4.4. Binding Management
When a mobile node configures a new care-of address and decides to When a mobile node configures a new care-of address and decides to
use this new address as its primary care-of address, the mobile use this new address as its primary care-of address, the mobile
node registers this new binding with its home agent by sending node registers this new binding with its home agent by sending
the home agent a Binding Update. The mobile node indicates the home agent a Binding Update. The mobile node indicates
that an acknowledgement is needed for this Binding Update and that an acknowledgement is needed for this Binding Update and
continues to periodically retransmit it until acknowledged. The continues to periodically retransmit it until acknowledged. The
home agent acknowledges the Binding Update by returning a Binding home agent acknowledges the Binding Update by returning a Binding
Acknowledgement to the mobile node. Acknowledgement to the mobile node.
When a mobile node receives a packet tunneled to it from its When a mobile node receives a packet tunneled to it from its
home agent, the mobile node assumes that the original sending home agent, the mobile node assumes that the original sending
correspondent node has no Binding Cache entry for the mobile node, correspondent node has no Binding Cache entry for the mobile node,
since the correspondent node would otherwise have sent the packet since the correspondent node would otherwise have sent the packet
directly to the mobile node using a Routing header. The mobile node directly to the mobile node using a Routing header. The mobile node
thus returns a Binding Update to the correspondent node, allowing thus returns a Binding Update to the correspondent node, allowing
it to cache the mobile node's binding for routing future packets. it to cache the mobile node's binding for routing future packets to
Although the mobile node may request an acknowledgement for this it. Although the mobile node may request an acknowledgement for
Binding Update, it need not, since subsequent packets from the this Binding Update, it need not, since subsequent packets from the
correspondent node will continue to be intercepted and tunneled by correspondent node will continue to be intercepted and tunneled by
the mobile node's home agent, effectively causing any needed Binding the mobile node's home agent, effectively causing any needed Binding
Update retransmission. Update retransmission.
A correspondent node with a Binding Cache entry for a mobile node A correspondent node with a Binding Cache entry for a mobile node
may refresh this binding, for example if the binding's lifetime may refresh this binding, for example if the binding's lifetime
is near expiration, by sending a Binding Request to the mobile is near expiration, by sending a Binding Request to the mobile
node. Normally, a correspondent node will only refresh a Binding node. Normally, a correspondent node will only refresh a Binding
Cache entry in this way if it is actively communicating with the Cache entry in this way if it is actively communicating with the
mobile node and has indications, such as an open TCP connection to mobile node and has indications, such as an open TCP connection to
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also eliminates congestion at the mobile node's home agent and home also eliminates congestion at the mobile node's home agent and home
link. In addition, the impact of any possible failure of the home link. In addition, the impact of any possible failure of the home
agent, the home link, or intervening networks leading to or from the agent, the home link, or intervening networks leading to or from the
home link is reduced, since these nodes and links are not involved in home link is reduced, since these nodes and links are not involved in
the delivery of most packets to the mobile node. the delivery of most packets to the mobile node.
5. New IPv6 Destination Options 5. New IPv6 Destination Options
5.1. Binding Update Option Format 5.1. Binding Update Option Format
The Binding Update destination option is used by a mobile node to The Binding Update destination option is used by a mobile node
notify other nodes of a new care-of address. to notify other nodes of a new care-of address for itself. As a
destination option, it MAY be included in any existing packet being
sent to this same destination or MAY be sent in a packet by itself;
a packet containing a Binding Update is sent in the same way as any
packet sent by a mobile node (Section 10.1).
The Binding Update option is encoded in type-length-value (TLV) The Binding Update option is encoded in type-length-value (TLV)
format as follows: format as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | | Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|C| Reserved| Prefix Length | Sequence Number | |A|H|C| Reserved| Prefix Length | Sequence Number |
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Option Length Option Length
8-bit unsigned integer. Length of the option, in octets, 8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields. For the excluding the Option Type and Option Length fields. For the
current definition of the Binding Update option, the minimum current definition of the Binding Update option, the minimum
value for this field is 8; the length is 24 if the Care-of value for this field is 8; the length is 24 if the Care-of
Address Present (C) bit is set. Address Present (C) bit is set.
Acknowledge (A) Acknowledge (A)
The Acknowledge (A) bit is set by the sending node to request a The Acknowledge (A) bit is set by the sending mobile node to
Binding Acknowledgement (Section 5.2) be returned upon receipt request a Binding Acknowledgement (Section 5.2) be returned
of the Binding Update option. upon receipt of the Binding Update.
Home Registration (H) Home Registration (H)
The Home Registration (H) bit is set by the sending mobile node The Home Registration (H) bit is set by the sending mobile node
to request the receiving node to act as this node's home agent. to request the receiving node to act as this node's home agent.
The destination of the packet carrying this option MUST be that
The Destination Address in the IP header of the packet carrying of a router sharing the same subnet prefix as the home address
this option MUST be that of a router sharing the same subnet of the mobile node in the binding (given by the Home Address
prefix as the home address of the mobile node in the binding field in the Home Address option in the packet).
(given by the Home Address field in the Home Address option in
the packet).
Care-of Address Present (C) Care-of Address Present (C)
The Care-of Address Present (C) bit indicates the presence of The Care-of Address Present (C) bit indicates the presence of
the Care-of Address field in the Binding Update. The care-of the Care-of Address field in the Binding Update. The care-of
address for this binding is either the address in the Care-of address for this binding is either the address in the Care-of
Address field in the Binding Update, if this bit is set, or the Address field in the Binding Update, if this bit is set, or the
Source Address in the packet's IPv6 header, if this bit is not Source Address in the packet's IPv6 header, if this bit is not
set. set.
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Prefix Length Prefix Length
The Prefix Length field is valid only for a "home registration" The Prefix Length field is valid only for a "home registration"
Binding Update. This field MUST be zero if the Home Binding Update. This field MUST be zero if the Home
Registration (H) bit is not set in the Binding Update. The Registration (H) bit is not set in the Binding Update. The
Prefix Length field is set by the sending mobile node to the Prefix Length field is set by the sending mobile node to the
(nonzero) length of its subnet prefix in its home address (nonzero) length of its subnet prefix in its home address
(given in the Home Address option in the packet) to request (given in the Home Address option in the packet) to request
its home agent to use the interface identifier in the mobile its home agent to use the interface identifier in the mobile
node's home address (the remaining low-order bits after the node's home address (the remaining low-order bits after the
indicated subnet prefix) to form all other appropriate home indicated subnet prefix) to form all other home addresses for
addresses for the mobile node. The home agent becomes the the mobile node on the home link. The home agent becomes the
home agent not only for the individual home address given in home agent not only for the individual home address given in
this binding, but also for all other home addresses for this this binding, but also for all other home addresses for this
mobile node formed from this interface identifier. That is, mobile node formed from this interface identifier. That is,
for each on-link prefix on the home link, the home agent uses for each on-link prefix on the home link, the home agent uses
the interface identifier to form other valid addresses for the the interface identifier to form other valid addresses for the
mobile node on the home link, and acts as a home agent also mobile node on the home link, and acts as a home agent also
for those addresses. In addition, the home agent forms the for those addresses. In addition, the home agent forms the
link-local address and site-local address corresponding to link-local address and site-local address corresponding to
this interface identifier, and defends each for purposes of this interface identifier, and defends each for purposes of
Duplicate Address Detection. Details of this operation are Duplicate Address Detection. Details of this operation are
described in Section 9.3. described in Section 9.3.
Sequence Number Sequence Number
Used by the receiving node to sequence Binding Updates and by Used by the receiving node to sequence Binding Updates and by
the sending node to match a returned Binding Acknowledgement the sending node to match a returned Binding Acknowledgement
with this Binding Update. Each Binding Update sent by a mobile with this Binding Update. Each Binding Update sent by a mobile
node MUST use a Sequence Number greater than the Sequence node MUST use a Sequence Number greater than the Sequence
Number value sent in the previous Binding Update (if any) to Number value sent in the previous Binding Update (if any) to
the same destination address (modulo 2**16). There is no the same destination address (modulo 2**16).
requirement, however, that the Sequence Number value strictly
increase by 1 with each new Binding Update sent or received.
Lifetime Lifetime
32-bit unsigned integer. The number of seconds remaining 32-bit unsigned integer. The number of seconds remaining
before the binding must be considered expired. A value of all before the binding must be considered expired. A value of all
one bits (0xffffffff) indicates infinity. A value of zero one bits (0xffffffff) indicates infinity. A value of zero
indicates that the Binding Cache entry for the mobile node indicates that the Binding Cache entry for the mobile node
should be deleted. should be deleted.
Care-of Address Care-of Address
This field in the Binding Update is optional and is only This field in the Binding Update is optional and is only
present when the Care-of Address Present (C) bit is set. If present when the Care-of Address Present (C) bit is set. If
present, it gives the care-of address of the mobile node for present, it gives the care-of address of the mobile node for
this binding. For most Binding Updates sent, it is expected this binding. For most Binding Updates sent, it is expected
that this field will not be present, and instead that the that this field will not be present, and instead that the
care-of address for the binding will be given by the Source care-of address for the binding will be given by the Source
Address field in the packet's IPv6 header. Address field in the packet's IPv6 header.
Any packet including a Binding Update option MUST also include a Home Any packet that includes a Binding Update option MUST also include
Address option. The home address of the mobile node in the binding a Home Address option. The home address of the mobile node in the
given in the Binding Update option is indicated by the Home Address binding given in the Binding Update option is indicated by the Home
field in the Home Address option in the packet. Address field in the Home Address option in the packet.
Any packet that includes a Binding Update option MUST also include Any packet that includes a Binding Update option MUST also include
either an AH [7] or ESP [8] header providing sender authentication, either an AH [8] or ESP [9] header providing sender authentication,
data integrity protection, and replay protection. data integrity protection, and replay protection.
If the care-of address in the binding (either the Care-of Address If the care-of address in the binding (either the Care-of Address
field in the Binding Update option or the Source Address field in field in the Binding Update option or the Source Address field in
the packet's IPv6 header) is equal to the home address of the mobile the packet's IPv6 header) is equal to the home address of the mobile
node, the Binding Update option indicates that any existing binding node, the Binding Update option indicates that any existing binding
for the mobile node should be deleted. Likewise, if the Lifetime for the mobile node MUST be deleted. Likewise, if the Lifetime
field in the Binding Update option is equal to 0, the Binding Update field in the Binding Update option is equal to 0, the Binding Update
option indicates that any existing binding for the mobile node should option indicates that any existing binding for the mobile node MUST
be deleted. In each of these cases, no Binding Cache entry for the be deleted. In each of these cases, a Binding Cache entry for the
mobile node should be created in response to receiving the Binding mobile node MUST NOT be created in response to receiving the Binding
Update. Update.
The last Sequence Number value sent to a destination is stored by the The last Sequence Number value sent to a destination in a Binding
mobile node in the Binding Update List entry for that destination; Update is stored by the mobile node in its Binding Update List entry
the last Sequence Number value received from a mobile node is stored for that destination; the last Sequence Number value received from
by a correspondent node in the Binding Cache entry for that mobile a mobile node in a Binding Update is stored by a correspondent node
node. Thus, the mobile node's and the correspondent node's knowledge in its Binding Cache entry for that mobile node. Thus, the mobile
of the last sequence number expire at the same time. If the sending node's and the correspondent node's knowledge of the last sequence
mobile node has no Binding Update List entry, the Sequence Number number expire at the same time. If the sending mobile node has no
may start at any value; if the receiving correspondent node has no Binding Update List entry, the Sequence Number may start at any
Binding Cache entry, it should accept a Binding Update with any value; if the receiving correspondent node has no Binding Cache entry
Sequence Number value. for the sending mobile node, it MUST accept any Sequence Number value
in a received Binding Update from this mobile node.
The three highest-order bits of the Option Type are encoded to The three highest-order bits of the Option Type are encoded to
indicate specific processing of the option [5]. For the Binding indicate specific processing of the option [5]. For the Binding
Update option, these three bits are set to 110, indicating that any Update option, these three bits are set to 110, indicating that any
IPv6 node processing this option that does not recognize the Option IPv6 node processing this option that does not recognize the Option
Type must discard the packet and, only if the packet's Destination Type must discard the packet and, only if the packet's Destination
Address was not a multicast address, return an ICMP Parameter Address was not a multicast address, return an ICMP Parameter
Problem, Code 2, message to the packet's Source Address; and that the Problem, Code 2, message to the packet's Source Address; and that the
data within the option cannot change en-route to the packet's final data within the option cannot change en-route to the packet's final
destination. destination.
skipping to change at page 20, line 9 skipping to change at page 23, line 9
the fixed portion of the Binding Update option specified above. the fixed portion of the Binding Update option specified above.
The presence of such extensions will be indicated by the Option The presence of such extensions will be indicated by the Option
Length field. When the Option Length is greater than the length Length field. When the Option Length is greater than the length
defined above, the remaining octets are interpreted as extensions. defined above, the remaining octets are interpreted as extensions.
Currently, no extensions have been defined. Currently, no extensions have been defined.
5.2. Binding Acknowledgement Option Format 5.2. Binding Acknowledgement Option Format
The Binding Acknowledgement destination option is used to acknowledge The Binding Acknowledgement destination option is used to acknowledge
receipt of a Binding Update option (Section 5.1). When a node receipt of a Binding Update option (Section 5.1). When a node
receives a packet containing a Binding Update option, with this node receives a packet containing a Binding Update option, with this
being the destination node of the packet (only the destination node node being the destination of the packet (only the destination node
processes the option since it is a destination option), this node processes the option since it is a destination option), this node
MUST return a Binding Acknowledgement to the source of the packet, if MUST return a Binding Acknowledgement to the source of the packet,
the Acknowledge (A) bit is set in the Binding Update. if the Acknowledge (A) bit is set in the Binding Update. As a
destination option, this node MAY included it in any existing packet
being sent to the mobile node or MAY send it in a packet by itself; a
packet containing a Binding Acknowledgement is sent in the same way
as any packet to a mobile node (Section 8.9).
The Binding Acknowledgement option is encoded in type-length-value The Binding Acknowledgement option is encoded in type-length-value
(TLV) format as follows: (TLV) format as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Option Type | | Option Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Length | Status | Sequence Number | | Option Length | Status | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime | | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Refresh | | Refresh |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
. . . .
. Other Home Agents . . Home Agents List .
. . . .
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type Option Type
2 ??? 2 ???
Option Length Option Length
8-bit unsigned integer. Length of the option, in octets, 8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields. This field excluding the Option Type and Option Length fields. This field
MUST be set to 11 + 16 * (the number of IP addresses included MUST be set to 11, except when the Status field is equal to 135
in the Other Home Agents field). The number of addresses (dynamic home agent address discovery response), in which case
included in the Other Home Agents field MUST be zero (Option this field MUST be set to 11 + 16 * N, where N is the number of
Length then MUST be set to 11), unless the Status field is set IP addresses included in the Home Agents List field; the Home
to 135 (dynamic home agent address discovery response). Agents List field MUST NOT be included in the option if the
Status field is not set to 135.
Status Status
8-bit unsigned integer indicating the disposition of the 8-bit unsigned integer indicating the disposition of the
Binding Update. Values of the Status field less than 128 Binding Update. Values of the Status field less than 128
indicate that the Binding Update was accepted by the receiving indicate that the Binding Update was accepted by the receiving
node. The following such Status values are currently defined: node. The following such Status values are currently defined:
0 Binding Update accepted 0 Binding Update accepted
skipping to change at page 21, line 27 skipping to change at page 24, line 29
128 Reason unspecified 128 Reason unspecified
129 Poorly formed Binding Update 129 Poorly formed Binding Update
130 Administratively prohibited 130 Administratively prohibited
131 Insufficient resources 131 Insufficient resources
132 Home registration not supported 132 Home registration not supported
133 Not home subnet 133 Not home subnet
134 Sequence Number field value too small 134 Sequence Number field value too small
135 Dynamic home agent address discovery response 135 Dynamic home agent address discovery response
136 Incorrect interface identifier length 136 Incorrect interface identifier length
137 Not home agent for this mobile node
Up-to-date values of the Status field are to be specified in Up-to-date values of the Status field are to be specified in
the most recent "Assigned Numbers" [17]. the most recent "Assigned Numbers" [21].
Sequence Number Sequence Number
The Sequence Number in the Binding Acknowledgement is copied The Sequence Number in the Binding Acknowledgement is copied
from the Sequence Number field in the Binding Update option, from the Sequence Number field in the Binding Update being
for use by the mobile node in matching this Acknowledgement acknowledged, for use by the mobile node in matching this
with an outstanding Binding Update. Acknowledgement with an outstanding Binding Update.
Lifetime Lifetime
The granted lifetime for which this node will attempt to retain The granted lifetime for which this node will attempt to retain
the entry for this mobile node in its Binding Cache. If the the entry for this mobile node in its Binding Cache. If the
node sending the Binding Acknowledgement is serving as the node sending the Binding Acknowledgement is serving as the
mobile node's home agent, the Lifetime period also indicates mobile node's home agent, the Lifetime period also indicates
the period for which this node will continue this service; if the period for which this node will continue this service; if
the mobile node requires home agent service from this node the mobile node requires home agent service from this node
beyond this period, the mobile node MUST send a new Binding beyond this period, the mobile node MUST send a new Binding
Update to it before the expiration of this period, in order Update to it before the expiration of this period (even if
to extend the lifetime. The value of this field is undefined it is not changing its primary care-of address), in order to
extend the lifetime. The value of this field is undefined
if the Status field indicates that the Binding Update was if the Status field indicates that the Binding Update was
rejected. rejected.
Refresh Refresh
The recommended period at which the mobile node SHOULD send The recommended interval at which the mobile node SHOULD send
a new Binding Update to this node in order to "refresh" the a new Binding Update to this node in order to "refresh" the
mobile node's binding in this node's Binding Cache. This mobile node's binding in this node's Binding Cache. This
refreshing of the binding is useful in case the node fails and refreshing of the binding is useful in case the node fails and
loses its cache state. The Refresh period is determined by loses its cache state. The Refresh period is determined by
the node sending the Binding Acknowledgement (the node caching the node sending the Binding Acknowledgement (the node caching
the binding). If this node is serving as the mobile node's the binding). If this node is serving as the mobile node's
home agent, the Refresh value may be set, for example, based on home agent, the Refresh value may be set, for example, based on
whether the node stores the mobile node's binding in volatile whether the node stores its Binding Cache in volatile storage
storage or in nonvolatile storage. If the node sending the or in nonvolatile storage. If the node sending the Binding
Binding Acknowledgement is not serving as the mobile node's Acknowledgement is not serving as the mobile node's home agent,
home agent, the Refresh period SHOULD be set equal to the the Refresh period SHOULD be set equal to the Lifetime period
Lifetime period in the Binding Acknowledgement; even if this in the Binding Acknowledgement; even if this node loses this
node loses this cache entry due to a failure of the node, cache entry due to a failure of the node, packets from it can
packets from it can still reach the mobile node through the still reach the mobile node through the mobile node's home
mobile node's home agent, causing a new Binding Update to this agent, causing a new Binding Update to this node to allow it
node to allow it to recreate this cache entry. The value of to recreate this cache entry. The value of this field is
this field is undefined if the Status field indicates that the undefined if the Status field indicates that the Binding Update
Binding Update was rejected. was rejected.
Other Home Agents Home Agents List
A list of other home agents on the home link for the mobile A list of home agents on the home link for the mobile node to
node to which this Binding Acknowledgement is sent. This field which this Binding Acknowledgement is sent. This field MUST
MUST NOT be present (zero addresses listed) unless the Binding NOT be present (zero addresses listed) unless the Binding
Acknowledgement is sent in response to an anycast Binding Acknowledgement is sent in response to an anycast Binding
Update sent by this mobile node attempting dynamic home agent Update sent by this mobile node attempting dynamic home agent
address discovery. In this case, the Status field MUST be address discovery. In this case, the Status field MUST be
set to 135 (dynamic home agent address discovery response). set to 135 (dynamic home agent address discovery response).
The list of home agents in the Other Home Agents field MUST The construction of the Home Agents List field in a Binding
NOT include this home agent's own unicast IP address, which Acknowledgement is defined in Section 9.2.
is returned instead to the mobile node in the Source Address
field in the IPv6 header of the packet in which this Binding
Acknowledgement is sent.
Any packet that includes a Binding Acknowledgement option MUST Any packet that includes a Binding Acknowledgement option MUST
also include either an AH [7] or ESP [8] header providing sender also include either an AH [8] or ESP [9] header providing sender
authentication, data integrity protection, and replay protection. authentication, data integrity protection, and replay protection.
If the node returning the Binding Acknowledgement accepted the If the node returning the Binding Acknowledgement accepted the
Binding Update for which the Acknowledgement is being returned (the Binding Update for which the Acknowledgement is being returned (the
value of the Status field in the Acknowledgement is less than 128), value of the Status field in the Acknowledgement is less than 128),
this node will have an entry for the mobile node in its Binding Cache this node will have an entry for the mobile node in its Binding Cache
and MUST use this entry (which includes the care-of address received and MUST use this entry (which includes the care-of address received
in the Binding Update) in sending the packet containing the Binding in the Binding Update) in sending the packet containing the Binding
Acknowledgement to the mobile node. The details of sending this Acknowledgement to the mobile node. The details of sending this
packet to the mobile node are the same as for sending any packet to a packet to the mobile node are the same as for sending any packet to a
skipping to change at page 24, line 8 skipping to change at page 27, line 8
indicate specific processing of the option [5]. For the Binding indicate specific processing of the option [5]. For the Binding
Acknowledgement option, these three bits are set to 000, indicating Acknowledgement option, these three bits are set to 000, indicating
that any IPv6 node processing this option that does not recognize the that any IPv6 node processing this option that does not recognize the
Option Type must skip over this option and continue processing the Option Type must skip over this option and continue processing the
header, and that the data within the option cannot change en-route to header, and that the data within the option cannot change en-route to
the packet's final destination. the packet's final destination.
