draft-ietf-mobileip-ipv6-02.txt   draft-ietf-mobileip-ipv6-03.txt 
Mobile IP Working Group David B. Johnson Mobile IP Working Group David B. Johnson
INTERNET-DRAFT Carnegie Mellon University INTERNET-DRAFT Carnegie Mellon University
Charles Perkins Charles Perkins
IBM Corporation Sun Microsystems
26 November 1996 30 July 1997
Mobility Support in IPv6 Mobility Support in IPv6
<draft-ietf-mobileip-ipv6-02.txt> <draft-ietf-mobileip-ipv6-03.txt>
Abstract
This document specifies the operation of mobile computers using IPv6.
Each mobile node is always identified by its home address, regardless
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
address, which provides information about the mobile node's current
location. IPv6 packets addressed to a mobile node's home address are
transparently routed to its care-of address. The protocol enables
IPv6 nodes to cache the binding of a mobile node's home address with
its care-of address, and to then send packets destined for the mobile
node directly to it at this care-of address.
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
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
To learn the current status of any Internet-Draft, 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
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Contents Abstract
Abstract i This document specifies the operation of mobile computers using IPv6.
Each mobile node is always identified by its home address, regardless
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
address, which provides information about the mobile node's current
location. IPv6 packets addressed to a mobile node's home address are
transparently routed to its care-of address. The protocol enables
IPv6 nodes to cache the binding of a mobile node's home address with
its care-of address, and to then send packets destined for the mobile
node directly to it at this care-of address.
Contents
Status of This Memo i Status of This Memo i
Abstract i
1. Introduction 1 1. Introduction 1
2. Terminology 2 2. Terminology 2
2.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 2 2.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 2
2.2. Mobile IPv6 Terms . . . . . . . . . . . . . . . . . . . . 3 2.2. Mobile IPv6 Terms . . . . . . . . . . . . . . . . . . . . 3
2.3. Specification Language . . . . . . . . . . . . . . . . . 4 2.3. Specification Language . . . . . . . . . . . . . . . . . 4
3. Overview of Mobile IPv6 Operation 6 3. Overview of Mobile IPv6 Operation 6
3.1. Protocol Summary . . . . . . . . . . . . . . . . . . . . 6
3.2. Comparison with Mobile IP for IPv4 . . . . . . . . . . . 11
4. New IPv6 Destination Options 11 4. New IPv6 Destination Options 12
4.1. Binding Update Option . . . . . . . . . . . . . . . . . . 11 4.1. Binding Update Option . . . . . . . . . . . . . . . . . . 12
4.2. Binding Acknowledgement Option . . . . . . . . . . . . . 14 4.2. Binding Acknowledgement Option . . . . . . . . . . . . . 16
4.3. Binding Request Option . . . . . . . . . . . . . . . . . 17 4.3. Binding Request Option . . . . . . . . . . . . . . . . . 20
4.4. Home Address Option . . . . . . . . . . . . . . . . . . . 21
5. Requirements for IPv6 Nodes 18 5. Requirements for IPv6 Nodes 23
6. Correspondent Node Operation 20 6. Correspondent Node Operation 25
6.1. Receiving Binding Updates . . . . . . . . . . . . . . . . 20 6.1. Receiving Packets from a Mobile Node . . . . . . . . . . 25
6.2. Requests to Cache a Binding . . . . . . . . . . . . . . . 21 6.2. Receiving Binding Updates . . . . . . . . . . . . . . . . 25
6.3. Requests to Delete a Binding . . . . . . . . . . . . . . 21 6.3. Requests to Cache a Binding . . . . . . . . . . . . . . . 26
6.4. Sending Binding Acknowledgements . . . . . . . . . . . . 21 6.4. Requests to Delete a Binding . . . . . . . . . . . . . . 27
6.5. Cache Replacement Policy . . . . . . . . . . . . . . . . 22 6.5. Sending Binding Acknowledgements . . . . . . . . . . . . 27
6.6. Receiving ICMP Error Messages . . . . . . . . . . . . . . 23 6.6. Cache Replacement Policy . . . . . . . . . . . . . . . . 28
6.7. Sending Packets to a Mobile Node . . . . . . . . . . . . 24 6.7. Receiving ICMP Error Messages . . . . . . . . . . . . . . 28
6.8. Sending Packets to a Mobile Node . . . . . . . . . . . . 29
7. Home Agent Operation 26 7. Home Agent Operation 31
7.1. Primary Care-of Address Registration . . . . . . . . . . 26 7.1. Dynamic Home Agent Address Discovery . . . . . . . . . . 31
7.2. Primary Care-of Address De-registration . . . . . . . . . 28 7.2. Primary Care-of Address Registration . . . . . . . . . . 31
7.3. Tunneling Intercepted Packets to a Mobile Node . . . . . 28 7.3. Primary Care-of Address De-registration . . . . . . . . . 33
7.4. Renumbering the Home Subnet . . . . . . . . . . . . . . . 29 7.4. Tunneling Intercepted Packets to a Mobile Node . . . . . 34
7.5. Renumbering the Home Subnet . . . . . . . . . . . . . . . 35
8. Mobile Node Operation 31 8. Mobile Node Operation 37
8.1. Movement Detection . . . . . . . . . . . . . . . . . . . 31 8.1. Sending Packets While Away from Home . . . . . . . . . . 37
8.2. Forming New Care-of Addresses . . . . . . . . . . . . . . 33 8.2. Movement Detection . . . . . . . . . . . . . . . . . . . 38
8.3. Sending Binding Updates to the Home Agent . . . . . . . . 34 8.3. Forming New Care-of Addresses . . . . . . . . . . . . . . 40
8.4. Sending Binding Updates to Correspondent Nodes . . . . . 35 8.4. Sending Binding Updates to the Home Agent . . . . . . . . 41
8.5. Sending Binding Updates to the Previous Default Router . 37 8.5. Sending Binding Updates to Correspondent Nodes . . . . . 42
8.6. Retransmitting Binding Updates . . . . . . . . . . . . . 37 8.6. Sending Binding Updates to the Previous Default Router . 45
8.7. Rate Limiting for Sending Binding Updates . . . . . . . . 38 8.7. Retransmitting Binding Updates . . . . . . . . . . . . . 45
8.8. Receiving Binding Acknowledgements . . . . . . . . . . . 38 8.8. Rate Limiting for Sending Binding Updates . . . . . . . . 46
8.9. Using Multiple Care-of Addresses . . . . . . . . . . . . 39 8.9. Receiving Binding Acknowledgements . . . . . . . . . . . 46
8.10. Returning Home . . . . . . . . . . . . . . . . . . . . . 39 8.10. Using Multiple Care-of Addresses . . . . . . . . . . . . 47
8.11. Returning Home . . . . . . . . . . . . . . . . . . . . . 47
9. Routing Multicast Packets 41 9. Routing Multicast Packets 49
10. Constants 42 10. Constants 50
11. Security Considerations 43 11. Security Considerations 51
11.1. Binding Updates, Acknowledgements, and Requests . . . . . 51
11.2. Home Address Options . . . . . . . . . . . . . . . . . . 51
11.3. General Mobile Computing Issues . . . . . . . . . . . . . 52
Acknowledgements 44 Appendix A. Changes from Previous Draft 53
A. Open Issues 45 Acknowledgements 54
A.1. Session Keys with Local Routers . . . . . . . . . . . . . 45
A.2. Source Address Filtering by Firewalls . . . . . . . . . . 45
A.3. Dynamic Home Agent Address Discovery . . . . . . . . . . 46
A.4. Replay Protection for Binding Updates . . . . . . . . . . 46
References 47 References 55
Chair's Address 49 Chair's Address 57
Authors' Addresses 50 Authors' Addresses 58
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 for Internet Protocol Version 6 (IPv6) [5]. Without specific support for
mobility in IPv6, packets destined to a mobile node (host or router) 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 from its would not be able to reach it while the mobile node is away from its
home IPv6 subnet, since routing is based on the network prefix in a home IPv6 subnet, since routing is based on the network prefix in a
packet's destination IP address. In order continue communication packet's destination IP address. In order continue communication
in spite of its movement, a mobile node could change its IP address in spite of its movement, a mobile node could change its IP address
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then not be able to maintain transport and higher-layer connections then not be able to maintain transport and higher-layer connections
when it changes location. Mobility support in IPv6 is particularly when it changes location. Mobility support in IPv6 is particularly
important, as mobile computers are likely to account for a majority important, as mobile computers are likely to account for a majority
or at least a substantial fraction of the population of the Internet or at least a substantial fraction of the population of the Internet
during the lifetime of IPv6. during the lifetime of IPv6.