5.3. Binding Request Option Format 5.3. Binding Request Option Format
The Binding Request destination option is used to request a mobile The Binding Request destination option is used to request a mobile
node's binding from the mobile node. When a mobile node receives node's binding from the mobile node. As a destination option, it
a packet containing a Binding Request option, it SHOULD return a MAY be included in any existing packet being sent to the mobile
Binding Update (Section 5.1) to the source of the Binding Request. node or MAY be sent in a packet by itself; a packet containing a
Binding Request option is sent in the same way as any packet to a
mobile node (Section 8.9). When a mobile node receives a packet
containing a Binding Request option, it SHOULD return a Binding
Update (Section 5.1) to the source of the Binding Request.
The Binding Request option is encoded in type-length-value (TLV) The Binding Request option is encoded in type-length-value (TLV)
format as follows: format as follows:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | | Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 25, line 8 skipping to change at page 28, line 8
Extensions to the Binding Request option format may be included after Extensions to the Binding Request option format may be included after
the fixed portion of the Binding Request option specified above. the fixed portion of the Binding Request option specified above.
The presence of such extensions will be indicated by the Option The presence of such extensions will be indicated by the Option
Length field. When the Option Length is greater than 0 octets, Length field. When the Option Length is greater than 0 octets,
the remaining octets are interpreted as extensions. Currently, no the remaining octets are interpreted as extensions. Currently, no
extensions have been defined. extensions have been defined.
5.4. Home Address Option Format 5.4. Home Address Option Format
The Home Address destination option is used in a packet sent by a The Home Address destination option is used in a packet sent by a
mobile node to inform the recipient of that packet of the mobile mobile node while away from home, to inform the recipient of that
node's home address. For packets sent by a mobile node while packet of the mobile node's home address. For packets sent by a
away from home, the mobile node generally uses one of its care-of mobile node while away from home, the mobile node generally uses
addresses as the Source Address in the packet's IPv6 header. By one of its care-of addresses as the Source Address in the packet's
including a Home Address option in the packet, the correspondent IPv6 header. By including a Home Address option in the packet, the
node receiving the packet is able to substitute the mobile node's correspondent node receiving the packet is able to substitute the
home address for this care-of address when processing the packet, mobile node's home address for this care-of address when processing
thus making the use of the care-of address transparent to the the packet, thus making the use of the care-of address transparent to
correspondent node. the correspondent node.
The Home Address option is encoded in type-length-value (TLV) format The Home Address option is encoded in type-length-value (TLV) format
as follows: as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | | Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
skipping to change at page 25, line 50 skipping to change at page 28, line 50
8-bit unsigned integer. Length of the option, in octets, 8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields. For the excluding the Option Type and Option Length fields. For the
current definition of the Home Address option, this field MUST current definition of the Home Address option, this field MUST
be set to 16. be set to 16.
Home Address Home Address
The home address of the mobile node sending the packet. The home address of the mobile node sending the packet.
The inclusion of a Home Address option in a packet affects only The inclusion of a Home Address option in a packet affects the
the correspondent node's receipt of this single packet; no state receiving node's processing of only this single packet; no state is
is created or modified in the correspondent node as a result of created or modified in the receiving node as a result of receiving a
receiving a Home Address option in a packet. In particular, the Home Address option in a packet. In particular, the presence of a
receipt of a packet containing a Home Address option MUST NOT alter Home Address option in a received packet MUST NOT alter the contents
the contents of the receiver's Binding Cache due to the presence of of the receiver's Binding Cache and MUST NOT cause any changes in the
the Home Address option, and the mapping between the home address routing of subsequent packets sent by this receiving node.
and care-of address indicated by the Home Address option MUST NOT be
used as a basis for routing subsequent packets sent by this receiving
node.
No special authentication of the Home Address option is required, No authentication of the Home Address option is required, except that
except that if the IPv6 header of a packet is covered by if the IPv6 header of a packet is covered by authentication, then
authentication, then that authentication MUST also cover the Home that authentication MUST also cover the Home Address option; this
Address option; this coverage is achieved automatically by the coverage is achieved automatically by the definition of the Option
definition of the Option Type code for the Home Address option, Type code for the Home Address option, since it indicates that the
since it indicates that the option is included in the authentication data within the option cannot change en-route to the packet's final
destination, and thus the option is included in the authentication
computation. If the packet carries no IP authentication, then the computation. If the packet carries no IP authentication, then the
contents of the Home Address option, as well as the Source Address contents of the Home Address option, as well as the Source Address
field or any other field in the IPv6 header, may have been forged or field or any other field in the IPv6 header, may have been forged or
altered during transit. Upon receipt of a packet containing a Home altered during transit.
Address option, the receiving node replaces the Source Address in
the IPv6 header with the Home Address in the Home Address option. Upon receipt of a packet containing a Home Address option, the
By requiring that any authentication of the IPv6 header also cover receiving node replaces the Source Address in the IPv6 header with
the Home Address option, the security of the Source Address field in the Home Address in the Home Address option. By requiring that any
the IPv6 header is not compromised by the presence of a Home Address authentication of the IPv6 header also cover the Home Address option,
option. Security issues related to the Home Address option are the security of the Source Address field in the IPv6 header is not
discussed further in Section 13. compromised by the presence of a Home Address option. Security
issues related to the Home Address option are discussed further in
Section 13.
The three highest-order bits of the Option Type are encoded to The three highest-order bits of the Option Type are encoded to
indicate specific processing of the option [5]. For the Home Address indicate specific processing of the option [5]. For the Home Address
option, these three bits are set to 110, indicating that any IPv6 option, these three bits are set to 110, indicating that any IPv6
node processing this option that does not recognize the Option Type node processing this option that does not recognize the Option Type
must discard the packet and, only if the packet's Destination Address must discard the packet and, only if the packet's Destination Address
was not a multicast address, return an ICMP Parameter Problem, was not a multicast address, return an ICMP Parameter Problem,
Code 2, message to the packet's Source Address; and that the data Code 2, message to the packet's Source Address; and that the data
within the option cannot change en-route to the packet's final within the option cannot change en-route to the packet's final
destination. destination.
Extensions to the Home Address option format may be included after Extensions to the Home Address option format may be included after
the fixed portion of the Home Address option specified above. the fixed portion of the Home Address option specified above.
The presence of such extensions will be indicated by the Option The presence of such extensions will be indicated by the Option
Length field. When the Option Length is greater than 8 octets, Length field. When the Option Length is greater than 8 octets,
the remaining octets are interpreted as extensions. Currently, no the remaining octets are interpreted as extensions. Currently, no
extensions have been defined. extensions have been defined.
6. Modifications to IPv6 Neighbor Discovery 6. Modifications to IPv6 Neighbor Discovery
6.1. Router Advertisement Message Format 6.1. Modified Router Advertisement Message Format
Mobile IPv6 requires the addition of a single flag bit to the format Mobile IPv6 modifies the format of the Router Advertisement
of a Router Advertisement message [11], for use in the dynamic home message [13] by the addition of a single flag bit for use in the
agent address discovery mechanism (Sections 9.2 and 10.4). The dynamic home agent address discovery mechanism (Sections 9.2
Router Advertisement message format is thus modified as follows: and 10.6). The format of the Router Advertisement message is
as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum | | Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cur Hop Limit |M|O|H| Reserved| Router Lifetime | | Cur Hop Limit |M|O|H| Reserved| Router Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time | | Reachable Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer | | Retrans Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ... | Options ...
+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+-+-+-+-+-+-+-+-+-
This format represents the following changes over that specified for This format represents the following changes over that originally
Neighbor Discovery [11]: specified for Neighbor Discovery [13]:
Home Agent (H) Home Agent (H)
The Home Agent (H) bit is set in a Router Advertisement to The Home Agent (H) bit is set in a Router Advertisement to
indicate that the router sending this Router Advertisement is indicate that the router sending this Router Advertisement is
also functioning as a Mobile IP home agent. also functioning as a Mobile IP home agent.
Reserved Reserved
Reduced from a 6-bit field to a 5-bit field to account for the Reduced from a 6-bit field to a 5-bit field to account for the
addition of the Home Agent (H) bit. addition of the Home Agent (H) bit.
6.2. Advertisement Interval Option Format 6.2. Modified Prefix Information Option Format
The Advertisement Interval option is used in Router Advertisement Mobile IPv6 requires knowledge of a router's global address for two
messages to advertise the interval at which this router sends reasons:
unsolicited multicast Router Advertisements. Routers operating
as Mobile IP home agents MAY include this option in their Router
Advertisements. A mobile node receiving a Router Advertisement
containing this option SHOULD utilize the specified Advertisement
Interval for that home agent in its movement detection algorithm, as
described in Section 10.2.
This option MUST be silently ignored for other Neighbor Discovery - To allow a home agent (a router) to learn the address of all
messages. other home agents on the link for which it is proving home agent
service, for use in building its Home Agents List as part of the
dynamic home agent address discovery mechanism (Sections 9.2
and 10.6).
- To allow a mobile node to send a Binding Update to its previous
default router, after moving to a new subnet and acquiring a new
care-of address (Section 10.8).
However, Neighbor Discovery [13] only advertises a router's
link-local address, by requiring this address to be used as the IP
Source Address of each Router Advertisement.
Mobile IPv6 extends Neighbor Discovery to allow a router to easily
and efficiently advertise its global address, by the addition of a
single flag bit in the format of a Prefix Information option for
use in Router Advertisement messages. The format of the Prefix
Information option is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Prefix Length |L|A|R|Reserved1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Prefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This format represents the following changes over that originally
specified for Neighbor Discovery [13]:
Router Address (R)
1-bit router address flag. When set, indicates that the
Prefix field, in addition to advertising the indicated prefix,
contains a complete IP address assigned to the sending router.
This router IP address has the same scope and conforms to the
same lifetime values as the advertised prefix. This use of
the Prefix field is compatible with its use in advertising
the prefix itself, since prefix advertisement uses only the
leading number Prefix bits specified by the Prefix Length
field. Interpretation of this flag bit is thus independent
of the processing required for the On-Link (L) and Autonomous
Address-Configuration (A) flag bits.
Reserved1
Reduced from a 6-bit field to a 5-bit field to account for the
addition of the Router Address (R) bit.
In a solicited Router Advertisement, a router MUST include at least
one Prefix Information option with the Router Address (R) bit set.
Neighbor Discovery specifies that, if including all options in a
Router Advertisement causes the size of the Advertisement to exceed
the link MTU, multiple Advertisements can be sent, each containing
a subset of the options [13]. In this case, at least one of these
multiple Advertisements begin sent instead of a single larger
solicited Advertisement, MUST include a Prefix Information option
with the Router Address (R) bit set.
All routers SHOULD include at least one Prefix Information option
with the Router Address (R) bit set, in each unsolicited multicast
Router Advertisement that they send. If multiple Advertisements
are being sent instead of a single larger unsolicited multicast
Advertisement, at least one of these multiple Advertisements SHOULD
include a Prefix Information option with the Router Address (R) bit
set.
6.3. New Advertisement Interval Option Format
Mobile IPv6 defines a new Advertisement Interval option, used in
Router Advertisement messages to advertise the interval at which the
sending router sends unsolicited multicast Router Advertisements.
The format of the Advertisement Interval option is as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved | | Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertisement Interval | | Advertisement Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type Type
6 ??? 6 ???
Length Length
1 8-bit unsigned integer. The length of the option (including
the type and length fields) in units of 8 octets. The value of
this field MUST be 1.
Reserved Reserved
This field is unused. It MUST be initialized to zero by the This field is unused. It MUST be initialized to zero by the
sender and MUST be ignored by the receiver. sender and MUST be ignored by the receiver.
Advertisement Interval Advertisement Interval
32-bit unsigned integer. The maximum time, in milliseconds, 32-bit unsigned integer. The maximum time, in milliseconds,
between successive unsolicited router Router Advertisement between successive unsolicited router Router Advertisement
messages sent by this router on this network interface. Using messages sent by this router on this network interface. Using
the conceptual router configuration variables defined by the conceptual router configuration variables defined by
Neighbor Discovery [11], this field MUST be equal to the value Neighbor Discovery [13], this field MUST be equal to the value
MaxRtrAdvInterval, expressed in milliseconds. MaxRtrAdvInterval, expressed in milliseconds.
6.3. Changes to MinRtrAdvInterval Limits Routers MAY include this option in their Router Advertisements. A
mobile node receiving a Router Advertisement containing this option
SHOULD utilize the specified Advertisement Interval for that router
in its movement detection algorithm, as described in Section 10.3.
The Neighbor Discovery protocol specification [11] limits routers to This option MUST be silently ignored for other Neighbor Discovery
messages.
6.4. New Home Agent Information Option Format
Mobile IPv6 defines a new Home Agent Information option, used in
Router Advertisement messages sent by a home agent to advertise
information specific to this router's functionality as a home agent.
The format of the Home Agent Information option is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Agent Preference | Home Agent Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
7 ???
Length
8-bit unsigned integer. The length of the option (including
the type and length fields) in units of 8 octets. The value of
this field MUST be 1.
Reserved
This field is unused. It MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
Home Agent Preference
16-bit signed, twos-complement integer. The preference
for the home agent sending this Router Advertisement, for
use in ordering the Home Agents List returned in a Binding
Acknowledgement; higher values mean more preferable. If this
option is not included in a Router Advertisement in which the
Home Agent (H) bit is set, the preference value for this home
agent SHOULD be considered to be 0. Values greater than 0
indicate a home agent more preferable than this default value,
and values less than 0 indicate a less preferable home agent.
Home Agent Lifetime
16-bit unsigned integer. The lifetime associated with the home
agent in units of seconds. The maximum value corresponds to
18.2 hours. A value of 0 MUST NOT be used. The Home Agent
Lifetime applies only to this router's usefulness as a home
agent; it does not apply to information contained in other
message fields or options. If this option is not included in
a Router Advertisement in which the Home Agent (H) bit is set,
the lifetime for this home agent SHOULD be considered to be the
same as the Router Lifetime specified in the main body of the
Router Advertisement message.
Home agents MAY include this option in their Router Advertisements.
This option MUST NOT be included in a Router Advertisement in which
the Home Agent (H) bit (Section 6.1) is not set.
This option MUST be silently ignored for other Neighbor Discovery
messages.
If both the Home Agent Preference and Home Agent Lifetime are set
to their default values specified above, this option SHOULD NOT be
included in the Router Advertisement messages sent by this home
agent.
6.5. Changes to Sending Router Advertisements
The Neighbor Discovery protocol specification [13] limits routers to
a minimum interval of 3 seconds between sending unsolicited multicast a minimum interval of 3 seconds between sending unsolicited multicast
Router Advertisement messages from any given network interface Router Advertisement messages from any given network interface
(MinRtrAdvInterval), stating that: (limited by MinRtrAdvInterval and MaxRtrAdvInterval), stating that:
"Routers generate Router Advertisements frequently enough "Routers generate Router Advertisements frequently enough
that hosts will learn of their presence within a few that hosts will learn of their presence within a few
minutes, but not frequently enough to rely on an absence minutes, but not frequently enough to rely on an absence
of advertisements to detect router failure; a separate of advertisements to detect router failure; a separate
Neighbor Unreachability Detection algorithm provides failure Neighbor Unreachability Detection algorithm provides failure
detection." detection."
This limitation, however, is not suitable to providing timely This limitation, however, is not suitable to providing timely
movement detection for mobile nodes. Mobile nodes detect their movement detection for mobile nodes. Mobile nodes detect their
own movement by learning the presence of new routers as the mobile own movement by learning the presence of new routers as the mobile
node moves into wireless transmission range of them (or physically node moves into wireless transmission range of them (or physically
connects to a new wired network), and by learning that previous connects to a new wired network), and by learning that previous
routers are no longer reachable. Mobile nodes MUST be able to routers are no longer reachable. Mobile nodes MUST be able to
quickly detect when they move to a link served by a new router, so quickly detect when they move to a link served by a new router, so
that they can acquire a new care-of address and send Binding Updates that they can acquire a new care-of address and send Binding Updates
to register this care-of address with their home agent and to notify to register this care-of address with their home agent and to notify
correspondent nodes as needed. correspondent nodes as needed.
Thus, routers serving as Mobile IP home agents MAY send unsolicited Thus, to provide good support for mobile nodes, Mobile IPv6 relaxes
multicast Router Advertisements more frequently than this limit. In this limit such that routers MAY send unsolicited multicast Router
particular, on network interfaces where the home agent is expecting Advertisements more frequently. In particular, on network interfaces
to provide service to visiting mobile nodes (e.g., wireless network where the router is expecting to provide service to visiting mobile
interfaces), the home agent SHOULD be configured with a smaller nodes (e.g., wireless network interfaces), or on which it is serving
MinRtrAdvInterval value to allow sending of unsolicited multicast as a home agent to one or more mobile nodes (who may return home and
Router Advertisements more often. A recommended maximum rate is need to hear its Advertisements), the home agent SHOULD be configured
once per second, although specific knowledge of the type of network with a smaller MinRtrAdvInterval value and MaxRtrAdvInterval value,
to allow sending of unsolicited multicast Router Advertisements more
often. Recommended values for these limits are:
- MinRtrAdvInterval 0.5 seconds
- MaxRtrAdvInterval 1.5 seconds
Use of these modified limits MUST be configurable, and specific
knowledge of the type of network interface in use SHOULD be taken
into account in configuring these limits for each network interface.
When sending unsolicited multicast Router Advertisements more
frequently than the standard limit on unsolicited multicast
Advertisement frequency, the sending router need not include all
options in each of these Advertisements, but it SHOULD include at
least one Prefix Information option with the Router Address (R) bit
set (Section 6.2) in each.
6.6. Changes to Sending Router Solicitations
In addition to the limit on routers sending unsolicited multicast
Router Advertisement messages (Section 6.5), Neighbor Discovery
defines limits on nodes sending Router Solicitation messages, such
that a node SHOULD send no more than 3 Router Solicitations, and that
these 3 transmissions SHOULD be spaced at least 4 seconds apart.
However, these limits prevent a mobile node from finding a new
default router (and thus a new care-of address) quickly as it moves
about.
Mobile IPv6 relaxes this limit such that, while a mobile node is away
from home, it MAY send Router Solicitations more frequently. The
following limits for sending Router Solicitations are recommended for
mobile nodes while away from home:
- A mobile node that is not configured with any current care-of
address (e.g., the mobile node has moved since its previous
care-of address was configured), MAY send more than the defined
Neighbor Discovery limit of MAX_RTR_SOLICITATIONS Router
Solicitations.
- The rate at which a mobile node sends Router Solicitations MUST
be limited, although a mobile node MAY send Router Solicitations
more frequently than the defined Neighbor Discovery limit of
RTR_SOLICITATION_INTERVAL seconds. The minimum interval MUST
be configurable, and specific knowledge of the type of network
interface in use SHOULD be taken into account in configuring this interface in use SHOULD be taken into account in configuring this
limit for each network interface. limit for each network interface. A recommended minimum interval
is 1 second.
- After sending at most MAX_RTR_SOLICITATIONS Router Solicitations,
a mobile node MUST reduce the rate at which it sends subsequent
Router Solicitations. Subsequent Router Solicitations SHOULD
be sent using a binary exponential backoff mechanism, doubling
the interval between consecutive Router Solicitations, up to a
maximum interval. The maximum interval MUST be configurable and
SHOULD be chosen appropriately based on the characteristics of
the type of network interface in use.
- While still searching for a new default router and care-of
address, a mobile node MUST NOT increase the rate at which it
sends Router Solicitations unless it has received a positive
indication (such as from lower network layers) that it has moved
to a new link. After successfully acquiring a new care-of
address, the mobile node SHOULD also increase the rate at which
it will send Router Solicitations when it next begins searching
for a new default router and care-of address.
- A mobile node that is currently configured with a care-of
address SHOULD NOT send Router Solicitations, until its movement
detection algorithm (Section 10.3) determines that it has moved
and that its current care-of address might no longer be valid.
7. Requirements for IPv6 Nodes 7. Requirements for IPv6 Nodes
Mobile IPv6 places some special requirements on the functions Mobile IPv6 places some special requirements on the functions
provided by different IPv6 nodes. This section summarizes those provided by different types of IPv6 nodes. This section summarizes
requirements, identifying the functionality each requirement is those requirements, identifying the functionality each requirement
intended to support. Further details on this functionality is is intended to support. Further details on this functionality is
provided in the following sections. provided in the following sections.
7.1. Requirements for All IPv6 Hosts and Routers 7.1. Requirements for All IPv6 Hosts and Routers
Since any IPv6 node may at any time be a correspondent node of a Since any IPv6 node may at any time be a correspondent node of a
mobile node, either sending a packet to a mobile node or receiving a mobile node, either sending a packet to a mobile node or receiving a
packet from a mobile node, the following requirements pertain to ALL packet from a mobile node, the following requirements apply to ALL
IPv6 nodes (whether host or router, whether mobile or stationary): IPv6 nodes (whether host or router, whether mobile or stationary):
- Every IPv6 node MUST be able to process a Home Address option - Every IPv6 node MUST be able to process a Home Address option
received in a packet. received in any IPv6 packet.
- Every IPv6 node SHOULD be able to process a Binding Update option - Every IPv6 node SHOULD be able to process a Binding Update option
received in a packet, and to return a Binding Acknowledgement received in a packet, and to return a Binding Acknowledgement
option if requested. option if the Acknowledge (A) bit is set in the received Binding
Update.
- Every IPv6 node SHOULD be able to maintain a Binding Cache of the - Every IPv6 node SHOULD be able to maintain a Binding Cache of the
bindings received in accepted Binding Updates. bindings received in accepted Binding Updates.
7.2. Requirements for IPv6 Home Agents 7.2. Requirements for All IPv6 Routers
In order for a mobile node to operate correctly while away from The following requirements apply to all IPv6 routers, even those not
home, at least one IPv6 router in the mobile node's home link must serving as a home agent for Mobile IPv6:
function as a home agent for the mobile node. The following special
requirements pertain to all IPv6 routers capable of serving as a home - Every IPv6 router SHOULD be able to send an Advertisement
Interval option in its Router Advertisements, to aid movement
detection by mobile nodes. The use of this option in Router
Advertisements MUST be configurable.
- Every IPv6 router SHOULD be able to support sending unsolicited
multicast Router Advertisements at the faster rate described in
Section 6.5. The use of this faster rate MUST be configurable.
7.3. Requirements for IPv6 Home Agents
In order for a mobile node to operate correctly while away from home,
at least one IPv6 router on the mobile node's home link must function
as a home agent for the mobile node. The following additional
requirements apply to all IPv6 routers capable of serving as a home
agent: agent:
- Every home agent MUST be able to maintain an entry in its Binding - Every home agent MUST be able to maintain an entry in its Binding
Cache for each mobile node for which it is serving as the home Cache for each mobile node for which it is serving as the home
agent. Each such Binding Cache entry records the mobile node's agent. Each such Binding Cache entry records the mobile node's
binding with its primary care-of address and is marked as a "home binding with its primary care-of address and is marked as a "home
registration". registration".
- Every home agent MUST be able to intercept packets (using proxy - Every home agent MUST be able to intercept packets (using proxy
Neighbor Discovery) on the local subnet addressed to a mobile Neighbor Discovery) addressed to a mobile node for which it is
node for which it is currently serving as the home agent while currently serving as the home agent, on that mobile node's home
that mobile node is away from home. link, while the mobile node is away from home.
- Every home agent MUST be able to encapsulate such intercepted - Every home agent MUST be able to encapsulate such intercepted
packets in order to tunnel them to the primary care-of address packets in order to tunnel them to the primary care-of address
for the mobile node indicated in its binding. for the mobile node indicated in its binding in the home agent's
Binding Cache.
- Every home agent MUST be able to return a Binding Acknowledgement - Every home agent MUST be able to return a Binding Acknowledgement
in response to a Binding Update received with the Acknowledge (A) option in response to a Binding Update option received with the
bit set. Acknowledge (A) bit set.
- Every home agent MUST be able to accept packets addressed to the - Every home agent MUST be able to accept packets addressed to the
Home-Agents anycast address for the subnet on which it is serving Home-Agents anycast address for the subnet on which it is serving
as a home agent, and MUST be able to participate in dynamic home as a home agent, and MUST be able to participate in dynamic home
agent address discovery (Section 9.2). agent address discovery (Section 9.2).
7.3. Requirements for IPv6 Mobile Nodes 7.4. Requirements for IPv6 Mobile Nodes
Finally, the following requirements pertain all IPv6 nodes capable of Finally, the following requirements apply to all IPv6 nodes capable
functioning as mobile nodes: of functioning as mobile nodes:
- Every IPv6 mobile node MUST be able to perform IPv6 - Every IPv6 mobile node MUST be able to perform IPv6
decapsulation [4]. decapsulation [4].
- Every IPv6 mobile node MUST support sending Binding Updates, as - Every IPv6 mobile node MUST support sending Binding Update
specified in Sections 10.4, 10.5, and 10.6; and MUST be able to options, as specified in Sections 10.5, 10.7, and 10.8; and MUST
receive and process Binding Acknowledgements, as specified in be able to receive and process Binding Acknowledgement options,
Section 10.10. as specified in Section 10.11.
- Every IPv6 mobile node MUST support use of the dynamic home agent
address discovery mechanism, as described in Section 10.6.
- Every IPv6 mobile node MUST maintain a Binding Update List in - Every IPv6 mobile node MUST maintain a Binding Update List in
which it records the IP address of each other node to which it which it records the IP address of each other node to which it
has sent a Binding Update, for which the Lifetime sent in that has sent a Binding Update, for which the Lifetime sent in that
binding has not yet expired. binding has not yet expired.
- Every IPv6 mobile node MUST support receiving a Binding Request - Every IPv6 mobile node MUST support receiving a Binding Request
by responding with a Binding Update. option, by responding with a Binding Update option.
- Every IPv6 mobile node MUST support sending packets containing a - Every IPv6 mobile node MUST support sending packets containing a
Home Address option; this option MUST be included in all packets Home Address option; this option MUST be included in all packets
sent while away from home, if the packet would otherwise have sent while away from home, if the packet would otherwise have
been sent with the mobile node's home address as the IP Source been sent with the mobile node's home address as the IP Source
Address. Address.
8. Correspondent Node Operation 8. Correspondent Node Operation
A correspondent node is any node communicating with a mobile node. A correspondent node is any node communicating with a mobile node.
skipping to change at page 32, line 19 skipping to change at page 42, line 19
possibly also be functioning as a home agent for Mobile IPv6. The possibly also be functioning as a home agent for Mobile IPv6. The
procedures in this section thus apply to all IPv6 nodes. procedures in this section thus apply to all IPv6 nodes.
8.1. Receiving Packets from a Mobile Node 8.1. Receiving Packets from a Mobile Node
Packets sent by a mobile node while away from home generally include Packets sent by a mobile node while away from home generally include
a Home Address option. When any node receives a packet containing a Home Address option. When any node receives a packet containing
a Home Address option, it MUST process the option in a manner a Home Address option, it MUST process the option in a manner
consistent with copying the Home Address field from the Home Address consistent with copying the Home Address field from the Home Address
option into the IPv6 header, replacing the original value of the option into the IPv6 header, replacing the original value of the
Source Address field there. Further processing of the packet (e.g., Source Address field there.
at the transport layer) thus need not know that the original Source
Address was a care-of address, or that the Home Address option was Further processing of such a packet (e.g., at the transport layer)
used in the packet. Since the sending mobile node uses its home thus need not know that the original Source Address was a care-of
address at the transport layer when sending such a packet, the use of address, or that the Home Address option was used in the packet.
the care-of address and Home Address option is thus transparent to Since the sending mobile node uses its home address at the transport
both the mobile node and the correspondent node above the level of layer when sending such a packet, the use of the care-of address
the Home Address option generation and processing. and Home Address option is transparent to both the mobile node and
the correspondent node above the level of the Home Address option
generation and processing.
8.2. Receiving Binding Updates 8.2. Receiving Binding Updates
Upon receiving a Binding Update option in some packet, the receiving Upon receiving a Binding Update option in some packet, the receiving
node MUST validate the Binding Update according to the following node MUST validate the Binding Update according to the following
tests: tests:
- The packet contains a valid AH [8] or ESP [9] header that
provides sender authentication, integrity protection, and replay
protection.
- The packet MUST contain a valid Home Address option. The home - The packet MUST contain a valid Home Address option. The home
address for the binding is specified by the Home Address field of address for the binding is specified by the Home Address field of
the Home Address option. the Home Address option.
- The Option Length field in the Binding Update option is greater - The Option Length field in the Binding Update option is greater
than or equal to the length specified in Section 5.1. than or equal to the length specified in Section 5.1.
- The packet contains a valid AH [7] or ESP [8] header that
provides sender authentication, integrity protection, and replay
protection.
- The Sequence Number field in the Binding Update option is greater - The Sequence Number field in the Binding Update option is greater
than the Sequence Number received in the previous Binding Update than the Sequence Number received in the previous Binding Update
for this home address, if any. The Sequence Number comparison is for this home address, if any. The Sequence Number comparison is
performed modulo 2**16. performed modulo 2**16.
Any Binding Update not satisfying all of these tests MUST be Any Binding Update not satisfying all of these tests MUST be
silently ignored, and the packet carrying the Binding Update MUST be silently ignored, and the packet carrying the Binding Update MUST be
discarded. discarded.
If the Binding Update is valid according to the tests above, then the If the Binding Update is valid according to the tests above, then the
Binding Update is processed further as follows: Binding Update is processed further as follows:
- If the Destination Address in the packet's IPv6 header is the - If the Destination Address in the packet's IPv6 header is the
Home-Agents anycast address for a local subnet and this address Home-Agents anycast address for a local prefix and this address
is assigned to one of this node's network interfaces, then the is assigned to one of this node's network interfaces, then the
mobile node sending this Binding Update is attempting dynamic mobile node sending this Binding Update is attempting dynamic
home agent address discovery. Processing for this type of home agent address discovery. Processing for this type of
received Binding Update is described in Section 9.2. (If the received Binding Update is described in Section 9.2. (If the
Destination Address is not assigned to one of this node's network Destination Address is not assigned to one of this node's network
interfaces, then the packet would have been forwarded as a normal interfaces, then the packet would have been forwarded as a normal
packet and the Binding Update, as a destination option, would not packet and the Binding Update, as a destination option, would not
be processed in any way by this node.) be processed in any way by this node.)
- If the Lifetime specified in the Binding Update is nonzero and - If the Lifetime specified in the Binding Update is nonzero and
the specified Care-of Address is not equal to the home address the specified Care-of Address is not equal to the home address
for the binding (as given in the Home Address option in the for the binding (as given in the Home Address option in the
packet), then this is a request to cache a binding for the mobile packet), then this is a request to cache a binding for the
node. Processing for this type of received Binding Update is mobile node. If the Home Registration (H) bit is set in the
described in Section 8.3. Binding Update, the Binding Update is processed according to the
procedure specified in Section 9.3; otherwise, it is processed
according to the procedure specified in Section 8.3.
- If the Lifetime specified in the Binding Update is zero or the - If the Lifetime specified in the Binding Update is zero or the
specified Care-of Address matches the home address for the specified Care-of Address matches the home address for the
binding, then this is a request to delete the mobile node's binding, then this is a request to delete the mobile node's
cached binding. Processing for this type of received Binding cached binding. If the Home Registration (H) bit is set in the
Update is described in Section 8.4. Binding Update, the Binding Update is processed according to the
procedure specified in Section 9.4; otherwise, it is processed
according to the procedure specified in Section 8.4.
8.3. Requests to Cache a Binding 8.3. Requests to Cache a Binding
If a node receives a valid Binding Update requesting it to cache a When a node receives a Binding Update, it MUST validate it and
binding for a mobile node, as specified in Section 8.2, then the node determine the type of Binding Update according to the steps described
MUST examine the Home Registration (H) bit in the Binding Update in Section 8.2. This section describes the processing of a valid
to determine how to further process the Binding Update. If the Binding Update that requests a node to cache a mobile node's binding,
Home Registration (H) bit is set, the Binding Update is processed for which the Home Registration (H) bit is not set in the Binding
according to the procedure specified in Section 9.3. Update.
If the Home Registration (H) bit is not set, then the receiving In this case, the receiving node SHOULD create a new entry in its
node SHOULD create a new entry in its Binding Cache for this mobile Binding Cache for this mobile node (or update its existing Binding
node (or update its existing Binding Cache entry for this mobile Cache entry for this mobile node, if such an entry already exists).
node, if such an entry already exists). The home address of the The home address of the mobile node is taken from the Home Address
mobile node is taken from the Home Address field in the packet's Home field in the packet's Home Address option. The new Binding Cache
Address option. The new Binding Cache entry records the association entry records the association between this home address and the
between this home address and the care-of address for the binding, as care-of address for the binding, as specified in either the Care-of
specified in either the Care-of Address field of the Binding Update Address field of the Binding Update or in the Source Address field
or in the Source Address field in the packet's IPv6 header. Any in the packet's IPv6 header. Any Binding Cache entry created or
Binding Cache entry created or updated in response to processing this updated in response to processing this Binding Update MUST be deleted
Binding Update MUST be deleted after the expiration of the Lifetime after the expiration of the Lifetime period specified in the Binding
period specified in the Binding Update. Update.
8.4. Requests to Delete a Binding 8.4. Requests to Delete a Binding
If a node receives a valid Binding Update requesting it to delete a When a node receives a Binding Update, it MUST validate it and
cached binding for a mobile node, as specified in Section 8.2, then determine the type of Binding Update according to the steps described
the node MUST examine the Home Registration (H) bit in the Binding in Section 8.2. This section describes the processing of a valid
Update to determine how to further process the Binding Update. If Binding Update that requests a node to delete a mobile node's binding
the Home Registration (H) bit is set, the Binding Update is processed from its Binding Cache, for which the Home Registration (H) bit is
according to the procedure specified in Section 9.4. not set in the Binding Update.
If the Home Registration (H) bit is not set, then the receiving node In this case, the receiving node MUST delete any existing entry in
MUST delete any existing entry in its Binding Cache for this mobile its Binding Cache for this mobile node. The home address of the
node. The home address of the mobile node is taken from the Home mobile node is taken from the Home Address field in the packet's Home
Address field in the packet's Home Address option. Address option.
8.5. Sending Binding Acknowledgements 8.5. Sending Binding Acknowledgements
When any node receives a packet containing a Binding Update option When any node receives a packet containing a Binding Update option
in which the Acknowledge (A) bit is set, it SHOULD return a Binding in which the Acknowledge (A) bit is set, it SHOULD return a Binding
Acknowledgement option acknowledging receipt of the Binding Update. Acknowledgement option acknowledging receipt of the Binding Update.
If the node accepts the Binding Update and creates or updates an If the node accepts the Binding Update and creates or updates an
entry in its Binding Cache for this binding, the Status field in entry in its Binding Cache for this binding, the Status field in
the Binding Acknowledgement MUST be set to a value less than 128; the Binding Acknowledgement MUST be set to a value less than 128;
if the node rejects the Binding Update and does not create or if the node rejects the Binding Update and does not create or
update an entry for this binding, the Status field in the Binding update an entry for this binding, the Status field in the Binding
Acknowledgement MUST be set to a value greater than or equal to 128. Acknowledgement MUST be set to a value greater than or equal to 128.
Specific values for the Status field are described in Section 5.2 and Specific values for the Status field are described in Section 5.2 and
in the most recent "Assigned Numbers" [17]. in the most recent "Assigned Numbers" [21].
As described in Section 5.2, the packet in which the Binding As described in Section 5.2, the packet in which the Binding
Acknowledgement is returned MUST include either an AH [7] or ESP [8] Acknowledgement is returned MUST include either an AH [8] or ESP [9]
header providing sender authentication, data integrity protection, header providing sender authentication, data integrity protection,
and replay protection; and the packet MUST be sent using a Routing and replay protection; and the packet MUST be sent using a Routing
header in the same way as any other packet sent to a mobile node header in the same way as any other packet sent to a mobile node
using a care-of address (even if the binding was rejected), as using a care-of address (even if the binding was rejected), as
described in Section 8.9. The packet is routed first to the care-of described in Section 8.9. The packet is routed first to the care-of
address contained in the Binding Update being acknowledged, and address contained in the Binding Update being acknowledged, and
then to the mobile node's home address. This use of the Routing then to the mobile node's home address. This use of the Routing
header ensures that the Binding Acknowledgement will be routed to the header ensures that the Binding Acknowledgement will be routed to the
current location of the node sending the Binding Update, whether the current location of the node sending the Binding Update, whether the
Binding Update was accepted or rejected. Binding Update was accepted or rejected.
8.6. Sending Binding Requests 8.6. Sending Binding Requests
Entries in a node's Binding Cache MUST be deleted when their lifetime Entries in a node's Binding Cache MUST be deleted when their lifetime
expires. If such an entry is still in active use in sending packets expires. If such an entry is still in active use in sending packets
to a mobile node, the next packet sent to the mobile node will be to a mobile node, the next packet sent to the mobile node will be
routed normally, to the mobile node's home link, where it will be routed normally to the mobile node's home link, where it will be
intercepted and tunneled to the mobile node. The mobile node will intercepted and tunneled to the mobile node. The mobile node will
then return a Binding Update to the sender, allowing it to create then return a Binding Update to the sender, allowing it to create
a new Binding Cache entry for sending future packets to the mobile a new Binding Cache entry for sending future packets to the mobile
node. Communication with the mobile node continues uninterrupted, node. Communication with the mobile node continues uninterrupted,
but the forwarding of this packet through the mobile node's home but the forwarding of this packet through the mobile node's home
agent creates additional overhead and latency in delivering packets agent creates additional overhead and latency in delivering packets
to the mobile node. to the mobile node.
If the sender knows that the Binding Cache entry is still in active If the sender knows that the Binding Cache entry is still in active
use, it MAY send a Binding Request to the mobile node in an attempt use, it MAY send a Binding Request option to the mobile node in
to avoid this overhead and latency due to deleting and recreating an attempt to avoid this overhead and latency due to deleting and
the Binding Cache entry. Since a Binding Request is a destination recreating the Binding Cache entry. Since a Binding Request is a
option, it may, for example, be included in any packet already being destination option, it may, for example, be included in any packet
sent to the mobile node, such as a packet that is part of ongoing TCP already being sent to the mobile node, such as a packet that is part
communication with the mobile node. When the mobile node receives a of ongoing TCP communication with the mobile node. When the mobile
packet from some sender containing a Binding Request, it returns a node receives a packet from some sender containing a Binding Request
Binding Update to that sender, giving its current binding and a new option, it returns a Binding Update option to that sender, giving its
lifetime. current binding and a new lifetime.
8.7. Cache Replacement Policy 8.7. Cache Replacement Policy
Any entry in a node's Binding Cache MUST be deleted after the Any entry in a node's Binding Cache MUST be deleted after the
expiration of the Lifetime specified in the Binding Update from which expiration of the Lifetime specified in the Binding Update from
the entry was created or was last updated. Conceptually, a node which the entry was created or last updated. Conceptually, a node
maintains a separate timer for each entry in its Binding Cache. When maintains a separate timer for each entry in its Binding Cache. When
creating or updating a Binding Cache entry in response to a received creating or updating a Binding Cache entry in response to a received
and accepted Binding Update, the node sets the timer for this entry and accepted Binding Update, the node sets the timer for this entry
to the specified Lifetime period. When a Binding Cache entry's timer to the specified Lifetime period. When a Binding Cache entry's timer
expires, the node deletes the entry. expires, the node deletes the entry.
Each node's Binding Cache will, by necessity, have a finite size. Each node's Binding Cache will, by necessity, have a finite size.
A node MAY use any reasonable local policy for managing the space A node MAY use any reasonable local policy for managing the space
within its Binding Cache, except that any entry marked as a "home within its Binding Cache, except that any entry marked as a "home
registration" (Section 9.3) MUST NOT be deleted from the cache until registration" (Section 9.3) MUST NOT be deleted from the cache until
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space will be rediscovered and a new cache entry created, if the space will be rediscovered and a new cache entry created, if the
binding is still in active use by the node for sending packets. If binding is still in active use by the node for sending packets. If
the node sends a packet to a destination for which it has dropped the the node sends a packet to a destination for which it has dropped the
entry from its Binding Cache, the packet will be routed normally, entry from its Binding Cache, the packet will be routed normally,
leading to the mobile node's home link. There, the packet will be leading to the mobile node's home link. There, the packet will be
intercepted by the mobile node's home agent and tunneled to the intercepted by the mobile node's home agent and tunneled to the
mobile node's current primary care-of address. As when a Binding mobile node's current primary care-of address. As when a Binding
Cache entry is initially created, this indirect routing to the mobile Cache entry is initially created, this indirect routing to the mobile
node through its home agent will result in the mobile node sending node through its home agent will result in the mobile node sending
a Binding Update to this sending node when it receives the tunneled a Binding Update to this sending node when it receives the tunneled
packet, allowing it to add an entry again for this destination to its packet, allowing it to add an entry again for this destination mobile
Binding Cache. node to its Binding Cache.
8.8. Receiving ICMP Error Messages 8.8. Receiving ICMP Error Messages
When a correspondent node sends a packet to a mobile node, if the When a correspondent node sends a packet to a mobile node, if the
correspondent node has a Binding Cache entry for the destination correspondent node has a Binding Cache entry for the destination
address of the packet, then the correspondent node uses a Routing address of the packet, then the correspondent node uses a Routing
header to deliver the packet to the mobile node through the care-of header to deliver the packet to the mobile node through the care-of
address in the binding recorded in the Binding Cache entry. Any ICMP address in the binding recorded in the Binding Cache entry. Any ICMP
error message caused by the packet on its way to the mobile node will error message caused by the packet on its way to the mobile node will
be returned normally to the correspondent node. be returned normally to the correspondent node.
On the other hand, if the correspondent node has no Binding Cache On the other hand, if the correspondent node has no Binding Cache
entry for the mobile node, the packet will be routed to the mobile entry for the mobile node, the packet will be routed to the mobile
node's home link, where it will be intercepted by the mobile node's node's home link. There, it will be intercepted by the mobile node's
home agent, encapsulated, and tunneled to the mobile node's primary home agent, encapsulated, and tunneled to the mobile node's primary
care-of address. Any ICMP error message caused by the packet on care-of address. Any ICMP error message caused by the packet on
its way to the mobile node while in the tunnel, will be returned to its way to the mobile node while in the tunnel, will be returned to
the mobile node's home agent (the source of the tunnel). By the the mobile node's home agent (the source of the tunnel). By the
definition of IPv6 encapsulation [4], this encapsulating node MUST definition of IPv6 encapsulation [4], this encapsulating node MUST
relay certain ICMP error messages back to the original sender of the relay certain ICMP error messages back to the original sender of the
packet, which in this case is the correspondent node. packet, which in this case is the correspondent node.
Likewise, if a packet for a mobile node arrives at the mobile node's Likewise, if a packet for a mobile node arrives at the mobile node's
previous default router (e.g., the mobile node moved after the packet previous default router (e.g., the mobile node moved after the packet
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be delivered to the mobile node (the mobile node has associated the be delivered to the mobile node (the mobile node has associated the
care-of address with its network interface). Normal processing of care-of address with its network interface). Normal processing of
the Routing header by the mobile node will then proceed as follows: the Routing header by the mobile node will then proceed as follows:
- The mobile node swaps the Destination Address in the packet's - The mobile node swaps the Destination Address in the packet's
IPv6 header and the Address specified in the Routing header. IPv6 header and the Address specified in the Routing header.
This results in the packet's IP Destination Address being set to This results in the packet's IP Destination Address being set to
the mobile node's home address. the mobile node's home address.
- The mobile node then resubmits the packet to its IPv6 module for - The mobile node then resubmits the packet to its IPv6 module for
further processing. Since the mobile node recognizes its own further processing, "looping back" the packet inside the mobile
home address as one if its current IP addresses, the packet is node. Since the mobile node recognizes its own home address as
processed further within the mobile node, in the same way then as one of its current IP addresses, the packet is processed further
if the mobile node was at home. within the mobile node, in the same way then as if the mobile
node was at home.