The protocol operation defined here, known as Mobile IPv6, allows a The protocol operation defined here, known as Mobile IPv6, allows a
mobile node to move from one IPv6 subnet to another without changing mobile node to move from one IPv6 subnet to another without changing
the mobile node's IP address. A mobile node is always addressable the mobile node's IP address. A mobile node is always addressable
by its "home address", the IP address assigned to the mobile node by its "home address", the IP address assigned to the mobile node
within its home IPv6 subnet. Packets may be routed to it using this within its home IPv6 subnet. Packets may be routed to the mobile
address regardless of the mobile node's current point of attachment node using this address regardless of the mobile node's current point
to the Internet, and the mobile node may continue to communicate with of attachment to the Internet, and the mobile node may continue to
other nodes (stationary or mobile) after moving to a new subnet. communicate with other nodes (stationary or mobile) after moving
The movement of a mobile node away from its home subnet is thus to a new subnet. The movement of a mobile node away from its home
transparent to transport and higher-layer protocols and applications. subnet is thus transparent to transport and higher-layer protocols
and applications.
The Mobile IPv6 protocol is just as suitable for mobility across The Mobile IPv6 protocol is just as suitable for mobility across
homogeneous media as for mobility across heterogeneous media. For homogeneous media as for mobility across heterogeneous media. For
example, Mobile IPv6 facilitates node movement from one Ethernet example, Mobile IPv6 facilitates node movement from one Ethernet
segment to another as well as it accommodates node movement from an segment to another as well as it facilitates node movement from an
Ethernet segment to a wireless LAN cell, as long as the mobile node's Ethernet segment to a wireless LAN cell, with the mobile node's IP
IP address remains unchanged after such a movement. address remaining unchanged in spite of such movement.
One can think of the Mobile IPv6 protocol as solving the "macro" One can think of the Mobile IPv6 protocol as solving the "macro"
mobility management problem. More "micro" mobility management mobility management problem. More "micro" mobility management
applications -- for example, handoff amongst wireless transceivers, applications -- for example, handoff amongst wireless transceivers,
each of which covers only a very small geographic area, are possibly each of which covers only a very small geographic area -- are
more suited to other solutions. For example, as long as node possibly more suited to other solutions. For example, as long as
movement does not occur between link-level points of attachment on node movement does not occur between link-level points of attachment
different IPv6 subnets, link-layer mobility support offered by a on different IPv6 subnets, link-layer mobility support offered by a
number of current wireless LAN products is likely to offer faster number of current wireless LAN products is likely to offer faster
convergence and lower overhead than Mobile IPv6. Extensions to the convergence and lower overhead than Mobile IPv6. Extensions to the
Mobile IPv6 protocol are also possible to support a more local, Mobile IPv6 protocol are also possible to support a more local,
hierarchical form of handoff, but such extensions are beyond the sope hierarchical form of handoff, but such extensions are beyond the sope
of this document. of this document.
2. Terminology 2. Terminology
2.1. General Terms 2.1. General Terms
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home subnet home subnet
The IP subnet indicated by a mobile node's home address. The IP subnet indicated by a mobile node's home address.
Standard IP routing mechanisms will deliver packets destined Standard IP routing mechanisms will deliver packets destined
for a mobile node's home address to its home subnet. for a mobile node's home address to its home subnet.
mobile node mobile node
A node that can change its link-level point of attachment from A node that can change its link-level point of attachment from
one IP subnet to another, while still being addressable via its one IP subnet to another, while still being reachable via its
home address. home address.
movement movement
A change in a mobile node's point of attachment to the Internet A change in a mobile node's point of attachment to the Internet
such that it is no longer link-level connected to the same IP such that it is no longer link-level connected to the same IP
subnet as it was previously. If a mobile node is not currently subnet as it was previously. If a mobile node is not currently
link-level connected to its home subnet, the mobile node is link-level connected to its home subnet, the mobile node is
said to be "away from home". said to be "away from home".
correspondent node correspondent node
A peer with which a mobile node is communicating. The A peer node with which a mobile node is communicating. The
correspondent node may be either mobile or stationary. correspondent node may be either mobile or stationary.
foreign subnet foreign subnet
Any IP subnet other than the mobile node's home subnet. Any IP subnet other than the mobile node's home subnet.
home agent home agent
A router on a mobile node's home subnet with which the mobile A router on a mobile node's home subnet with which the mobile
node has registered its current care-of address. While the node has registered its current care-of address. While the
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packets on the home subnet destined to the mobile node's home packets on the home subnet destined to the mobile node's home
address, encapsulates them, and tunnels them to the mobile address, encapsulates them, and tunnels them to the mobile
node's registered care-of address. node's registered care-of address.
care-of address care-of address
An IP address associated with a mobile node while visiting An IP address associated with a mobile node while visiting
a foreign subnet, which uses the network prefix of that a foreign subnet, which uses the network prefix of that
foreign subnet. Among the multiple care-of addresses that a foreign subnet. Among the multiple care-of addresses that a
mobile node may have at a time (e.g., with different network mobile node may have at a time (e.g., with different network
prefixes), the one registered with its home agent is called its prefixes), the one registered with the mobile node's home agent
"primary" care-of address. is called its "primary" care-of address.
binding binding
The association of the home address of a mobile node with a The association of the home address of a mobile node with a
care-of address for that mobile node, along with the remaining care-of address for that mobile node, along with the remaining
lifetime of that association. lifetime of that association.