If, instead, the sending node has no Binding Cache entry for the If, instead, the sending node has no Binding Cache entry for the
destination address to which the packet is being sent, the sending destination address to which the packet is being sent, the sending
node simply sends the packet normally, with no Routing header. If node simply sends the packet normally, with no Routing header. If
the destination node is not a mobile node (or is a mobile node that the destination node is not a mobile node (or is a mobile node that
is currently at home), the packet will be delivered directly to this is currently at home), the packet will be delivered directly to this
node and processed normally by it. If, however, the destination node node and processed normally by it. If, however, the destination node
is a mobile node that is currently away from home, the packet will is a mobile node that is currently away from home, the packet will
be intercepted by the mobile node's home agent and tunneled (using be intercepted by the mobile node's home agent and tunneled (using
IPv6 encapsulation [4]) to the mobile node's current primary care-of IPv6 encapsulation [4]) to the mobile node's current primary care-of
address, as described in Section 9.5. The mobile node will then send address, as described in Section 9.6. The mobile node will then send
a Binding Update to the sending node, as described in Section 10.5, a Binding Update to the sending node, as described in Section 10.7,
allowing the sending node to create a Binding Cache entry for its use allowing the sending node to create a Binding Cache entry for its use
in sending subsequent packets to this mobile node. in sending subsequent packets to this mobile node.
9. Home Agent Operation 9. Home Agent Operation
9.1. Receiving Router Advertisement Messages 9.1. Receiving Router Advertisement Messages
For each link on which a router provides service as a home agent, For each link on which a router provides service as a home agent, the
the router maintains a Home Agents List recording the IP address of router maintains a Home Agents List recording information about all
all other home agents that link. This list is used in the dynamic other home agents on that link. This list is used in the dynamic
home agent address discovery mechanism, described in Section 9.2. home agent address discovery mechanism, described in Section 9.2.
The information for the list is learned through receipt of periodic The information for the list is learned through receipt of the
unsolicited multicast Router Advertisements from each other home periodic unsolicited multicast Router Advertisements from each other
agent on the link, in which the Home Agent (H) bit is set, in a home agent on the link, in which the Home Agent (H) bit is set, in a
manner similar to the Default Router List conceptual data structure manner similar to the Default Router List conceptual data structure
maintained by each host for Neighbor Discovery [11]. maintained by each host for Neighbor Discovery [13].
On receipt of a valid Router Advertisement, as defined in the On receipt of a valid Router Advertisement, as defined in the
processing algorithm specified for Neighbor Discovery [11], the home processing algorithm specified for Neighbor Discovery [13], the home
agent extracts the Source Address of the packet and performs the agent performs the following steps, in addition to any steps already
following steps, in addition to any steps already required of it by required of it by Neighbor Discovery:
Neighbor Discovery:
- If the address is not already present in the home agent's Home - If the Home Agent (H) bit in the Router Advertisement is not set,
Agents List, and the advertisement's Router Lifetime is non-zero, skip all of the following steps. There are no special processing
create a new entry in the list, and initialize its lifetime from steps required by Mobile IP for this Router Advertisement, since
the advertisement's Router Lifetime field. the Advertisement was not sent by a home agent.
- If the address is already present in the home agent's Home Agents - Otherwise, extract the Source Address from the IP header of the
List as a result of a previously-received advertisement, reset Router Advertisement. This is the link-local IP address on
its lifetime to the Router Lifetime value in the newly-received this link of the home agent sending this Advertisement [13].
advertisement. Determine the global address of the router based on the
Prefix Information option received from it in which the Router
Address (R) bit is set (Section 6.2).
- If the address is already present in the home agent's Home Agents - Determine from the Router Advertisement the preference for this
List and the received Router Lifetime value is zero, immediately home agent. If the Router Advertisement contains a Home Agent
delete this entry in the Home Agents List Information Option, then the preference is taken from the Home
Agent Preference field in the option; otherwise, the default
preference of 0 SHOULD be used.
- Determine from the Router Advertisement the lifetime for
this home agent. If the Router Advertisement contains a Home
Agent Information Option, then the lifetime is taken from
the Home Agent Lifetime field in the option; otherwise, the
lifetime specified by the Router Lifetime field in the Router
Advertisement SHOULD be used.
- If the global address of the home agent sending this
Advertisement, as determined above, is not already present in the
Home Agents List maintained by the receiving home agent, and the
lifetime for the sending home agent, also as determined above,
is non-zero, create a new entry in the list, and initialize its
lifetime and preference to the values determined above.
- If the global address of the home agent sending this
Advertisement is already present in the receiving home agent's
Home Agents List, reset its lifetime and preference to the values
determined above.
- If the address is already present in this home agent's Home
Agents List and the received home agent lifetime value is zero,
immediately delete this entry in the Home Agents List.
A home agent SHOULD maintain an entry in its Home Agents List for A home agent SHOULD maintain an entry in its Home Agents List for
each such valid home agent address until that entry's lifetime each such valid home agent address until that entry's lifetime
expires, after which time the entry MUST be deleted. expires, after which time the entry MUST be deleted.
9.2. Dynamic Home Agent Address Discovery 9.2. Dynamic Home Agent Address Discovery
If a received Binding Update indicates that the mobile node sending When a node receives a Binding Update, it MUST validate it and
it is attempting dynamic home agent address discovery, as described determine the type of Binding Update according to the steps described
in Section 8.2, then the receiving node MUST process the Binding in Section 8.2. This section describes the processing of a valid
Update as specified in this section. Binding Update that indicates that the mobile node sending it is
attempting dynamic home agent address discovery.
A mobile node attempts dynamic home agent address discovery by As described in Section 10.6, a mobile node attempts dynamic home
sending its "home registration" Binding Update to the Home-Agents agent address discovery by sending its "home registration" Binding
anycast address for its home IP subnet prefix (the packet MUST also Update to the Home-Agents anycast address for its home IP subnet
include a Home Address option, as described in Section 10.4). A home prefix (the packet MUST also include a Home Address option). A home
agent receiving such a Binding Update that is serving this subnet agent receiving such a Binding Update that is serving this subnet
(the home agent is configured with this anycast address on one of its (the home agent is configured with this anycast address on one of its
network interfaces) MUST reject the Binding Update and SHOULD return network interfaces) MUST reject the Binding Update and SHOULD return
a Binding Acknowledgement indicating this rejection, with the Source a Binding Acknowledgement indicating this rejection, with the Source
Address of the packet carrying the Binding Acknowledgement set to Address of the packet carrying the Binding Acknowledgement set to one
one of the unicast addresses of the home agent. The Status field in of the global unicast addresses of the home agent. The Status field
the Binding Acknowledgement MUST be set to 135 (dynamic home agent in the Binding Acknowledgement MUST be set to 135 (dynamic home agent
address discovery response). address discovery response).
In this Binding Acknowledgement rejecting the dynamic home agent In this Binding Acknowledgement rejecting the dynamic home agent
address discovery Binding Update, this home agent SHOULD include the address discovery Binding Update, this home agent SHOULD set the Home
IP address of all other home agents currently listed in its Home Agents List as follows:
Agents List. To include this list in the Binding Acknowledgement,
the Option Length field MUST be set to 11 + 16 * (the number - The Home Agents List in this Binding Acknowledgement SHOULD
of IP addresses included in the Other Home Agents field in the contain the IP address of all home agents currently listed in
Binding Acknowledgement). The mobile node, upon receiving this this home agent's own Home Agents List (Section 4.3). However,
Binding Acknowledgement, MAY then resend its Binding Update to if this home agent's own IP address would be placed in the list
the unicast home agent address given as the IP Source Address of (as described below) as the first entry in the list, then this
the packet carrying the Binding Acknowledgement or to any of the home agent SHOULD NOT include its own address in the list in
unicast IP addresses listed in the Other Home Agents field in the Binding Acknowledgement. Not placing this home agent's own
the Acknowledgement. For example, the mobile node may re-attempt IP address in the list will cause the receiving mobile node
its home registration with each of these home agents in turn, by to consider this home agent as the most preferred home agent;
sending each a Binding Update and waiting for the matching Binding otherwise, this home agent will be considered to be preferred in
Acknowledgement, until its registration is accepted by one of these its order given by its place in the list returned.
home agents.
- The IP addresses in the Home Agents List should be placed in
the Home Agents List in the Binding Acknowledgement in order
of decreasing preference value, based either on the respective
advertised preference from a Home Agent Information option or on
the default preference of 0 if no preference is advertised (or on
the configured home agent preference for this home agent itself).
The home agent with the highest preference SHOULD be listed
first, and the home agent with the lowest preference SHOULD be
listed last.
- Among home agents with equal preference, their IP addresses in
the Home Agents List SHOULD be listed in an order randomized with
respect to other home agents with equal preference, each time
a Binding Acknowledgement with a non-empty Home Agents List is
returned by this home agent.
- The Option Length field in this Binding Acknowledgement
MUST be set to 11 + 16 * N, where N is the number of IP
addresses included in the Home Agents List field in the Binding
Acknowledgement.
The mobile node, upon receiving this Binding Acknowledgement, MAY
then resend its Binding Update to the home agent address given as the
IP Source Address of the packet carrying the Binding Acknowledgement
or to any of the unicast IP addresses listed in the Home Agents List
field in the Acknowledgement. For example, the mobile node may
re-attempt its home registration with each of these home agents in
turn, by sending each a Binding Update and waiting for the matching
Binding Acknowledgement, until its registration is accepted by one
of these home agents. In trying each of the returned home agent
addresses, the mobile node SHOULD try each in the order listed in the
Home Agents List in the Binding Acknowledgement. If the home agent
identified by the Source Address field in the IP header of the packet
carrying the Binding Acknowledgement is not listed in the Home Agents
List, it SHOULD be tried before the first address given in the list;
otherwise, it SHOULD be tried in the in its listed order.
9.3. Primary Care-of Address Registration 9.3. Primary Care-of Address Registration
General processing of a received Binding Update that requests a When a node receives a Binding Update, it MUST validate it and
binding to be cached, is described in Section 8.3. However, if determine the type of Binding Update according to the steps described
the Home Registration (H) bit is set in the Binding Update, then in Section 8.2. This section describes the processing of a valid
after following the step outlined for all Binding Update options in Binding Update that requests the receiving node to serve as its home
Section 8.2, the receiving node MUST process the Binding Update as agent, registering its primary care-of address.
specified in this section rather than following the general procedure
for requests to cache a binding specified in Section 8.3.
To begin processing the Binding Update, the home agent MUST perform To begin processing the Binding Update, the home agent MUST perform
the following sequence of tests: the following sequence of tests:
- If the node is not a router that implements home agent - If the node is not a router that implements home agent
functionality, then the node MUST reject the Binding Update and functionality, then the node MUST reject the Binding Update and
SHOULD return a Binding Acknowledgement to the mobile node, in SHOULD return a Binding Acknowledgement to the mobile node, in
which the Status field is set to 132 (home registration not which the Status field is set to 132 (home registration not
supported). supported).
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- Else, if the home agent chooses to reject the Binding Update for - Else, if the home agent chooses to reject the Binding Update for
any other reason (e.g., insufficient resources to serve another any other reason (e.g., insufficient resources to serve another
mobile node as a home agent), then the home agent SHOULD return a mobile node as a home agent), then the home agent SHOULD return a
Binding Acknowledgement to the mobile node, in which the Status Binding Acknowledgement to the mobile node, in which the Status
field is set to an appropriate value to indicate the reason for field is set to an appropriate value to indicate the reason for
the rejection. the rejection.
If the home agent does not reject the Binding Update as described If the home agent does not reject the Binding Update as described
above, then it becomes the home agent for the mobile node. The new above, then it becomes the home agent for the mobile node. The new
home agent (the receiving node) MUST then create a new entry or home agent (the receiving node) MUST then create a new entry in its
update the existing entry in its Binding Cache for this mobile node's Binding Cache for this mobile node (or update its existing Binding
home address (given in the Home Address option in the packet), as Cache entry for this mobile node, if such an entry already exists)
described in Section 8.3. In addition, the home agent MUST mark The home address of the mobile node is taken from the Home Address
this Binding Cache entry as a "home registration" to indicate that field in the packet's Home Address option. The care-of address for
the node is serving as a home agent for this binding. Binding this Binding Cache entry is taken from the Care-of Address field of
Cache entries marked as a "home registration" MUST be excluded from the Binding Update (if the Care-of Address Present (C) bit is set in
the normal cache replacement policy used for the Binding Cache the Binding Update) or from the Source Address field in the packet's
(Section 8.7) and MUST NOT be removed from the Binding Cache until IPv6 header (otherwise).
the expiration of the Lifetime period.
If the home agent was not already serving as a home agent for this The home agent MUST mark this Binding Cache entry as a "home
mobile node (the home agent did not already have a Binding Cache registration" to indicate that the node is serving as a home
entry for this home address marked as a "home registration"), then agent for this binding. Binding Cache entries marked as a "home
the home agent MUST multicast onto the home link a "gratuitous" registration" MUST be excluded from the normal cache replacement
Neighbor Advertisement message [11] on behalf of the mobile node, in policy used for the Binding Cache (Section 8.7) and MUST NOT be
order to begin intercepting packets addressed to it while it is away removed from the Binding Cache until the expiration of the Lifetime
from home. Specifically, the home agent follows the following steps: period.
- The home agent examines the value of the Prefix Length field in The lifetime for the Binding Cache entry MUST NOT be greater than the
the Binding Update. If this value is zero, the following step remaining valid lifetime for the subnet prefix in the mobile node's
is carried out only for the individual home address specified home address specified with the Binding Update. The remaining valid
(in the Home Address option in the packet) for this binding. lifetime for this prefix is determined by the home agent based on
If, instead, this field is nonzero, then the following step is its own Prefix List entry for this prefix [13]. If the value of the
carried out for each address for the mobile node formed from Lifetime field specified by the mobile node in its Binding Update is
the interface identifier in the mobile node's home address in greater than this prefix lifetime, the home agent MUST decrease the
this Binding Update (the remaining low-order bits in the address binding lifetime to less than or equal to the prefix valid lifetime.
after the indicated subnet prefix), together with each one of The home agent MAY further decrease the specified lifetime for the
the subnet prefixes currently considered by the home agent to be binding, for example based on a local policy implemented by the home
on-link (including both the link-local and site-local prefix). agent. The resulting lifetime is stored by the home agent in the
Binding Cache entry, and this Binding Cache entry MUST be deleted by
the home agent after the expiration of this lifetime.
- For each specific IP address for the mobile node determined in The Prefix Length in the Binding Update MUST also be saved in the
the first step above, the home agent multicast onto the home link Binding Cache entry.
(to the all-nodes multicast address) a Neighbor Advertisement
message [11] on behalf of the mobile node, to advertise the
home agent's own link-layer address for this IP address. The
Target Address in the Neighbor Advertisement message MUST be set
to this IP address for the mobile node, and the Advertisement
MUST include a Target Link-layer Address option specifying the
home agent's link-layer address. The Solicited Flag (S) in the
Advertisement MUST NOT be set, since it was not solicited by any
Neighbor Solicitation message. The Override Flag (O) in the
Advertisement MUST be set, indicating that the Advertisement
SHOULD override any existing Neighbor Cache entry at any node
receiving it.
Any node on the home link receiving one of the Neighbor Advertisement If the Acknowledge (A) bit is set in the Binding Update (it SHOULD
messages described above will thus update its Neighbor Cache to be), then the home agent MUST return a Binding Acknowledgement to the
associate the mobile node's address with the home agent's link mobile node, constructed as follows:
layer address, causing it to transmit any future packets for the
mobile node normally destined to this address instead to the mobile
node's home agent. Since multicasts on the local link (such as
Ethernet) are typically not guaranteed to be reliable, the home
agent MAY retransmit this Neighbor Advertisement message up to
MAX_ADVERT_REXMIT times to increase its reliability. It is still
possible that some nodes on the home link will not receive any of
these Neighbor Advertisements, but these nodes will eventually be
able to detect the link-layer address change for the mobile node's
home address, through use of Neighbor Unreachability Detection [11].
In addition, while this node is serving as a home agent for this - The Status field MUST be set to a value indicating success (the
mobile node (it still has a "home registration" entry for this mobile value MUST be less than 128). The only currently defined success
node in its Binding Cache), it MUST act as a proxy for this mobile Status value is 0, indicating simply that the Binding Update was
node to reply to any received Neighbor Solicitation messages for accepted.
it. When a home agent receives a Neighbor Solicitation message, it
MUST check if the Target Address specified in the message matches
the home address of any mobile node for which it has a Binding
Cache entry marked as a "home registration". This check MUST
include all possible home addresses for the mobile node, based on
the subnet prefixes currently considered to be on-link by the home
agent (including the corresponding link-local address and site-local
address), if the Prefix Length field was nonzero in the Binding
Update that created this "home registration" binding at the home
agent. If such an entry exists in the home agent's Binding Cache,
the home agent MUST reply to the Neighbor Solicitation message
with a Neighbor Advertisement message, giving the home agent's own
link-layer address as the link-layer address for the specified
Target Address. Acting as a proxy in this way allows other nodes on
the mobile node's home link to resolve the mobile node's IPv6 home
address, and allows the home agent to to defend these addresses on
the home link for Duplicate Address Detection [11].
Any packet addressed to the mobile node's home address (including - The Sequence Number field MUST be copied from the Sequence Number
addresses formed from other on-link prefixes, if the Prefix Length given in the Binding Update.
field was nonzero in the Binding Update) will thus be received by the
mobile node's home agent while the mobile node is registered away
from home. For any such packet received by the home agent for the
mobile node, the home agent SHOULD tunnel the packet to the mobile
node at its primary care-of address, as described in Section 9.5.
However, packets addressed to the mobile node's link-local address - The Lifetime field MUST be set to the remaining lifetime for
MUST NOT be tunneled to the mobile node. Instead, such a packet MUST the binding as set by the home agent in its "home registration"
be discarded, and the home agent SHOULD return an ICMP Destination Binding Cache entry for the mobile node. As described above,
Unreachable, Code 3, message to the packet's Source Address (unless this lifetime MUST NOT be greater than the remaining valid
this Source Address is a multicast address). lifetime for the subnet prefix in the mobile node's home address.
Similarly, packets addressed to the mobile node's site-local address - The Refresh field MUST be set to a value less than or equal to
MUST NOT be tunneled to the mobile node, unless the mobile node's the Lifetime value being returned in the Binding Update. If the
registered primary care-of address is within the same site as the home agent stores the Binding Cache entry in nonvolatile storage
mobile node's home address. For any such packet not forwarded to the (that survives the crash or other failure of the home agent),
mobile node for this reason, the packet MUST be discarded, and the then the Refresh field SHOULD be set to the same value as the
home agent SHOULD return an ICMP Destination Unreachable, Code 3, Lifetime field; otherwise, the home agent MAY set the Refresh
message to the packet's Source Address (unless this Source Address is field to a value less than the Lifetime field, to indicate that
a multicast address). Currently, however, the exact definition and the mobile node SHOULD attempt to refresh its home registration
semantics of a "site" are undefined in IPv6, and the mechanism for at the indicated shorter interval (although the home agent will
a home agent to determine if the care-of address is within the same still retain the registration for the Lifetime period, even if
site as the home address is outside the scope of this document. the mobile node does not refresh its registration within the
Refresh period).
In addition, the home agent MUST follow the procedure defined in
Section 9.5 to intercept packets on the mobile node's home link
addressed to the mobile node, while the home agent is serving as the
home agent for this mobile node.
9.4. Primary Care-of Address De-registration 9.4. Primary Care-of Address De-registration
General processing of a received Binding Update that requests a When a node receives a Binding Update, it MUST validate it and
binding to be deleted, is described in Section 8.4. However, if determine the type of Binding Update according to the steps described
the Home Registration (H) bit is set in the Binding Update, then in Section 8.2. This section describes the processing of a valid
after following the step outlined for all Binding Update options in Binding Update that requests the receiving node to no longer serve as
Section 8.2, the receiving node MUST process the Binding Update as its home agent, de-registering its primary care-of address.
specified in this section rather than following the general procedure
for requests to delete a cache binding specified in Section 8.4.
To begin processing the Binding Update, the home agent MUST perform To begin processing the Binding Update, the home agent MUST perform
the following sequence of tests: the following test:
- If the node is not a router that implements home agent
functionality, then the node MUST reject the Binding Update and
SHOULD return a Binding Acknowledgement to the mobile node, in
which the Status field is set to 132 (home registration not
supported).
- Else, if the home address for the binding (the Home Address - If the receiving node has no entry in its Binding Cache for this
field in the packet's Home Address option) is not an on-link mobile node that is marked as a "home registration", then this
IPv6 address with respect to the home agent's current Prefix node MUST reject the Binding Update and SHOULD return a Binding
List, then it MUST reject the Binding Update and SHOULD return a Acknowledgement to the mobile node, in which the Status field is
Binding Acknowledgement to the mobile node, in which the Status set to 137 (not home agent for this mobile node).
field is set to 133 (not home subnet).
If the home agent does not reject the Binding Update as described If the home agent does not reject the Binding Update as described
above, then it MUST delete any existing entry in its Binding Cache above, then it MUST delete any existing entry in its Binding Cache
for this mobile node. for this mobile node.
9.5. Tunneling Intercepted Packets to a Mobile Node If the Acknowledge (A) bit is set in the Binding Update (it SHOULD
be), then the home agent MUST return a Binding Acknowledgement to the
mobile node, constructed as follows:
- The Status field MUST be set to a value indicating success (the
value MUST be less than 128). The only currently defined success
Status value is 0, indicating simply that the Binding Update was
accepted.
- The Sequence Number field MUST be copied from the Sequence Number
given in the Binding Update.
- The Lifetime field MUST be set to zero.
- The Refresh field MUST be set to zero.
In addition, the home agent MUST stop intercepting packets on the
mobile node's home link addressed to the mobile node (Section 9.5).
9.5. Intercepting Packets for a Mobile Node
While a node is serving as the home agent for mobile node (while the
node has an entry in its Binding Cache for this mobile node that is
marked as a "home registration"), this node MUST attempt to intercept
packets on the mobile node's home link addressed to the mobile node,
and MUST tunnel each intercepted packet to the mobile node using
using IPv6 encapsulation [4].
In order to intercept such packets on the home link, when a node
becomes the home agent for some mobile node (it did not already
have a Binding Cache entry for this mobile node marked as a "home
registration"), then the home agent MUST multicast onto the home link
a "gratuitous" Neighbor Advertisement message [13] on behalf of the
mobile node. Specifically, the home agent performs the following
steps:
- The home agent examines the value of the Prefix Length field
in the new "home registration" Binding Cache entry. If this
value is zero, the following step is carried out only for the
individual home address specified for this binding. If, instead,
this field is nonzero, then the following step is carried out
for each address for the mobile node formed from the interface
identifier in the mobile node's home address in this binding
(the remaining low-order bits in the address after the indicated
subnet prefix), together with each one of the subnet prefixes
currently considered by the home agent to be on-link (including
both the link-local and site-local prefix).
- For each specific IP address for the mobile node determined
in the first step above, the home agent multicasts onto the
home link (to the all-nodes multicast address) a Neighbor
Advertisement message [13] on behalf of the mobile node, to
advertise the home agent's own link-layer address for this IP
address. The Target Address in the Neighbor Advertisement
message MUST be set to this IP address for the mobile node, and
the Advertisement MUST include a Target Link-layer Address option
specifying the home agent's link-layer address. The Solicited
Flag (S) in the Advertisement MUST NOT be set, since it was not
solicited by any Neighbor Solicitation message. The Override
Flag (O) in the Advertisement MUST be set, indicating that the
Advertisement SHOULD override any existing Neighbor Cache entry
at any node receiving it.
Any node on the home link receiving one of the Neighbor Advertisement
messages described above will thus update its Neighbor Cache to
associate the mobile node's address with the home agent's link
layer address, causing it to transmit any future packets for the
mobile node normally destined to this address instead to the mobile
node's home agent. Since multicasts on the local link (such as
Ethernet) are typically not guaranteed to be reliable, the home
agent MAY retransmit this Neighbor Advertisement message up to
MAX_ADVERT_REXMIT times to increase its reliability. It is still
possible that some nodes on the home link will not receive any of
these Neighbor Advertisements, but these nodes will eventually be
able to detect the link-layer address change for the mobile node's
home address, through use of Neighbor Unreachability Detection [13].
While a node is serving as a home agent for some mobile node (it
still has a "home registration" entry for this mobile node in its
Binding Cache), the home agent uses IPv6 Neighbor Discovery [13]
to intercept unicast packets on the home link addressed the mobile
node's home address. In order to intercept packets in this way,
the home agent MUST act as a proxy for this mobile node to reply to
any received Neighbor Solicitation messages for it. When a home
agent receives a Neighbor Solicitation message, it MUST check if the
Target Address specified in the message matches the home address
of any mobile node for which it has a Binding Cache entry marked
as a "home registration". This check MUST include all possible
home addresses for the mobile node, based on the subnet prefixes
currently considered to be on-link by the home agent (including the
corresponding link-local address and site-local address), if the
Prefix Length in the Binding Cache entry for this mobile node (from
the Binding Update that created this Cache entry) is nonzero.
If such an entry exists in the home agent's Binding Cache, the home
agent MUST reply to the Neighbor Solicitation message with a Neighbor
Advertisement message, giving the home agent's own link-layer address
as the link-layer address for the specified Target Address. Acting
as a proxy in this way allows other nodes on the mobile node's home
link to resolve the mobile node's IPv6 home address, and allows
the home agent to to defend these addresses on the home link for
Duplicate Address Detection [13].
9.6. Tunneling Intercepted Packets to a Mobile Node
For any packet sent to a mobile node from the mobile node's home For any packet sent to a mobile node from the mobile node's home
agent (for which the home agent is the original sender of the agent (for which the home agent is the original sender of the
packet), the home agent is operating as a correspondent node of packet), the home agent is operating as a correspondent node of
the mobile node for this packet and the procedures described in the mobile node for this packet and the procedures described in
Section 8.9 apply. The home agent (as a correspondent node) uses a Section 8.9 apply. The home agent (as a correspondent node) uses a
Routing header to route the packet to the mobile node by way of the Routing header to route the packet to the mobile node by way of the
care-of address in the home agent's Binding Cache (the mobile node's care-of address in the home agent's Binding Cache (the mobile node's
primary care-of address, in this case). primary care-of address, in this case).
In addition, while the mobile node is away from home and this node is While the mobile node is away from home and this node is acting
acting as the mobile node's home agent, the home agent intercepts any as the mobile node's home agent, the home agent intercepts any
packets on the home link addressed to the mobile node's home address, packets on the home link addressed to the mobile node's home address
as described in Section 9.3. The home agent cannot use a Routing (including addresses formed from other on-link prefixes, if the
header to forward these intercepted packets to the mobile node, Prefix Length field was nonzero in the Binding Update), as described
since it cannot modify the packet in flight without invalidating any in Section 9.5. The home agent cannot use a Routing header to
existing IPv6 Authentication header present in the packet [7]. forward these intercepted packets to the mobile node, since it cannot
modify the packet in flight without invalidating any existing IPv6
AH [8] or ESP [9] header present in the packet.
For forwarding each intercepted packet to the mobile node, the For forwarding each intercepted packet to the mobile node, the
home agent MUST tunnel the packet to the mobile node using IPv6 home agent MUST tunnel the packet to the mobile node using IPv6
encapsulation [4]; the tunnel entry point node is the home agent, encapsulation [4]; the tunnel entry point node is the home agent,
and the tunnel exit point node is the mobile node itself (using its and the tunnel exit point node is the primary care-of address as
primary care-of address as registered with the home agent). When a registered with the home agent (which is an address of the mobile
home agent encapsulates an intercepted packet for forwarding to the node itself). When a home agent encapsulates an intercepted packet
mobile node, the home agent sets the Source Address in the prepended for forwarding to the mobile node, the home agent sets the Source
tunnel IP header to the home agent's own IP address, and sets the Address in the prepended tunnel IP header to the home agent's own IP
Destination Address in the tunnel IP header to the mobile node's address, and sets the Destination Address in the tunnel IP header
primary care-of address. When received by the mobile node (using its to the mobile node's primary care-of address. When received by the
primary care-of address), normal processing of the tunnel header [4] mobile node (using its primary care-of address), normal processing of
will result in decapsulation and processing of the original packet by the tunnel header [4] will result in decapsulation and processing of
the mobile node. the original packet by the mobile node.
9.6. Renumbering the Home Subnet However, packets addressed to the mobile node's link-local address
MUST NOT be tunneled to the mobile node. Instead, such a packet MUST
be discarded, and the home agent SHOULD return an ICMP Destination
Unreachable, Code 3, message to the packet's Source Address (unless
this Source Address is a multicast address). Packets addressed to
the mobile node's site-local address SHOULD be tunneled to the mobile
node by default, but this behavior MUST be configurable to disable
it; currently, the exact definition and semantics of a "site" and a
site-local address are undefined in IPv6, and this default behavior
might change at some point in the future.
Neighbor Discovery [11] specifies a mechanism by which all nodes on a Tunneling of multicast packets to a mobile node follows similar
subnet can gracefully autoconfigure new addresses, say by each node limitations to those defined above for unicast packets addressed to
combining a new subnet prefix with its existing link-layer address. the mobile node's link-local and site-local addresses. Multicast
As currently specified, this mechanism works when the nodes are on packets addressed to a multicast address with link-local scope [7],
the same link as the router issuing the necessary multicast packets to which the mobile node is subscribed, MUST NOT be tunneled
to advertise the new subnet prefix(es) appropriate for the link. to the mobile node; such packets SHOULD be silently discarded
(after delivering to other local multicast recipients). Multicast
packets addressed to a multicast address with scope larger
than link-local but smaller than global (e.g., site-local and
organization-local) [7], to which the mobile node is subscribed,
SHOULD be tunneled to the mobile node by default, but this behavior
MUST be configurable to disable it; this default behavior might
change at some point in the future as the definition of these scopes
become better defined in IPv6.
However, for mobile nodes away from home, special care must be taken 9.7. Renumbering the Home Subnet
to allow the mobile nodes to renumber gracefully. The most direct
method of ensuring this is for the home agent to encapsulate and
tunnel the multicast packets to the primary care-of address of each
mobile node for which it is serving as the home agent. The rules for
this are as follows:
- A mobile node assumes that its subnet prefix has not changed IPv6 provides mechanisms through Neighbor Discovery [13] and Address
unless it receives an authenticated Router Advertisement message Autoconfiguration [22] to aid in renumbering a subnet, such as when a
from its home agent that the prefix has changed. site switches to a new network service provider. In renumbering, new
prefixes and addresses can be introduced for the subnet and old ones
can be deprecated and removed. These mechanisms are defined to work
while all nodes using the old prefixes are at home, connected to the
link using these prefixes. Mobile IPv6 extends these mechanisms for
the case in which one or more mobile nodes using the old prefixes are
away from home while the renumbering takes place.
- When the mobile node is at home, the home agent does not tunnel The IPv6 renumbering mechanisms are based on nodes on the link
Router Advertisements to it. receiving Prefix Information options in Router Advertisement messages
giving the valid lifetime and preferred lifetime for different
prefixes on the link [13]. Mobile IPv6 arranges to tunnel certain
Router Advertisements giving "important" Prefix Information options
to mobile nodes while away from home. To avoid the need to tunnel
all Router Advertisements from the home link to a mobile node away
from home, those Router Advertisements that are tunneled to the
mobile node are retransmitted until acknowledged. To avoid possible
security attacks from forged Router Advertisements tunneled to
the mobile node, all such tunneled Router Advertisements must be
authenticated to the mobile node by its home agent using AH [8] or
ESP [9].
- The mobile node's home agent serves as a proxy for the mobile Specifically, a home agent serving some mobile node SHOULD construct
node's home address and link-local address, including defending and tunnel to the mobile node a new Router Advertisement when any of
these addresses for Duplicate Address Detection, while the mobile the following conditions occur:
node is registered with the home agent away from home.
- When a home subnet prefix changes, the home agent tunnels Router - The preferred or valid lifetime for an existing prefix on the
Advertisement packets to each mobile node registered with it that home link is reduced.
is currently away from home and using a home address with the
affected subnet prefix. Such tunneled Router Advertisements MUST
be authenticated [7].
- When a mobile node receives a tunneled Router Advertisement - A new prefix is introduced on the home link.
containing a new subnet prefix, it MUST perform the standard
autoconfiguration operation to create its new address.
- When a mobile node returns to its home link, it must again - The state of the home agent's AdvManagedFlag flag [13] changes
perform Duplicate Address Detection at the earliest possible from FALSE to TRUE or from TRUE to FALSE.
moment after it has deleted its "home registration" binding with
its home agent.
- A mobile node MAY send a Router Solicitation to its home agent at The home agent determines these conditions based on its own
any time, within the constraints imposed by rate control defined configuration as a router and based on the Router Advertisements
by Neighbor Discovery [11]. that it receives on the home link. The home agent constructs a new
Router Advertisement message containing no options other than the
Prefix Information options describing the prefixes for which one of
the conditions above has occurred since the last Router Advertisement
tunneled to and acknowledged by the mobile node. When multiple
conditions occur at or near the same time, the home agent SHOULD
attempt to combine them into a single Router Advertisement message to
the mobile node.
In tunneling each such Router Advertisement to the mobile node, the
home agent MUST construct the packet as follows:
- The Source Address in the packet's IPv6 header MUST be set to the
home agent's IP address to which the mobile node addressed its
current home registration.
- The packet MUST include either an AH [8] or ESP [9] header
providing sender authentication, data integrity protection, and
replay protection.
- The packet MUST include a Binding Request destination option.
- The packet MUST be tunneled to the mobile node's primary care-of
address using a Routing header, in the same way as any packet
sent to the mobile node originated by the home agent (rather than
using IPv6 encapsulation, as would be used by the home agent for
intercepted packets).
The home agent SHOULD periodically continue to retransmit this
tunneled packet to the mobile node, until it is acknowledged by the
receipt from the mobile node of a Binding Update matching the Binding
Request in the packet (i.e., with matching Sequence Number). If
while the mobile node is still retransmitting a Router Advertisement
to the mobile node, another condition as described above occurs on
the home link causing another Router Advertisement to be tunneled to
the mobile node, the home agent SHOULD combine any Prefix Information
options in the unacknowledged Router Advertisement into the new
Router Advertisement and then begin retransmitting the new Router
Advertisement rather than the old one.
In addition, as described in Section 9.3, the lifetime returned by a
mobile node's home agent in its Binding Acknowledgement in response
to registration of a new primary care-of address by the mobile node
MUST be no greater than the remaining valid lifetime for the subnet
prefix in the mobile node's home address. Furthermore, as described
in Section 10.7, Binding Updates sent by the mobile node to other
nodes MUST use a lifetime no greater than the remaining lifetime of
its home registration of its primary care-of address. These limits
on a binding lifetimes ensure that no node uses a mobile node's home
address beyond the time that it becomes invalid. The mobile node
SHOULD further limit the lifetimes that it sends on any Binding
Updates to be within the remaining preferred lifetime for the prefix
in its home address.
10. Mobile Node Operation 10. Mobile Node Operation
10.1. Sending Packets While Away from Home 10.1. Sending Packets While Away from Home
While a mobile node is away from home, it continues to use its home While a mobile node is away from home, it continues to use its home
address as well as also using one or more care-of addresses. When address as well as also using one or more care-of addresses. When
sending a packet while away from home, a mobile node MAY choose among sending a packet while away from home, a mobile node MAY choose among
these in selecting the address that it will use as the source of the these in selecting the address that it will use as the source of the
packet, as follows: packet, as follows:
skipping to change at page 46, line 30 skipping to change at page 60, line 30
Doing so also makes the node's mobility and the fact that it is Doing so also makes the node's mobility and the fact that it is
currently away from home transparent to the correspondent nodes currently away from home transparent to the correspondent nodes
with which it communicates. For packets sent that are part of with which it communicates. For packets sent that are part of
transport-level connections established while the mobile node transport-level connections established while the mobile node
was at home, the mobile node MUST use its home address in this was at home, the mobile node MUST use its home address in this
way. Likewise, for packets sent that are part of transport-level way. Likewise, for packets sent that are part of transport-level
connections that the mobile node may still be using after moving connections that the mobile node may still be using after moving
to a new location, the mobile node SHOULD use its home address to a new location, the mobile node SHOULD use its home address
in this way. When sending such packets, Mobile IP will modify in this way. When sending such packets, Mobile IP will modify
the packet to move the home address into a Home Address option the packet to move the home address into a Home Address option
and will set the IPv6 header's Source Address field to one of the and will set the IPv6 header's Source Address field to one of
mobile node's care-of address; these modifications to the packet the mobile node's care-of addresses; these modifications to
are then reversed in the node receiving the packet, restoring the packet are then reversed in the node receiving the packet,
the mobile node's home address to be the packet's Source Address restoring the mobile node's home address to be the packet's
before processing by higher protocols layers and applications. Source Address before processing by higher protocol layers and
applications.
- For short-term communication, particularly for communication that - For short-term communication, particularly for communication that
may easily be retried if it fails, the mobile node MAY choose to may easily be retried if it fails, the mobile node MAY choose
directly use one of its care-of addresses as the source of the to directly use one of its care-of addresses as the source of
packet, thus not requiring the use of a Home Address option in the packet, thus not requiring the use of a Home Address option
the packet. An example of this type of communication might be in the packet. An example of this type of communication might
DNS queries sent by the mobile node [9, 10]. Using the mobile be DNS queries sent by the mobile node [11, 12]. Using the
node's care-of address as the source for such queries will mobile node's care-of address as the source for such queries will
generally have a lower overhead than using the mobile node's generally have a lower overhead than using the mobile node's
home address, since no extra options need be used in either the home address, since no extra options need be used in either the
query or its reply, and all packets can be routed normally, query or its reply, and all packets can be routed normally,
directly between their source and destination without relying directly between their source and destination without relying
on Mobile IP. If the mobile node has no particular knowledge on Mobile IP. If the mobile node has no particular knowledge
that the communication being sent fits within this type of that the communication being sent fits within this general type
communication, however, the mobile node SHOULD NOT use its of communication, however, the mobile node SHOULD NOT use its
care-of address as the source of the packet in this way. care-of address as the source of the packet in this way.
If the mobile node uses one of its care-of addresses as the source If the mobile node uses one of its care-of addresses as the source
of some packet while away from home, no special Mobile IP processing of some packet while away from home, no special Mobile IP processing
is required for sending this packet. The packet is simply addressed is required for sending this packet. The packet is simply addressed
and transmitted in the same way as any normal IPv6 packet, setting and transmitted in the same way as any normal IPv6 packet, setting
the Source Address field in the packet's IPv6 header to this care-of the Source Address field in the packet's IPv6 header to this care-of
address. address.
On the other hand, if while away from home, the mobile node uses its On the other hand, if while away from home, the mobile node uses its
skipping to change at page 47, line 41 skipping to change at page 61, line 42
- Change the Source Address field in the packet's IPv6 header to - Change the Source Address field in the packet's IPv6 header to
one of the mobile node's care-of addresses. This will typically one of the mobile node's care-of addresses. This will typically
be the mobile node's current primary care-of address, but MUST be the mobile node's current primary care-of address, but MUST
be a care-of address with a subnet prefix that is on-link on the be a care-of address with a subnet prefix that is on-link on the
network interface on which the mobile node will transmit the network interface on which the mobile node will transmit the
packet. packet.
This addition of the Home Address option to a packet MUST be This addition of the Home Address option to a packet MUST be
performed before outgoing IPsec processing, such as the addition of performed before outgoing IPsec processing, such as the addition of
an AH [7] or ESP [8] header to the packet, is performed. Likewise, an AH [8] or ESP [9] header to the packet, is performed. Likewise,
IPsec processing for a received packet containing a Home Address IPsec processing for a received packet containing a Home Address
option MUST be performed before the packet is possibly modified as option MUST be performed before the packet is possibly modified as
part of processing the Home Address option. By using the care-of part of processing the Home Address option. By using the care-of
address as the Source Address in the IPv6 header, with the mobile address as the Source Address in the IPv6 header, with the mobile
node's home address instead in the Home Address option, the packet node's home address instead in the Home Address option, the packet
will be able to safely pass through any router implementing ingress will be able to safely pass through any router implementing ingress
filtering [6]. filtering [6].
10.2. Movement Detection 10.2. Receiving Packets While Away from Home
While away from home, a mobile node will receive packets addressed to
its home address, by one of three methods:
- Packets sent by a correspondent node that does not have a
Binding Cache entry for the mobile node, will be sent by the
correspondent node in the same way as any normal IP packet. Such
packets will then be intercepted by the mobile node's home agent,
encapsulated using IPv6 encapsulation [4], and tunneled to the
mobile node's primary care-of address.
- Packets sent by a correspondent node that has a Binding Cache
entry for the mobile node that contains the mobile node's current
care-of address, will be sent by the correspondent node using
a Routing header. The packet will be addressed to the mobile
node's care-of address, with the final hop in the Routing header
directing the packet to the mobile node's home address; the
processing of this last hop of the Routing header is entirely
internal to the mobile node, since the care-of address and home
address are both addresses within the mobile node.
- Packets sent by a correspondent node that has a Binding Cache
entry for the mobile node that contains an out-of-date care-of
address for the mobile node, will be sent by the correspondent
node using a Routing header, as described above. If the mobile
node sent a Binding Update to its previous default router when
moving from this care-of address to another, and if the Binding
Cache entry that was created from this Binding Update is still
present in this router's Binding Cache, then such a packet
will be intercepted by this router, encapsulated using IPv6
encapsulation [4], and tunneled to the mobile node's primary
care-of address (registered with this router, acting as a home
agent for this out-of-date care-of address).
For packets received by either the first or last of these three
methods, the mobile node SHOULD send a Binding Update to the original
sender of the packet, as described in Section 10.7, subject to the
rate limiting defined in Section 10.10. The mobile node SHOULD
also process the received packet in the manner defined for IPv6
encapsulation [4], which will result in the encapsulated (inner)
packet being processed normally by upper-layer protocols within the
mobile node, as if it had been addressed (only) to the mobile node's
home address.
For packets received by the second method above (using a Routing
header), the mobile node SHOULD process the received packet in the
manner defined for the type of IPv6 Routing header used [5], which
will result in the packet being processed normally by upper-layer
protocols within the mobile node, as if it had been addressed (only)
to the mobile node's home address.
In addition, the general procedures defined by IPv6 for Routing
headers suggest that a received Routing header MAY be automatically
"reversed" to construct a Routing header for use in any response
packets sent by upper-layer protocols, if the received packet is
authenticated [5]. If this is done for upper-layer protocol response
packets sent by a mobile node while away from home, the mobile
node SHOULD NOT include its own care-of address, which appears in
the Routing header of the received packet, in the reversed route
for the response packet. If the received Routing header contained
no additional hops (other than the mobile node's home address and
care-of address), then any upper-layer protocol response packet
SHOULD NOT include a Routing header.
10.3. Movement Detection
A mobile node MAY use any combination of mechanisms available to it A mobile node MAY use any combination of mechanisms available to it
to detect when it has moved from one link to another. The primary to detect when it has moved from one link to another. The primary
movement detection mechanism for Mobile IPv6 defined here uses the movement detection mechanism for Mobile IPv6 defined here uses the
facilities of IPv6 Neighbor Discovery, including Router Discovery and facilities of IPv6 Neighbor Discovery, including Router Discovery and
Neighbor Unreachability Detection. The description here is based on Neighbor Unreachability Detection. The description here is based on
the conceptual model of the organization and data structures defined the conceptual model of the organization and data structures defined
by Neighbor Discovery [11]. by Neighbor Discovery [13].