2.3. Specification Language 2.3. Specification Language
In this document, several words are used to signify the requirements In this document, several words are used to signify the requirements
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silently discard silently discard
The implementation discards the packet without further The implementation discards the packet without further
processing, and without indicating an error to the sender. The processing, and without indicating an error to the sender. The
implementation SHOULD provide the capability of logging the implementation SHOULD provide the capability of logging the
error, including the contents of the discarded packet, and error, including the contents of the discarded packet, and
SHOULD record the event in a statistics counter. SHOULD record the event in a statistics counter.
3. Overview of Mobile IPv6 Operation 3. Overview of Mobile IPv6 Operation
3.1. Protocol Summary
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 subnet or is away from home. While is currently attached to its home subnet or is away from home. While
a mobile node is at home, packets addressed to the mobile node's a mobile node is at home, packets addressed to the mobile node's
home address are routed to it using conventional Internet routing home address are routed to it using conventional Internet routing
mechanisms in the same way as if the node were never mobile. Since mechanisms in the same way as if the node were never mobile. Since
the network prefix of a mobile node's home address is equal to the the network prefix of a mobile node's home address is equal to the
network prefix of its home subnet, packets addressed to it will be network prefix of its home subnet, packets addressed to it will be
routed to its home subnet. routed to its home subnet.
While a mobile node is attached to some foreign subnet away from While a mobile node is attached to some foreign subnet away from
home, it is also addressable by one or more care-of addresses, in home, it is also addressable by one or more care-of addresses, in
addition to its home address. A care-of address is an IP address addition to its home address. A care-of address is an IP address
associated with a mobile node only while visiting a particular associated with a mobile node while visiting a particular foreign
foreign subnet. The network prefix of a care-of address being used subnet. The network prefix of a mobile node's care-of address is
by a mobile node is equal to the network prefix of the foreign equal to the network prefix of the foreign subnet being visited
subnet to which the mobile node is link-level connected, and thus by the mobile node; if the mobile node is link-level connected
packets addressed to this care-of address will be routed to the to this foreign subnet while using that care-of address, packets
mobile node's location away from home. The association between addressed to this care-of address will be routed to the mobile node
a mobile node's home address and care-of address is known as a in its location away from home. The association between a mobile
"binding" for the mobile node. A mobile node typically acquires its node's home address and care-of address is known as a "binding"
care-of address through stateless [14] or stateful (e.g., DHCPv6 [3]) for the mobile node. A mobile node typically acquires its care-of
address through stateless [16] or stateful (e.g., DHCPv6 [3])
address autoconfiguration, according to the methods of IPv6 Neighbor address autoconfiguration, according to the methods of IPv6 Neighbor
Discovery [8], although other methods of acquiring a care-of address Discovery [9], although other methods of acquiring a care-of address
are also possible. are also possible.
While away from home, the mobile node registers one of its binding While away from home, the mobile node registers one of its bindings
with a router in its home subnet, requesting this router to function with a router in its home subnet, requesting this router to function
as the "home agent" for the mobile node. The care-of address in this as the "home agent" for the mobile node. This binding registration
binding registered with its home agent is known as the mobile node's is done by the mobile node sending a packet with a "Binding Update"
"primary care-of address". The mobile node's home agent thereafter destination option to the home agent, which replies by returning a
uses proxy Neighbor Discovery to intercept any IPv6 packets addressed packet containing a "Binding Acknowledgement" destination option to
to the mobile node's home address on the home subnet, and tunnels the mobile node. The care-of address in this binding registered
each intercepted packet to the mobile node's primary care-of address. with its home agent is known as the mobile node's "primary care-of
address". The mobile node's home agent thereafter uses proxy
Neighbor Discovery to intercept any IPv6 packets addressed to the
mobile node's home address on the home subnet, and tunnels each
intercepted packet to the mobile node's primary care-of address.
To tunnel each intercepted packet, the home agent encapsulates the To tunnel each intercepted packet, the home agent encapsulates the
packet using IPv6 encapsulation [4], addressed to the mobile node's packet using IPv6 encapsulation [4], addressed to the mobile node's
primary care-of address. primary care-of address.