Mobile nodes SHOULD use Router Discovery to discover new routers and Mobile nodes SHOULD use Router Discovery to discover new routers and
on-link subnet prefixes; a mobile node MAY send Router Solicitation on-link subnet prefixes; a mobile node MAY send Router Solicitation
messages, or MAY wait for unsolicited (periodic) Router Advertisement messages, or MAY wait for unsolicited (periodic) multicast Router
messages, as specified for Router Discovery [11]. Based on received Advertisement messages, as specified for Router Discovery [13].
Router Advertisement messages, a mobile node (in the same way as any Based on received Router Advertisement messages, a mobile node (in
other node) maintains an entry in its Default Router List for each the same way as any other node) maintains an entry in its Default
router, and an entry in its Prefix List for each subnet prefix, that Router List for each router, and an entry in its Prefix List for each
it currently considers to be on-link. Each entry in these lists has subnet prefix, that it currently considers to be on-link. Each entry
an associated invalidation timer value (extracted from the Router in these lists has an associated invalidation timer value (extracted
Advertisement) used to expire the entry when it becomes invalid. from the Router Advertisement) used to expire the entry when it
becomes invalid.
While away from home, a mobile node SHOULD select one router from While away from home, a mobile node SHOULD select one router from
its Default Router List to use as its default router, and one subnet its Default Router List to use as its default router, and one subnet
prefix advertised by that router from its Prefix List to use as prefix advertised by that router from its Prefix List to use as
the subnet prefix in its primary care-of address. A mobile node the subnet prefix in its primary care-of address. A mobile node
MAY also have associated additional care-of addresses, using other MAY also have associated additional care-of addresses, using other
subnet prefixes from its Prefix List. The method by which a mobile subnet prefixes from its Prefix List. The method by which a mobile
node selects and forms a care-of address from the available subnet node selects and forms a care-of address from the available subnet
prefixes is described in Section 10.3. The mobile node registers prefixes is described in Section 10.4. The mobile node registers
its primary care-of address with its home agent, as described in its primary care-of address with its home agent, as described in
Section 10.4. Section 10.5.
While a mobile node is away from home and using some router as its While a mobile node is away from home and using some router as its
default router, it is important for the mobile node to be able to default router, it is important for the mobile node to be able to
quickly detect when that router becomes unreachable, so that it can quickly detect when that router becomes unreachable, so that it can
switch to a new default router and to a new primary care-of address. switch to a new default router and to a new primary care-of address.
Since some links (notably wireless) do not necessarily work equally Since some links (notably wireless) do not necessarily work equally
well in both directions, it is likewise important for the mobile well in both directions, it is likewise important for the mobile
node to detect when it becomes unreachable to packets sent from its node to detect when it becomes unreachable to packets sent from its
default router, so that the mobile node can take steps to ensure that default router, so that the mobile node can take steps to ensure that
any correspondent nodes attempting to communicate with it can still any correspondent nodes attempting to communicate with it can still
reach it through some other route. reach it through some other route.
To detect when its default router becomes unreachable, a mobile To detect when its default router becomes unreachable, a mobile
node SHOULD use Neighbor Unreachability Detection. As specified in node SHOULD use Neighbor Unreachability Detection. As specified in
Neighbor Discovery [11], while the mobile node is actively sending Neighbor Discovery [13], while the mobile node is actively sending
packets to (or through) its default router, the mobile node can packets to (or through) its default router, the mobile node can
detect that the router (as its neighbor) is still reachable either detect that the router (as its neighbor) is still reachable either
through indications from upper layer protocols on the mobile node through indications from upper layer protocols on the mobile node
that a connection is making "forward progress" (e.g., receipt of TCP that a connection is making "forward progress" (e.g., receipt of TCP
acknowledgements for new data transmitted), or through receipt of a acknowledgements for new data transmitted), or through receipt of a
Neighbor Advertisement message from its default router in response Neighbor Advertisement message from its default router in response
to an explicit Neighbor Solicitation messages to it. Note that to an explicit Neighbor Solicitation messages to it. Note that
although this mechanism only detects that the mobile node's default although this mechanism detects that the mobile node's default router
router has become unreachable to the mobile node while the mobile has become unreachable to the mobile node only while the mobile node
node is actively sending packets to it, this is the only time that is actively sending packets to it, this is the only time that this
this direction of reachability confirmation is needed. Confirmation direction of reachability confirmation is needed. Confirmation
that the mobile node is still reachable from the router is handled that the mobile node is still reachable from the router is handled
separately, as described below. separately, as described below.
For a mobile node to detect when it has become unreachable to its For a mobile node to detect when it has become unreachable from its
default router, however, the mobile node cannot efficiently rely on default router, the mobile node cannot efficiently rely on Neighbor
Neighbor Unreachability Detection alone, since the network overhead Unreachability Detection alone, since the network overhead would be
would be prohibitively high in many cases for a mobile node to prohibitively high in many cases for a mobile node to continually
continually probe its default router with Neighbor Solicitation probe its default router with Neighbor Solicitation messages even
messages even when it is not otherwise actively sending packets to when it is not otherwise actively sending packets to it. Instead,
it. Instead, a mobile node SHOULD consider receipt of any IPv6 a mobile node SHOULD consider receipt of any IPv6 packets from its
packets from its current default router as an indication that it is current default router as an indication that it is still reachable
still reachable from the router. Both packets from the router's IP from the router. Both packets from the router's IP address and
address and (IPv6) packets from its link-layer address (e.g., those (IPv6) packets from its link-layer address (e.g., those forwarded but
forwarded but not originated by the router) SHOULD be considered. not originated by the router) SHOULD be considered.
Since the router SHOULD be sending periodic multicast Router Since the router SHOULD be sending periodic unsolicited multicast
Advertisement messages, the mobile node will have frequent Router Advertisement messages, the mobile node will have frequent
opportunity to check if it is still reachable from its default opportunity to check if it is still reachable from its default
router, even in the absence of other packets to it from the router. router, even in the absence of other packets to it from the router.
If Router Advertisements that the mobile node receives include If Router Advertisements that the mobile node receives include
an Advertisement Interval option, the mobile node MAY use its an Advertisement Interval option, the mobile node MAY use its
Advertisement Interval field as an indication of the frequency with Advertisement Interval field as an indication of the frequency with
which it should expect to continue to receive future Advertisements which it should expect to continue to receive future Advertisements
from that router. This field specifies the minimum rate (the maximum from that router. This field specifies the minimum rate (the maximum
amount of time between successive Advertisements) that the mobile amount of time between successive Advertisements) that the mobile
node should expect. If this amount of time elapses without the node should expect. If this amount of time elapses without the
mobile node receiving any Advertisement from this router, the mobile mobile node receiving any Advertisement from this router, the mobile
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has been lost. It is thus possible for the mobile node to implement has been lost. It is thus possible for the mobile node to implement
its own policy for determining the number of Advertisements from its own policy for determining the number of Advertisements from
its current default router it is willing to tolerate losing before its current default router it is willing to tolerate losing before
deciding to switch to a different router from which it may currently deciding to switch to a different router from which it may currently
be correctly receiving Advertisements. be correctly receiving Advertisements.
On some types of network interfaces, the mobile node MAY also On some types of network interfaces, the mobile node MAY also
supplement this monitoring of Router Advertisements, by setting its supplement this monitoring of Router Advertisements, by setting its
network interface into "promiscuous" receive mode, so that it is able network interface into "promiscuous" receive mode, so that it is able
to receive all packets on the link, including those not link-level to receive all packets on the link, including those not link-level
addressed to it. The mobile node will then be able to detect any addressed to it (i.e., disabling link-level address filtering). The
packets sent by the router, in order to to detect reachability from mobile node will then be able to detect any packets sent by the
the router. This use of promiscuous mode may be useful on very low router, in order to to detect reachability from the router. This
bandwidth (e.g., wireless) links, but its use MUST be configurable on use of promiscuous mode may be useful on very low bandwidth (e.g.,
the mobile node. wireless) links, but its use MUST be configurable on the mobile node.
If the above means do not provide indication that the mobile node If the above means do not provide indication that the mobile node is
is still reachable from its current default router (i.e., the still reachable from its current default router (i.e., the mobile
mobile node receives no packets from the router for a period of node receives no packets from the router for a period of time), then
time), then the mobile node SHOULD actively probe the router with the mobile node SHOULD attempt to actively probe the router with
Neighbor Solicitation messages, even if it is not otherwise actively Neighbor Solicitation messages, even if it is not otherwise actively
sending packets to the router. If it receives a solicited Neighbor sending packets to the router. If it receives a solicited Neighbor
Advertisement message in response from the router, then the mobile Advertisement message in response from the router, then the mobile
node can deduce that it is still reachable. It is expected that the node can deduce that it is still reachable. It is expected that the
mobile node will in most cases be able to determine its reachability mobile node will in most cases be able to determine its reachability
from the router by listening for packets from the router as described from the router by listening for packets from the router as described
above, and thus, such extra Neighbor Solicitation probes should above, and thus, such extra Neighbor Solicitation probes should
rarely be necessary. rarely be necessary.
With some types of networks, it is possible that additional With some types of networks, it is possible that additional
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node is reachable. For example, a mobile node MAY use signal node is reachable. For example, a mobile node MAY use signal
strength or signal quality information (with suitable hysteresis) for strength or signal quality information (with suitable hysteresis) for
its link with the available routers to decide when to switch to a new its link with the available routers to decide when to switch to a new
primary care-of address using that router rather than its current primary care-of address using that router rather than its current
default router (and current primary care-of address). Even though default router (and current primary care-of address). Even though
the mobile node's current default router may still be reachable in the mobile node's current default router may still be reachable in
terms of Neighbor Unreachability Detection, the mobile node MAY use terms of Neighbor Unreachability Detection, the mobile node MAY use
such lower-layer information to determine that switching to a new such lower-layer information to determine that switching to a new
default router would provide a better connection. default router would provide a better connection.
10.3. Forming New Care-of Addresses 10.4. Forming New Care-of Addresses
After detecting that it has moved from one link to another (i.e., its After detecting that it has moved from one link to another (i.e., its
current default router has become unreachable and it has discovered a current default router has become unreachable and it has discovered a
new default router), a mobile node SHOULD form a new primary care-of new default router), a mobile node SHOULD form a new primary care-of
address using one of the on-link subnet prefixes advertised by the address using one of the on-link subnet prefixes advertised by the
new router. A mobile node MAY form a new primary care-of address new router. A mobile node MAY form a new primary care-of address
at any time, except that it MUST NOT do so too frequently (not more at any time, except that it MUST NOT do so too frequently (not more
often than once per MAX_UPDATE_RATE seconds). often than once per MAX_UPDATE_RATE seconds).
In addition, after discovering a new on-link subnet prefix, a mobile In addition, after discovering a new on-link subnet prefix, a mobile
node MAY form a new (non-primary) care-of address using that subnet node MAY form a new (non-primary) care-of address using that subnet
prefix, even when it has not switched to a new default router. A prefix, even when it has not switched to a new default router. A
mobile node can have only one primary care-of address at a time mobile node can have only one primary care-of address at a time
(which is registered with its home agent), but it MAY have an (which is registered with its home agent), but it MAY have an
additional care-of address for any or all of the subnet prefixes on additional care-of address for any or all of the prefixes on its
its current link. Furthermore, since a wireless network interface current link. Furthermore, since a wireless network interface may
may actually allow a mobile node to be reachable on more than one actually allow a mobile node to be reachable on more than one link at
link at a time (i.e., within wireless transmitter range of routers a time (i.e., within wireless transmitter range of routers on more
on more than one separate link), a mobile node MAY have care-of than one separate link), a mobile node MAY have care-of addresses
addresses on more than one link at a time. The use of more than one on more than one link at a time. The use of more than one care-of
care-of address at a time is described in Section 10.12. address at a time is described in Section 10.15.
As described in Section 4, in order to form a new care-of address, As described in Section 4, in order to form a new care-of address,
a mobile node MAY use either stateless [18] or stateful (e.g., a mobile node MAY use either stateless [22] or stateful (e.g.,
DHCPv6 [2]) address autoconfiguration. If a mobile node needs to DHCPv6 [2]) address autoconfiguration. If a mobile node needs to
send packets as part of the method of address autoconfiguration, send packets as part of the method of address autoconfiguration,
it MUST use an IPv6 link-local address rather than its own IPv6 it MUST use an IPv6 link-local address rather than its own IPv6
home address as the Source Address in the IPv6 header of each such home address as the Source Address in the IPv6 header of each such
autoconfiguration packet. autoconfiguration packet.
In some cases, a mobile node may already know a (constant) IPv6 In some cases, a mobile node may already know a (constant) IPv6
address that has been assigned to it for its use only while address that has been assigned to it for its use only while
visiting a specific foreign link. For example, a mobile node may be visiting a specific foreign link. For example, a mobile node may be
statically configured with an IPv6 address assigned by the system statically configured with an IPv6 address assigned by the system
administrator of some foreign link, for its use while visiting that administrator of some foreign link, for its use while visiting that
link. If so, rather than using address autoconfiguration to form a link. If so, rather than using address autoconfiguration to form a
new care-of address using this subnet prefix, the mobile node MAY use new care-of address using this subnet prefix, the mobile node MAY use
its own pre-assigned address as its care-of address on this link. its own pre-assigned address as its care-of address on this link.
10.4. Sending Binding Updates to the Home Agent 10.5. Sending Binding Updates to the Home Agent
After deciding to change its primary care-of address as described After deciding to change its primary care-of address as described
in Sections 10.2 and 10.3, a mobile node MUST register this care-of in Sections 10.3 and 10.4, a mobile node MUST register this care-of
address with its home agent in order to make this its primary care-of address with its home agent in order to make this its primary care-of
address. To do so, the mobile node sends a packet to its home agent address. To do so, the mobile node sends a packet to its home agent
containing a Binding Update option, with the packet constructed as containing a Binding Update option, with the packet constructed as
follows: follows:
- The Home Registration (H) bit MUST be set in the Binding Update. - The Home Registration (H) bit MUST be set in the Binding Update.
- The Acknowledge (A) bit MUST be set in the Binding Update. - The Acknowledge (A) bit MUST be set in the Binding Update.
- The packet MUST contain a Home Address option, giving the mobile - The packet MUST contain a Home Address option, giving the mobile
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timeout period of MAX_BINDACK_TIMEOUT, the mobile node SHOULD timeout period of MAX_BINDACK_TIMEOUT, the mobile node SHOULD
continue to periodically retransmit the Binding Update at this rate continue to periodically retransmit the Binding Update at this rate
until acknowledged (or until it begins attempting to register a until acknowledged (or until it begins attempting to register a
different primary care-of address). different primary care-of address).
The Prefix Length field in the Binding Update allows the mobile node The Prefix Length field in the Binding Update allows the mobile node
to request its home agent to serve all home addresses for the mobile to request its home agent to serve all home addresses for the mobile
node, as indicated by the interface identifier in the mobile node's node, as indicated by the interface identifier in the mobile node's
home address (the remaining low-order bits after the indicated subnet home address (the remaining low-order bits after the indicated subnet
prefix), together with each on-link subnet prefix on the home link. prefix), together with each on-link subnet prefix on the home link.
Until the lifetime of this registration expires, the home agent
considers itself the home agent for each such home address of the
mobile node. As the set of on-link subnet prefixes on the home link
changes over time, the home agent changes the set of home addresses
for this mobile node for which it is serving as the home agent.
If the mobile node has additional home addresses using a different If the mobile node has additional home addresses using a different
interface identifier, then the mobile node SHOULD send an additional interface identifier, then the mobile node SHOULD send an additional
Binding Update to its home agent to register the care-of address for packet containing a Binding Update to its home agent to register
each such other home address (or set of home addresses sharing an the care-of address for each such other home address (or set of
interface identifier). home addresses sharing an interface identifier). These additional
Binding Updates MUST each be sent as a separate packet, since each
MUST contain an AH [8] or ESP [9] header to authenticate the Binding
Update as coming from the home address being bound.
It is possible that when the mobile node needs to send such a Binding 10.6. Dynamic Home Agent Address Discovery
Update to its home agent, that the mobile node does not know the
It is possible that when the mobile node needs to send a Binding
Update to its home agent to register its new primary care-of address,
as described in Section 10.5, the mobile node may not know the
address of any router on its home link that can serve as a home agent address of any router on its home link that can serve as a home agent
for it. In this case, the mobile node SHOULD use the dynamic home for it. For example, some nodes on its home link may have been
agent address discovery procedure to find the address of a suitable reconfigured while the mobile node has been away from home, such that
home agent on its home link. To do so, the mobile node sends the the router that was operating as the mobile node's home agent has
packet, as described above, with the Destination Address in the been replaced by a different router serving this role.
packet's IPv6 header set to the Home-Agents anycast address for its
home subnet prefix. As described in Section 9.2, the home agent In this case, the mobile node SHOULD use the dynamic home agent
on its home link that receives this Binding Update will reject the address discovery procedure to find the address of a suitable home
Update, returning to the mobile node the home agent's own unicast agent on its home link. To do so, the mobile node sends the packet,
IP address along with a list of the unicast IP addresses of each as described above, with the Destination Address in the packet's IPv6
other home agent operating on the home link. The mobile node SHOULD header set to the Home-Agents anycast address for its home subnet
then retransmit its Binding Update to one of these homes agent prefix. As described in Section 9.2, the home agent on its home link
using the provided unicast address; the mobile node MAY re-attempt that receives this Binding Update will reject the Update, returning
to the mobile node the home agent's own global unicast IP address
along with a list of the global unicast IP addresses of each other
home agent operating on the home link. The mobile node SHOULD then
retransmit its Binding Update to one of these homes agent using the
provided global unicast address; the mobile node MAY re-attempt
this home registration with each of these home agents in turn, by this home registration with each of these home agents in turn, by
sending each a Binding Update and waiting for the matching Binding sending each a Binding Update and waiting for the matching Binding
Acknowledgement, until its registration is accepted by one of these Acknowledgement, until its registration is accepted by one of these
home agents. home agents.
If the mobile node has a current registration with some home agent If the mobile node has a current registration with some home agent
on its home link (the Lifetime for that registration has not yet on its home link (the Lifetime for that registration has not yet
expired), then the mobile node MUST attempt any new registration expired), then the mobile node MUST attempt any new registration
first with that home agent. If that registration attempt fails first with that home agent. If that registration attempt fails
(e.g., times out or is rejected), the mobile node SHOULD then (e.g., times out or is rejected), the mobile node SHOULD then
reattempt this registration with another home agent on its home link. reattempt this registration with another home agent on its home link.
If the mobile node knows of no other suitable home agent, then it MAY If the mobile node knows of no other suitable home agent, then it MAY
attempt the dynamic home agent address discovery procedure described attempt the dynamic home agent address discovery procedure described
above. above.
10.5. Sending Binding Updates to Correspondent Nodes 10.7. Sending Binding Updates to Correspondent Nodes
A mobile node MAY send a Binding Update to any correspondent node at A mobile node MAY send a Binding Update to any correspondent node at
any time to allow it to cache its current care-of address (subject to any time to allow it to cache its current care-of address (subject to
the rate limiting defined in Section 10.8). In any Binding Update the rate limiting defined in Section 10.10). In any Binding Update
sent by a mobile node, the care-of address (either the Source Address sent by a mobile node, the care-of address (either the Source Address
in the packet's IPv6 header or the Care-of Address field in the in the packet's IPv6 header or the Care-of Address field in the
Binding Update) MUST be set to one of the care-of addresses currently Binding Update) MUST be set to one of the care-of addresses currently
in use by the mobile node or to the mobile node's home address. in use by the mobile node or to the mobile node's home address.
If set to one of the mobile node's current care-of addresses (the If set to one of the mobile node's current care-of addresses (the
care-of address given MAY differ from the mobile node's primary care-of address given MAY differ from the mobile node's primary
care-of address), the Binding Update requests the correspondent node care-of address), the Binding Update requests the correspondent node
to create or update an entry for the mobile node in the correspondent to create or update an entry for the mobile node in the correspondent
node's Binding Cache to record this care-of address for use in node's Binding Cache to record this care-of address for use in
sending future packets to the mobile node. If, instead, the care-of sending future packets to the mobile node. In this case, the
address is set to the mobile node's home address, the Binding Update Lifetime value sent in the Binding Update MUST be no greater than
requests the correspondent node to delete any existing Binding Cache the remaining lifetime of the mobile node's home registration of its
entry that it has for the mobile node. A mobile node MAY set the primary care-of address at its home agent.
care-of address differently for sending Binding Updates to different
correspondent nodes. If, instead, the care-of address is set to the mobile node's home
address, the Binding Update requests the correspondent node to delete
any existing Binding Cache entry that it has for the mobile node.
A mobile node MAY set the care-of address differently for sending
Binding Updates to different correspondent nodes.
When sending any Binding Update, the mobile node MUST record in its When sending any Binding Update, the mobile node MUST record in its
Binding Update List the following fields from the Binding Update: Binding Update List the following fields from the Binding Update:
- The IP address of the node to which the Binding Update was sent. - The IP address of the node to which the Binding Update was sent.
- The home address for which the Binding Update was sent, - The home address for which the Binding Update was sent.
- The remaining lifetime of the binding, initialized from the - The remaining lifetime of the binding, initialized from the
Lifetime field sent in the Binding Update. Lifetime field sent in the Binding Update.
The mobile node MUST retain in its Binding Update List information The mobile node MUST retain in its Binding Update List information
about all Binding Updates sent, for which the lifetime of the about all Binding Updates sent, for which the lifetime of the binding
binding has not yet expired. When sending a Binding Update, if an has not yet expired. However, when sending a Binding Update, if an
entry already exists in the mobile node's Binding Update List for entry already exists in the mobile node's Binding Update List for
an earlier Binding Update sent to that same destination node, the an earlier Binding Update sent to that same destination node, the
existing Binding Update List entry is updated to reflect the new existing Binding Update List entry is updated to reflect the new
Binding Update rather than creating a new Binding Update List entry. Binding Update rather than creating a new Binding Update List entry.
In general, when a mobile node sends a Binding Update to its home In general, when a mobile node sends a Binding Update to its home
agent to register a new primary care-of address (as described in agent to register a new primary care-of address (as described in
Section 10.4), the mobile node will also send a Binding Update to Section 10.5), the mobile node will also send a Binding Update to
each correspondent node for which an entry exists in the mobile each other node for which an entry exists in the mobile node's
node's Binding Update List. Thus, correspondent nodes are generally Binding Update List. Thus, other relevant nodes are generally kept
kept updated about the mobile node's binding and can send packets updated about the mobile node's binding and can send packets directly
directly to the mobile node using the mobile node's current care-of to the mobile node using the mobile node's current care-of address.
address.
The mobile node, however, need not send these Binding Updates The mobile node, however, need not send these Binding Updates
immediately after configuring a new care-of address. For example, immediately after configuring a new care-of address. For example,
since the Binding Update is a destination option and can be included since the Binding Update is a destination option and can be included
in any packet sent by a mobile node, the mobile node MAY delay in any packet sent by a mobile node, the mobile node MAY delay
sending a new Binding Update to any correspondent node for a sending a new Binding Update to any correspondent node for a
short period of time, in hopes that the needed Binding Update short period of time, in hopes that the needed Binding Update
can be included in some packet that the mobile node sends to that can be included in some packet that the mobile node sends to that
correspondent node for some other reason (for example, as part of correspondent node for some other reason (for example, as part of
some TCP connection in use). In this case, when sending a packet some TCP connection in use). In this case, when sending a packet
to some correspondent node, the mobile node SHOULD check in its to some correspondent node, the mobile node SHOULD check in its
Binding Update List to determine if a new Binding Update to this Binding Update List to determine if a new Binding Update to this
correspondent node is needed, and SHOULD include the new Binding correspondent node is needed, and SHOULD include the new Binding
Update in this packet as necessary. Update in this packet as necessary.
In addition, when a mobile node receives a packet for which the In addition, when a mobile node receives a packet for which the
mobile node can deduce that the original sender of the packet has no mobile node can deduce that the original sender of the packet has
Binding Cache entry for the mobile node, or for which the mobile node no Binding Cache entry for the mobile node, or for which the mobile
can deduce that the original sender of the packet has an out-of-date node can deduce that the original sender of the packet has an
care-of address for the mobile node in its Binding Cache, the mobile out-of-date care-of address for the mobile node in its Binding Cache,
node SHOULD return a Binding Update to the sender giving its current the mobile node SHOULD return a Binding Update to the sender giving
care-of address. In particular, the mobile node SHOULD return a its current care-of address (subject to the rate limiting defined
in Section 10.10). In particular, the mobile node SHOULD return a
Binding Update in response to receiving a packet that meets all of Binding Update in response to receiving a packet that meets all of
the following tests: the following tests:
- The packet was tunneled using IPv6 encapsulation. - The packet was tunneled using IPv6 encapsulation.
- The Destination Address in the tunnel (outer) IPv6 header is - The Destination Address in the tunnel (outer) IPv6 header is
equal to any of the mobile node's care-of addresses. equal to any of the mobile node's care-of addresses.
- The Destination Address in the original (inner) IPv6 header is - The Destination Address in the original (inner) IPv6 header
equal to the mobile node's home address. If the original packet is equal to one of the mobile node's home addresses; or this
contains a Routing header, the final Address indicated in the Destination Address is equal to one of the mobile node's previous
Routing header should be used in this comparison rather than the care-of addresses, if the mobile node has an entry in its Binding
Destination Address in the original IPv6 header. Update List representing an unexpired Binding Update sent to
a previous default router for this previous care-of address
(Section 10.8).
- The Source Address in the tunnel (outer) IPv6 header differs from - The Source Address in the tunnel (outer) IPv6 header differs from
the Source Address in the original (inner) IPv6 header. the Source Address in the original (inner) IPv6 header.
The destination address to which the Binding Update should be sent in The destination address to which the Binding Update should be sent
response to receiving a packet meeting all of the tests above, is the in response to receiving a packet meeting all of the above tests is
Source Address in the original (inner) IPv6 header of the packet. the Source Address in the original (inner) IPv6 header of the packet.
The home address for which this Binding Update is sent should be the
Destination Address of the original (inner) packet.
Binding Updates sent to correspondent nodes are not generally Binding Updates sent to correspondent nodes are not generally
required to be acknowledged. However, if the mobile node wants to be required to be acknowledged. However, if the mobile node wants
sure that its new care-of address has been added to a correspondent to be sure that its new care-of address has been entered into a
node's Binding Cache, the mobile node MAY request an acknowledgement correspondent node's Binding Cache, the mobile node MAY request an
by setting the Acknowledge (A) bit in the Binding Update. In this acknowledgement by setting the Acknowledge (A) bit in the Binding
case, however, the mobile node SHOULD NOT continue to retransmit the Update. In this case, however, the mobile node SHOULD NOT continue
Binding Update once the retransmission timeout period has reached to retransmit the Binding Update once the retransmission timeout
MAX_BINDACK_TIMEOUT. period has reached MAX_BINDACK_TIMEOUT.
A mobile node MAY choose to keep its location private from certain A mobile node MAY choose to keep its location private from certain
correspondent nodes, and thus need not send new Binding Updates to correspondent nodes, and thus need not send new Binding Updates to
those correspondents. A mobile node MAY also send a Binding Update those correspondents. A mobile node MAY also send a Binding Update
to such a correspondent node to instruct it to delete any existing to such a correspondent node to instruct it to delete any existing
binding for the mobile node from its Binding Cache, as described in binding for the mobile node from its Binding Cache, as described in
Section 5.1. No other IPv6 nodes are authorized to send Binding Section 5.1. No other IPv6 nodes are authorized to send Binding
Updates on behalf of a mobile node. Updates on behalf of a mobile node.
10.6. Sending Binding Updates to the Previous Default Router 10.8. Sending Binding Updates to the Previous Default Router
After switching to a new default router (and thus also changing its After switching to a new default router (and thus also changing its
primary care-of address), a mobile node MAY send a Binding Update primary care-of address), a mobile node MAY send a Binding Update to
to its previous default router, giving its new care-of address. its previous default router, giving its new care-of address. The
packet carrying the Binding Update MUST be addressed to the mobile
node's previous default router's global unicast address, learned
by the mobile node based on Prefix Information options received in
Router Advertisements from it in which the Router Address (R) bit is
set.
If the mobile node sends such a Binding Update, the home address If the mobile node sends such a Binding Update, the home address
for the binding, specified in the Home Address option included in for the binding, specified in the Home Address option included in
the packet carrying this Binding Update, MUST be set the mobile the packet carrying this Binding Update, MUST be set the mobile
node's old primary care-of address (that it used while using this node's old primary care-of address (that it used while using this
default router), and the care-of address for the binding (either the default router), and the care-of address for the binding (either the
Source Address in the packet's IPv6 header or the Care-of Address Source Address in the packet's IPv6 header or the Care-of Address
field in the Binding Update) MUST be set to the mobile node's new field in the Binding Update) MUST be set to the mobile node's new
primary care-of address. In addition, the Home Registration (H) primary care-of address. In addition, the Home Registration (H)
bit MUST also be set in this Binding Update, to request the mobile bit MUST also be set in this Binding Update, to request the mobile
node's previous default router to temporarily act as a home agent node's previous default router to temporarily act as a home agent
for the mobile node's old primary care-of address. The previous for the mobile node's old primary care-of address. The previous
default router will thus tunnel packets for the mobile node to its default router will thus tunnel packets for the mobile node to its
new care-of address. All of the procedures defined for home agent new care-of address. All of the procedures defined for home agent
operation must be followed by this previous default router for this operation must be followed by this previous default router for this
registration. Note that the previous router does not necessarily registration. Note that the previous router does not necessarily
know the mobile node's (permanent) home address as part of this know the mobile node's (permanent) home address as part of this
registration. registration.
10.7. Retransmitting Binding Updates 10.9. Retransmitting Binding Updates
If, after sending a Binding Update in which the Acknowledge (A) bit If, after sending a Binding Update in which the Acknowledge (A) bit
is set, a mobile node fails to receive a Binding Acknowledgement is set, a mobile node fails to receive a Binding Acknowledgement
within INITIAL_BINDACK_TIMEOUT seconds, the mobile node SHOULD within INITIAL_BINDACK_TIMEOUT seconds, the mobile node SHOULD
retransmit the Binding Update until a Binding Acknowledgement retransmit the Binding Update until a Binding Acknowledgement
is received. Such a retransmitted Binding Update MUST use he is received. Such a retransmitted Binding Update MUST use the
same Sequence Number value as the original transmission. The same Sequence Number value as the original transmission. The
retransmissions by the mobile node MUST use an exponential retransmissions by the mobile node MUST use an exponential
back-off process, in which the timeout period is doubled back-off process, in which the timeout period is doubled
upon each retransmission until either the node receives a upon each retransmission until either the node receives a
Binding Acknowledgement or the timeout period reaches the value Binding Acknowledgement or the timeout period reaches the value
MAX_BINDACK_TIMEOUT. MAX_BINDACK_TIMEOUT.
10.8. Rate Limiting for Sending Binding Updates 10.10. Rate Limiting for Sending Binding Updates
A mobile node MUST NOT send Binding Updates more often than once per A mobile node MUST NOT send Binding Updates more often than once per
MAX_UPDATE_RATE seconds to any node. After sending MAX_FAST_UPDATES MAX_UPDATE_RATE seconds to any node. After sending MAX_FAST_UPDATES
consecutive Binding Updates to a particular node with the same consecutive Binding Updates to a particular node with the same
care-of address, the mobile node SHOULD reduce its rate of sending care-of address, the mobile node SHOULD reduce its rate of sending
Binding Updates to that node, to the rate of SLOW_UPDATE_RATE per Binding Updates to that node, to the rate of SLOW_UPDATE_RATE per
second. The mobile node MAY continue to send Binding Updates at the second. The mobile node MAY continue to send Binding Updates at this
slower rate indefinitely, in hopes that the node will eventually slower rate indefinitely, in hopes that the node will eventually
be able to process a Binding Update and begin to route its packets be able to process a Binding Update and begin to route its packets
directly to the mobile node at its new care-of address. directly to the mobile node at its new care-of address.
10.9. Receiving ICMP Error Messages 10.11. Receiving Binding Acknowledgements
The Option Type value for a Binding Update option specifies that
any node receiving this option that does not recognize the Option
Type SHOULD return an ICMP Parameter Problem, Code 2, message to
the sender of the packet containing the Binding Update option. If
a node sending a Binding Update receives such an ICMP error message
in response, it should record in its Binding Update List that future
Binding Updates should not be sent to this destination.
Likewise, although ALL IPv6 nodes (whether host or router, whether
mobile or stationary) MUST implement the ability to receive packets
containing a Home Address option, all Option Type values in IPv6
include a specification of the behavior that a node receiving a
packet containing this option performs if it does not implement
receipt of that type of option. For the Home Address option, the
Option Type value specifies that any node receiving this option that
does not recognize the Option Type SHOULD return an ICMP Parameter
Problem, Code 2, message to the sender of the packet containing the
Home Address option. If a mobile node receives such an ICMP error
message from some node indicating that it does not recognize the
mobile node's Home Address option, the mobile node SHOULD log the
error and then discard the ICMP message; this error message indicates
that the node to which the original packet was addressed (the node
returning the ICMP error message) does not correctly implement this
required part of the IPv6 protocol.
10.10. Receiving Binding Acknowledgements
Upon receiving a packet carrying a Binding Acknowledgement, a mobile Upon receiving a packet carrying a Binding Acknowledgement, a mobile
node MUST validate the packet according to the following tests: node MUST validate the packet according to the following tests:
- The packet contains either an AH [7] or ESP [8] header providing - The packet contains a valid AH [8] or ESP [9] header providing
sender authentication, data integrity protection, and replay sender authentication, data integrity protection, and replay
protection. protection.
- The Option Length field in the option is greater than or equal to - The Option Length field in the option is greater than or equal to
11 octets. 11 octets.
- The Sequence Number field matches the Sequence Number sent by the - The Sequence Number field matches the Sequence Number sent by the
mobile node to this destination address in an outstanding Binding mobile node to this destination address in an outstanding Binding
Update. Update.
skipping to change at page 57, line 34 skipping to change at page 73, line 13
according to any procedure defined for that part of the packet. according to any procedure defined for that part of the packet.
When a mobile node receives a packet carrying a valid Binding When a mobile node receives a packet carrying a valid Binding
Acknowledgement, the mobile node MUST examine the Status field as Acknowledgement, the mobile node MUST examine the Status field as
follows: follows:
- If the Status field indicates that the Binding Update was - If the Status field indicates that the Binding Update was
accepted (the Status field is less than 128), then the mobile accepted (the Status field is less than 128), then the mobile
node MUST update the corresponding entry in its Binding Update node MUST update the corresponding entry in its Binding Update
List to indicate that the Binding Update has been acknowledged. List to indicate that the Binding Update has been acknowledged.
The mobile node MUST thus stop retransmitting the Binding Update. The mobile node MUST then stop retransmitting the Binding Update.
- If the Status field indicates that the Binding Update was - If the Status field indicates that the Binding Update was
rejected (the Status field is greater than or equal to 128), then rejected (the Status field is greater than or equal to 128), then
the mobile node MUST delete the corresponding Binding Update List the mobile node MUST delete the corresponding Binding Update List
entry (and MUST also stop retransmitting the Binding Update). entry (and MUST also stop retransmitting the Binding Update).
Optionally, the mobile node MAY then take steps to correct the Optionally, the mobile node MAY then take steps to correct the
cause of the error and retransmit the Binding Update (with a new cause of the error and retransmit the Binding Update (with a new
Sequence Number value), subject to the rate limiting restriction Sequence Number value), subject to the rate limiting restriction
specified in Section 10.8. In particular, if the Status field specified in Section 10.10. In particular, if the Status field
is equal to 135 (dynamic home agent address discovery response), is equal to 135 (dynamic home agent address discovery response),
then the mobile node MAY reattempt its home registration with any then the mobile node MAY reattempt its home registration with
of the home agent IP addresses listed in the Other Home Agents the home agent address given in the Source Address field of the
field in the Binding Acknowledgement or with the home agent packet carrying the Binding Acknowledgement or with any of the
address given in the Source Address field of the packet carrying home agent IP addresses listed in the Home Agents List field in
the Binding Acknowledgement. If any of these addresses is not the Binding Acknowledgement. If any of these addresses is not a
unicast a address or does not have a subnet prefix equal to the global unicast address or does not have a subnet prefix equal to
mobile node's own subnet prefix, then that particular address the mobile node's own subnet prefix, then that particular address
MUST be ignored and the mobile node MUST NOT reattempt its home MUST be ignored and the mobile node MUST NOT reattempt its home
registration with that home agent. registration with that home agent.
10.11. Receiving Binding Requests 10.12. Receiving Binding Requests
When a mobile node receives a packet containing a Binding Request, When a mobile node receives a packet containing a Binding Request,
it SHOULD return to the sender a packet containing a Binding Update. it SHOULD return to the sender a packet containing a Binding Update.
The Lifetime field in this Binding Update SHOULD be set to a new The Lifetime field in this Binding Update SHOULD be set to a new
lifetime, extending any current lifetime remaining from a previous lifetime, extending any current lifetime remaining from a previous
Binding Update sent to this node (as indicated in any existing Binding Update sent to this node (as indicated in any existing
Binding Update List entry for this node). When sending this Binding Binding Update List entry for this node), except that this lifetime
Update, the mobile node MUST update its Binding Update List in the MUST NOT exceed the remaining lifetime for the mobile node's primary
same way as for any other Binding Update sent by the mobile node. care-of address registration at its home agent. When sending this
Binding Update, the mobile node MUST update its Binding Update List
in the same way as for any other Binding Update sent by the mobile
node.
Note, however, that the mobile node MAY choose to keep its current Note, however, that the mobile node MAY choose to keep its current
binding private from the sender of the Binding Request. In this binding private from the sender of the Binding Request. In this
case, the mobile node instead SHOULD returns a Binding Update to the case, the mobile node instead SHOULD returns a Binding Update to the
sender, in which the Lifetime field is set to zero. sender, in which the Lifetime field is set to zero and the care-of
address is set to the mobile node's home address.
10.12. Using Multiple Care-of Addresses 10.13. Receiving ICMP Error Messages
As described in Section 10.3, a mobile node MAY use more than one The Option Type value for a Binding Update option specifies that
any node receiving this option that does not recognize the Option
Type SHOULD return an ICMP Parameter Problem, Code 2, message to
the sender of the packet containing the Binding Update option. If
a node sending a Binding Update receives such an ICMP error message
in response, it should record in its Binding Update List that future
Binding Updates should not be sent to this destination.
Likewise, although ALL IPv6 nodes (whether host or router, whether
mobile or stationary) MUST implement the ability to correctly process
received packets containing a Home Address option, all Option Type
values in IPv6 include a specification of the behavior that a node
receiving a packet containing this option performs if it does not
implement receipt of that type of option. For the Home Address
option, the Option Type value specifies that any node receiving
this option that does not recognize the Option Type SHOULD return
an ICMP Parameter Problem, Code 2, message to the sender of the
packet containing the Home Address option. If a mobile node receives
such an ICMP error message from some node indicating that it does
not recognize the mobile node's Home Address option, the mobile
node SHOULD log the error and then discard the ICMP message; this
error message indicates that the node to which the original packet
was addressed (the node returning the ICMP error message) does not
correctly implement this required part of the IPv6 protocol.
10.14. Receiving Tunneled Router Advertisements
Section 9.7 describes the operation of a home agent to support
renumbering a mobile node's home subnet while the mobile node is
away from home. The home agent tunnels certain Router Advertisement
messages to the mobile node while away from home, giving "important"
Prefix Information options that describe changes in the prefixes in
use on the mobile node's home link.
When a mobile node receives a tunneled Router Advertisement, it MUST
validate it according to the following tests:
- The Source Address of the IP packet carrying the Router
Advertisement is the same as the home agent address to which the
mobile node last sent an accepted "home registration" Binding
Update to register its primary care-of address.
- The packet contains either an AH [8] or ESP [9] header providing
sender authentication, data integrity protection, and replay
protection.
- The packet contains a Binding Request destination option.
Any received tunneled Router Advertisement not meeting all of these
tests MUST be silently discarded.
If a received tunneled Router Advertisement is not discarded
according to the tests listed above, the mobile node MUST process the
Router Advertisement as if it were connected to its home link [13].
Such processing MAY result in the mobile node configuring a new home
address, although due to separation between preferred lifetime and
valid lifetime, such changes should not affect most communication by
the mobile node, in the same way as for nodes that are at home.
In addition, in processing the packet containing this Router
Advertisement, the mobile node SHOULD return to the home agent a
Binding Update in response to the Binding Request carried in the
packet. The correct formation of this Binding Update by the mobile
node and processing of it by the home agent will be viewed by the
home agent as an acknowledgement of this Router Advertisement,
confirming to it that this Router Advertisement was received by the
mobile node.
10.15. Using Multiple Care-of Addresses
As described in Section 10.4, a mobile node MAY use more than one
care-of address at a time. Particularly in the case of many wireless care-of address at a time. Particularly in the case of many wireless
networks, a mobile node effectively might be reachable through networks, a mobile node effectively might be reachable through
multiple links at the same time (e.g., with overlapping wireless multiple links at the same time (e.g., with overlapping wireless
cells), on which different on-link subnet prefixes may exist. A cells), on which different on-link subnet prefixes may exist. A
mobile node SHOULD select a primary care-of address from among those mobile node SHOULD select a primary care-of address from among those
care-of addresses it has formed using any of these subnet prefixes, care-of addresses it has formed using any of these subnet prefixes,
based on the movement detection mechanism in use, as described in based on the movement detection mechanism in use, as described in
Section 10.2. When the mobile node selects a new primary care-of Section 10.3. When the mobile node selects a new primary care-of
address, it MUST register it with its home agent through a Binding address, it MUST register it with its home agent by sending it a
Update with the Home Registration (H) and Acknowledge (A) bits set, Binding Update with the Home Registration (H) and Acknowledge (A)
as described in Section 10.4. bits set, as described in Section 10.5.
To assist with smooth handoffs, a mobile node SHOULD retain To assist with smooth handoffs, a mobile node SHOULD retain
its previous primary care-of address as a (non-primary) care-of its previous primary care-of address as a (non-primary) care-of
address, and SHOULD still accept packets at this address, even after address, and SHOULD still accept packets at this address, even after
registering its new primary care-of address with its home agent. registering its new primary care-of address with its home agent.
This is reasonable, since the mobile node could only receive packets This is reasonable, since the mobile node could only receive packets
at its previous primary care-of address if it were indeed still at its previous primary care-of address if it were indeed still
connected to that link. If the previous primary care-of address was connected to that link. If the previous primary care-of address was
allocated using stateful address autoconfiguration [2], the mobile allocated using stateful address autoconfiguration [2], the mobile
node may not wish to release the address immediately upon switching node may not wish to release the address immediately upon switching
to a new primary care-of address. to a new primary care-of address.
10.13. Routing Multicast Packets 10.16. Routing Multicast Packets
A mobile node that is connected to its home link functions in the A mobile node that is connected to its home link functions in the
same way as any other (stationary) node. Thus, when it is at home, same way as any other (stationary) node. Thus, when it is at home,
a mobile node functions identically to other multicast senders and a mobile node functions identically to other multicast senders and
receivers. This section therefore describes the behavior of a mobile receivers. This section therefore describes the behavior of a mobile
node that is not on its home link. node that is not on its home link.
In order to receive packets sent to some multicast group, a mobile In order to receive packets sent to some multicast group, a mobile
node must join that multicast group. One method by which a mobile node must join that multicast group. One method by which a mobile
node MAY join the group is via a (local) multicast router on the node MAY join the group is via a (local) multicast router on the
foreign link being visited. The mobile node SHOULD use its care-of foreign link being visited. The mobile node SHOULD use its care-of
address sharing a subnet prefix with the multicast router, as address sharing a subnet prefix with the multicast router, as
the source IPv6 address of its multicast group membership control the source IPv6 address of its multicast group membership control
messages. messages.
Alternatively, a mobile node MAY join multicast groups via a Alternatively, a mobile node MAY join multicast groups via a
bi-directional tunnel to its home agent. The mobile node tunnels the bi-directional tunnel to its home agent. The mobile node tunnels its
appropriate multicast group membership control packets to its home multicast group membership control packets to its home agent, and the
agent, and the home agent forwards multicast packets down the tunnel home agent forwards multicast packets down the tunnel to the mobile
to the mobile node. node.
A mobile node that wishes to send packets to a multicast group A mobile node that wishes to send packets to a multicast group
also has two options: (1) send directly on the foreign link being also has two options: (1) send directly on the foreign link being
visited; or (2) send via a tunnel to its home agent. Because visited; or (2) send via a tunnel to its home agent. Because
multicast routing in general depends upon the Source Address used in multicast routing in general depends upon the Source Address used in
the IPv6 header of the multicast packet, a mobile node that tunnels a the IPv6 header of the multicast packet, a mobile node that tunnels a
multicast packet to its home agent MUST use its home address as the multicast packet to its home agent MUST use its home address as the
IPv6 Source Address of the inner multicast packet. IPv6 Source Address of the inner multicast packet.
10.14. Returning Home 10.17. Returning Home
A mobile node detects that it has returned to its home link through A mobile node detects that it has returned to its home link through
the movement detection algorithm in use (Section 10.2), when the the movement detection algorithm in use (Section 10.3), when the
mobile node detects that its home subnet prefix is again on-link. mobile node detects that its home subnet prefix is again on-link.
The mobile node SHOULD then send a Binding Update to its home agent, The mobile node SHOULD then send a Binding Update to its home agent,
to instruct its home agent to no longer intercept or tunnel packets to instruct its home agent to no longer intercept or tunnel packets
for it. In this Binding Update, the mobile node MUST set the care-of for it. In this Binding Update, the mobile node MUST set the care-of
address for the binding (the Source Address field in the packet's address for the binding (the Source Address field in the packet's
IPv6 header) to the mobile node's own home address. As with other IPv6 header) to the mobile node's own home address. As with other
Binding Updates sent to register with its home agent, the mobile Binding Updates sent to register with its home agent, the mobile
node MUST set the Acknowledge (A) and Home Registration (H) bits, node MUST set the Acknowledge (A) and Home Registration (H) bits,
and SHOULD retransmit the Binding Update until a matching Binding and SHOULD retransmit the Binding Update until a matching Binding
Acknowledgement is received. Acknowledgement is received.
In addition, the mobile node MUST multicast onto the home link In addition, the mobile node MUST multicast onto the home link
(to the all-nodes multicast address) a Neighbor Advertisement (to the all-nodes multicast address) a Neighbor Advertisement
message [11], to advertise the mobile node's own link-layer address message [13], to advertise the mobile node's own link-layer address
for its own home address. The Target Address in this Neighbor for its own home address. The Target Address in this Neighbor
Advertisement message MUST be set to the mobile node's home address, Advertisement message MUST be set to the mobile node's home address,
and the Advertisement MUST include a Target Link-layer Address option and the Advertisement MUST include a Target Link-layer Address option
specifying the mobile node's link-layer address. The mobile node specifying the mobile node's link-layer address. The mobile node
MUST multicast such a Neighbor Advertisement message for each of its MUST multicast such a Neighbor Advertisement message for each of its
home addresses, as defined by the current on-link prefixes, including home addresses, as defined by the current on-link prefixes, including
its link-local address and site-local address. The Solicited its link-local address and site-local address. The Solicited
Flag (S) in these Advertisements MUST NOT be set, since they were Flag (S) in these Advertisements MUST NOT be set, since they were
not solicited by any Neighbor Solicitation message. The Override not solicited by any Neighbor Solicitation message. The Override
Flag (O) in these Advertisements MUST be set, indicating that the Flag (O) in these Advertisements MUST be set, indicating that the
Advertisements SHOULD override any existing Neighbor Cache entries at Advertisements SHOULD override any existing Neighbor Cache entries at
any node receiving them. any node receiving them.
Since multicasts on the local link (such as Ethernet) are typically Since multicasts on the local link (such as Ethernet) are typically
not guaranteed to be reliable, the mobile node MAY retransmit these not guaranteed to be reliable, the mobile node MAY retransmit these
Neighbor Advertisement messages up to MAX_ADVERT_REXMIT times to Neighbor Advertisement messages up to MAX_ADVERT_REXMIT times to
increase their reliability. It is still possible that some nodes on increase their reliability. It is still possible that some nodes on
the home link will not receive any of these Neighbor Advertisements, the home link will not receive any of these Neighbor Advertisements,
but these nodes will eventually be able to recover through use of but these nodes will eventually be able to recover through use of
Neighbor Unreachability Detection [11]. Neighbor Unreachability Detection [13].
11. Constants 11. Constants
INITIAL_BINDACK_TIMEOUT 1 second INITIAL_BINDACK_TIMEOUT 1 second
MAX_BINDACK_TIMEOUT 256 seconds MAX_BINDACK_TIMEOUT 256 seconds
MAX_UPDATE_RATE once per second MAX_UPDATE_RATE once per second
SLOW_UPDATE_RATE once per 10 seconds SLOW_UPDATE_RATE once per 10 seconds
MAX_FAST_UPDATES 5 MAX_FAST_UPDATES 5 transmissions
MAX_ADVERT_REXMIT 3 MAX_ADVERT_REXMIT 3 transmissions
12. IANA Considerations 12. IANA Considerations
This document defines four new types of IPv6 destination options, This document defines four new types of IPv6 destination options,
each of which must be assigned an Option Type value: each of which must be assigned an Option Type value:
- The Binding Update option, described in Section 5.1 - The Binding Update option, described in Section 5.1
- The Binding Acknowledgement option, described in Section 5.2 - The Binding Acknowledgement option, described in Section 5.2
- The binding Request option, described in Section 5.3 - The binding Request option, described in Section 5.3
- The Home Address option, described in Section 5.4 - The Home Address option, described in Section 5.4
In addition, this document defines a new Neighbor Discovery [11] In addition, this document defines two new Neighbor Discovery [13]
option, which must be assigned an Option Type value within the option options, which must be assigned Option Type values within the option
numbering space for Neighbor Discovery messages: numbering space for Neighbor Discovery messages:
- The Advertisement Interval option, described in Section 6.2. - The Advertisement Interval option, described in Section 6.3.
- The Home Agent Information option, described in Section 6.4.
Finally, this document defines a new type of anycast address, which Finally, this document defines a new type of anycast address, which
must be assigned a reserved interface identifier value for use with must be assigned a reserved value for use with any subnet prefix to
any subnet prefix to define this anycast address on each subnet: define this anycast address on each subnet:
- The Home-Agents anycast address, used in the dynamic home agent - The Home-Agents anycast address, used in the dynamic home agent
address discovery procedure described in Sections 9.2 and 10.4. address discovery procedure described in Sections 9.2 and 10.6.
13. Security Considerations 13. Security Considerations
13.1. Binding Updates, Acknowledgements, and Requests 13.1. Binding Updates, Acknowledgements, and Requests
The Binding Update option described in this document will result The Binding Update option described in this document will result
in packets addressed to a mobile node being delivered instead to in packets addressed to a mobile node being delivered instead to
its care-of address. This ability to change the routing of these its care-of address. This ability to change the routing of these
packets could be a significant vulnerability if any packet containing packets could be a significant vulnerability if any packet containing
a Binding Update option was not authenticated. Such use of "remote a Binding Update option was not authenticated. Such use of "remote
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Although appropriate for many forms of communication, Binding Updates Although appropriate for many forms of communication, Binding Updates
MUST be applied only in the order sent. The Binding Update option MUST be applied only in the order sent. The Binding Update option
thus includes a Sequence Number field to provide this necessary thus includes a Sequence Number field to provide this necessary
sequencing. The use of this Sequence Number together with IPsec sequencing. The use of this Sequence Number together with IPsec
replay protection is similar in many ways, for example, to the the replay protection is similar in many ways, for example, to the the
sequence number in TCP. IPsec provides strong replay protection but sequence number in TCP. IPsec provides strong replay protection but
no ordering, and the sequence number provides ordering but need not no ordering, and the sequence number provides ordering but need not
worry about replay protection such as through the sequence number worry about replay protection such as through the sequence number
wrapping around. wrapping around.
13.2. Home Address Options 13.2. Home Address Option
No special authentication of the Home Address option is required, No special authentication of the Home Address option is required,
except that if the IPv6 header of a packet is covered by except that if the IPv6 header of a packet is covered by
authentication, then that authentication MUST also cover the Home authentication, then that authentication MUST also cover the Home
Address option; this coverage is achieved automatically by the Address option; this coverage is achieved automatically by the
definition of the Option Type code for the Home Address option definition of the Option Type code for the Home Address option
(Section 5.4), since it indicates that the option is included in the (Section 5.4), since it indicates that the option is included in the
authentication computation. Thus, even when authentication is used authentication computation. Thus, even when authentication is used
in the IPv6 header, the security of the Source Address field in the in the IPv6 header, the security of the Source Address field in the
IPv6 header is not compromised by the presence of a Home Address IPv6 header is not compromised by the presence of a Home Address
skipping to change at page 66, line 9 skipping to change at page 83, line 9
privacy is desired, the mobile node can create a tunnel to its home privacy is desired, the mobile node can create a tunnel to its home
agent. Then, packets destined for correspondent nodes will appear agent. Then, packets destined for correspondent nodes will appear
to emanate from the home subnet, and it may be more difficult to to emanate from the home subnet, and it may be more difficult to
pinpoint the location of the mobile node. Such mechanisms are all pinpoint the location of the mobile node. Such mechanisms are all
beyond the scope of this document. beyond the scope of this document.
Changes from Previous Draft Changes from Previous Draft
This appendix briefly lists some of the major changes in this This appendix briefly lists some of the major changes in this
draft relative to the previous version of this same draft, draft relative to the previous version of this same draft,
draft-ietf-mobileip-ipv6-04.txt: draft-ietf-mobileip-ipv6-05.txt:
- Replaced the ID Length field in the Binding Update with the
Prefix Length field.
- Added a definition of "interface identifier" in Section 3.1.
- Added a description of dynamic home agent address discovery to
the basic operation overview in Section 4.1.
- Added a description of the new Home Agents List conceptual data
structure in Section 4.3. This list is used in the dynamic home
agent address discovery mechanism.
- Added the Other Home Agents field to the Binding Acknowledgement
option format, and modified the description of the setting
for the Option Length field in the Binding Acknowledgement to
accommodate the Other Home Agents field. This field is used in
the dynamic home agent address discovery mechanism.
- Added Section 9.1, describing the processing performed by a - Clarified that the Advertisement Interval option in Section 6.3
home agent to maintain its Home Agents List when the home agent MAY be included in Router Advertisements by any router, not just
receives a valid Router Advertisement message in which the Home by home agents.
Agent (H) bit is set.
- Revised the description of dynamic home agent address discovery - Modified Section 6.5 to document a required change to the
in Section 9.2 to include use of the new Home Agents List and MaxRtrAdvInterval limit, in addition to the change to the
the return of the IP addresses from this list in the Other Home MinRtrAdvInterval limit, and clarified that these new limits MAY
Agents field of the Binding Acknowledgement that rejects the be used by any router, not just by home agents.
anycast Binding Update.
- Revised Section 10.10 to include a description of the Other Home - Added Section 6.6 to document new limits on sending Router
Agents field in the received Binding Acknowledgement. Solicitations by a mobile node while away from home. These
changes are related to the MAX_RTR_SOLICITATIONS and
RTR_SOLICITATION_INTERVAL Neighbor Discovery constants.
- Added Section 6, listing modifications to IPv6 Neighbor - Added Section 6.2 documenting a modification to the format of
Discovery: The Router Advertisement message is changed to a Prefix Information option for use in Router Advertisement
include the Home Agent (H) bit, a new Advertisement Interval messages. This modification allows a router to easily and
option is defined for Router Advertisement messages, and the efficiently advertise its own global unicast address.
value of MinRtrAdvInterval for home agents is allowed to be less
than the generic limit for routers of 3 seconds [11].
- Added a description in the IANA Considerations in Section 12, of - Defined a new Home Agent Information Option for Router
the need to assign an Option Type value for the new Advertisement Advertisements (Section 6.4). This option allows those routers
Interval option that can appear on Router Advertisement messages. functioning as a home agent to optionally specify a preference
(relative to other home agents on this link) and a lifetime for
this advertisement for providing home agent service. Use of this
option by home agents is optional.
- Changed the rule in Section 9.3 dealing with forwarding - Added Section 10.2, defining the general procedures to be used
site-local-addressed packets to a mobile node while the mobile by a mobile node in receiving packets while away from home. In
nodes is away from home. Such packets now MUST NOT be tunneled particular, for packets received with a Routing header, this
to the mobile node, unless the mobile node's registered primary section defines an exception for any use of a Routing header
care-of address is within the same site as the mobile node's home automatically derived by "reversing" the received Routing header,
address. for any response packets sent by upper-layer protocols.
- Added a description in Section 10.9 of what a mobile node should - Changed the treatment of packets addressed to a mobile node's
do if it receives an ICMP Parameter Problem error message in site-local address while the mobile node is away from home. The
response to the Home Address option in some packet that it current consensus of the Mobile IP Working Group is that such
sent. Although ALL IPv6 nodes MUST implement receipt of packets packets SHOULD be tunneled to the mobile node by default, but
containing a Home Address option, the encoding of an Option Type this behavior MUST be configurable to disable it; currently,
value in IPv6 always specifies some behavior for the case in the exact definition and semantics of a "site" and a site-local
which the receiver does not recognize that type of option. address are undefined in IPv6, and this default behavior might
change at some point in the future.
- In Section 10.2, changed SHOULD to MAY in specifying that upon - Added a definition of the treatment of multicast packets
lower-layer indication of link-layer mobility, the mobile node addressed to a multicast group to which a mobile node is
MAY send Router Solicitation messages to determine if new routers subscribed, for which the multicast scope is link-local,
are present on its new link. site-local, organization-local, etc. As with packets sent to a
mobile node's link-local and site-local addresses, link-local
multicast packets MUST NOT be tunneled to the mobile node, and
multicast packets addressed to a multicast address with scope
larger than link-local but smaller than global (e.g., site-local
and organization-local) SHOULD be tunneled to the mobile node by
default, but this behavior MUST be configurable to disable it.
- Also in Section 10.2, added a description of how the value - Added Section 7.2, detailing Mobile IP requirements on all IPv6
specified in the Advertisement Interval option in received routers. They SHOULD be able to send an Advertisement Interval
Router Advertisements MAY be used in the mobile node's movement option in their Router Advertisements, and SHOULD be able to
detection algorithm. support sending unsolicited multicast Router Advertisements at
the faster rate described in Section 6.5.
- Moved the section on routing multicast packets to and from a - Added Section 10.14 describing the mobile node side of
mobile host while away from home, to now be Section 10.13, renumbering the home network, matching the home agent processing
a subsection of the description of mobile node operation described in Section 9.7.
(Section 10), rather than being a separate section on its own.
This better integrates this operation into the document.
- Corrected the specification of the length of the Binding Update - Simplified the sequence of tests in Section 9.4 performed by a
option. The correct length is 24, not 16, if the Care-of Address home agent being requested to no longer serve as the sending
Present (C) bit is set. mobile node's home agent.
- Corrected the specification of the length of the Binding - Clarified in Section 10.5 that if a mobile node has multiple home
Acknowledgement option. The correct length is 11, not 12 (plus addresses using different interface identifiers, then it SHOULD
16 times the number of addresses listed in the Other Home Agents send a separate Binding Update to its home agent for each.
field in the Acknowledgement).
- Other minor clarifications and correction of typographical errors - Finally filled in Section 2, giving a comparison of Mobile IPv6
throughout. with Mobile IP for IPv4.
Acknowledgements Acknowledgements
We would like to thank the members of the Mobile IP and IPng Working We would like to thank the members of the Mobile IP and IPng Working
Groups for their comments and suggestions on this work. We would Groups for their comments and suggestions on this work. We would
particularly like to thank Josh Broch, Thomas Narten, Erik Nordmark, particularly like to thank Josh Broch, Thomas Narten, Erik Nordmark,
and Jim Solomon for their detailed reviews of earlier versions of and Jim Solomon for their detailed reviews of earlier versions of
this draft. Their suggestions have helped to improve both the design this draft. Their suggestions have helped to improve both the design
and presentation of the protocol. and presentation of the protocol.
skipping to change at page 69, line 31 skipping to change at page 86, line 31
[5] Stephen E. Deering and Robert M. Hinden. Internet [5] Stephen E. Deering and Robert M. Hinden. Internet
Protocol version 6 (IPv6) specification. Internet-Draft, Protocol version 6 (IPv6) specification. Internet-Draft,
draft-ietf-ipngwg-ipv6-spec-v2-00.txt, July 1997. Work in draft-ietf-ipngwg-ipv6-spec-v2-00.txt, July 1997. Work in
progress. progress.
[6] Paul Ferguson and Daniel Senie. Network ingress filtering: [6] Paul Ferguson and Daniel Senie. Network ingress filtering:
Defeating denial of service attacks which employ IP source Defeating denial of service attacks which employ IP source
address spoofing. RFC 2267, January 1998. address spoofing. RFC 2267, January 1998.
[7] Stephen Kent and Randall Atkinson. IP Authentication header. [7] Robert M. Hinden and Stephen E. Deering. IP Version 6
addressing architecture. Internet-Draft,
draft-ietf-ipngwg-addr-arch-v2-06.txt, January 1998. Work in
progress.
[8] Stephen Kent and Randall Atkinson. IP Authentication header.
Internet-Draft, draft-ietf-ipsec-auth-header-02.txt, October Internet-Draft, draft-ietf-ipsec-auth-header-02.txt, October
1997. Work in progress. 1997. Work in progress.
[8] Stephen Kent and Randall Atkinson. IP Encapsulating Security [9] Stephen Kent and Randall Atkinson. IP Encapsulating Security
Payload (ESP). Internet-Draft, draft-ietf-ipsec-esp-v2-01.txt, Payload (ESP). Internet-Draft, draft-ietf-ipsec-esp-v2-01.txt,
October 1997. Work in progress. October 1997. Work in progress.
[9] P. Mockapetris. Domain Names---concepts and facilities. [10] Stephen Kent and Randall Atkinson. Security architecture for
the Internet Protocol. Internet-Draft,
draft-ietf-ipsec-arch-sec-02.txt, November 1997. Work in
progress.
[11] P. Mockapetris. Domain Names -- concepts and facilities.
RFC 1034, November 1987. RFC 1034, November 1987.
[10] P. Mockapetris. Domain Names---implementation and [12] P. Mockapetris. Domain Names -- implementation and
specification. RFC 1035, November 1987. specification. RFC 1035, November 1987.
[11] Thomas Narten, Erik Nordmark, and William Allen Simpson. [13] Thomas Narten, Erik Nordmark, and William Allen Simpson.
Neighbor Discovery for IP version 6 (IPv6). Internet-Draft, Neighbor Discovery for IP version 6 (IPv6). Internet-Draft,
draft-ietf-ipngwg-discovery-v2-00.txt, July 1997. Work in draft-ietf-ipngwg-discovery-v2-00.txt, July 1997. Work in
progress. progress.
[12] Charles Perkins. IP encapsulation within IP. RFC 2003, October [14] Charles Perkins. IP encapsulation within IP. RFC 2003, October
1996. 1996.
[13] Charles Perkins, editor. IP mobility support. RFC 2002, [15] Charles Perkins, editor. IP mobility support. RFC 2002,
October 1996. October 1996.
[14] Charles Perkins. Minimal encapsulation within IP. RFC 2004, [16] Charles Perkins. Minimal encapsulation within IP. RFC 2004,
October 1996. October 1996.
[15] J. B. Postel. User Datagram Protocol. RFC 768, August 1980. [17] Charles Perkins and David B. Johnson. Route optimization in
Mobile IP. Internet-Draft, draft-ietf-mobileip-optim-07.txt,
November 1997. Work in progress.
[16] J. B. Postel, editor. Transmission Control Protocol. RFC 793, [18] David C. Plummer. An Ethernet address resolution protocol:
Or converting network protocol addresses to 48.bit Ethernet
addresses for transmission on Ethernet hardware. RFC 826,
November 1982.
[19] J. B. Postel. User Datagram Protocol. RFC 768, August 1980.
[20] J. B. Postel, editor. Transmission Control Protocol. RFC 793,
September 1981. September 1981.
[17] Joyce K. Reynolds and Jon Postel. Assigned numbers. RFC 1700, [21] Joyce K. Reynolds and Jon Postel. Assigned numbers. RFC 1700,
October 1994. October 1994.
[18] Susan Thomson and Thomas Narten. IPv6 stateless address [22] Susan Thomson and Thomas Narten. IPv6 stateless address
autoconfiguration. Internet-Draft, autoconfiguration. Internet-Draft,
draft-ietf-ipngwg-addrconf-v2-00.txt, July 1997. draft-ietf-ipngwg-addrconf-v2-00.txt, July 1997.
Chair's Address Chair's Address
The Working Group can be contacted via its current chairs: The Working Group can be contacted via its current chairs:
Jim Solomon Jim Solomon
Motorola, Inc. RedBack Networks
1301 E. Algonquin Rd. 1389 Moffett Park Drive
Schaumburg, IL 60196 Sunnyvale, CA 94089-1134
USA USA
Phone: +1 847 576-2753 Phone: +1 408 548-3583
E-mail: solomon@comm.mot.com Fax: +1 408 548-3599
E-mail: solomon@rback.com
Erik Nordmark Erik Nordmark
Sun Microsystems, Inc. Sun Microsystems, Inc.
2550 Garcia Avenue 2550 Garcia Avenue
Mt. View, CA 94041 Mt. View, CA 94041
USA USA
Phone: +1 415 786-5166 Phone: +1 415 786-5166
Fax: +1 415 786-5896 Fax: +1 415 786-5896
E-mail: nordmark@sun.com E-mail: nordmark@sun.com
 End of changes. 

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