Mobile IPv6 provides a mechanism for IPv6 nodes communicating with The Binding Update and Binding Acknowledgement destination options,
a mobile node, to dynamically learn and cache the mobile node's together with a "Binding Request" destination option, are also used
binding. When sending a packet to any IPv6 destination, a node to allow IPv6 nodes communicating with a mobile node, to dynamically
checks its cached bindings for an entry for the packet's destination learn and cache the mobile node's binding. When sending a packet
address. If a cached binding for this destination address is to any IPv6 destination, a node checks its cached bindings for an
found, the node uses an IPv6 Routing header [5] (instead of IPv6 entry for the packet's destination address. If a cached binding for
encapsulation) to route the packet to the mobile node through the this destination address is found, the node uses an IPv6 Routing
care-of address indicated in this binding. If, instead, the sending header [5] (instead of IPv6 encapsulation) to route the packet to
node has no cached binding for this destination address, the node the mobile node by way of the care-of address indicated in this
sends the packet normally (with no Routing header), and the packet binding. If, instead, the sending node has no cached binding for
is subsequently intercepted and tunneled by the mobile node's home this destination address, the node sends the packet normally (with
agent as described above. A node communicating with a mobile node is no Routing header), and the packet is subsequently intercepted and
referred to in this document as a "correspondent node" of the mobile tunneled by the mobile node's home agent as described above. A node
node. communicating with a mobile node is referred to in this document as a
"correspondent node" of the mobile node.
A mobile node's home agent and correspondent nodes learn and Since a Binding Update, Binding Acknowledgement, and Binding Request
cache the mobile node's binding through use of a set of new IPv6 are each represented in a packet as an IPv6 destination option [5],
destination options [5] defined for Mobile IPv6. Since an IPv6 they may be included in any IPv6 packet. Any of these options can be
Destination Options header containing one or more destination options sent in either of two ways:
can appear in any IPv6 packet, any Mobile IPv6 option can be sent in
either of two ways:
- A Mobile IPv6 option can be included within any IPv6 packet - A Binding Update, Binding Acknowledgement, or Binding Request can
carrying any payload such as TCP [11] or UDP [10]. be included within any IPv6 packet carrying any payload such as
TCP [14] or UDP [13].
- A Mobile IPv6 option can be sent as a separate IPv6 packet - A Binding Update, Binding Acknowledgement, or Binding Request can
containing no payload. In this case, the Next Header field be sent as a separate IPv6 packet containing no payload. In this
in the Destination Options header is set to the value 59, to case, the Next Header field in the Destination Options header is
indicate "No Next Header" [5]. set to the value 59, to indicate "No Next Header" [5].
The following three new IPv6 destination options are defined for Mobile IPv6 also defines one additional IPv6 destination option.
Mobile IPv6: 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
of its current care-of addresses, and will also include a "Home
Address" destination option in the packet, giving the mobile node's
home address. Many routers implement security policies such as
"ingress filtering" [6] that do not allow forwarding of packets
that appear to have a Source Address that is not topologically
correct. By using the care-of address as the IPv6 header Source
Address, the packet will be able to pass normally through such
routers, yet ingress filtering rules will still be able to locate
the true physical source of the packet in the same way as packets
from non-mobile nodes. By also including the Home Address option,
the sending mobile node can communicate its home address to the
correspondent node receiving this packet, allowing the use of the
care-of address to be transparent above the Mobile IPv6 support
level (e.g., at the transport layer). The inclusion of a Home
Address option in a packet affects only the correspondent node's
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
a packet.
In summary, the following four new IPv6 destination options are
defined for Mobile IPv6:
Binding Update Binding Update
A Binding Update is used by a mobile node to notify a A Binding Update option is used by a mobile node to notify
correspondent node or its home agent of its current binding. a correspondent node or the mobile node's home agent of
The Binding Update sent to the mobile node's home agent is its current binding. The Binding Update sent to the mobile
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 an IPv6 Authentication Binding Update option MUST also include an IPv6 Authentication
header [1]. The Binding Update option is described in detail header [1], providing sender authentication, data integrity
in Section 4.1. protection, and replay protection. The Binding Update option
is described in detail in Section 4.1.
Binding Acknowledgement Binding Acknowledgement
A Binding Acknowledgement is used to acknowledge receipt of A Binding Acknowledgement option is used to acknowledge receipt
a Binding Update, if an acknowledgement was requested in the of a Binding Update, if an acknowledgement was requested
Binding Update. Other Binding Updates MAY be acknowledged in the Binding Update. Any packet that includes a Binding
but need not be. Any packet that includes a Binding
Acknowledgement option MUST also include an IPv6 Authentication Acknowledgement option MUST also include an IPv6 Authentication
header [1]. The Binding Acknowledgement option is described in header [1], providing sender authentication, data integrity
detail in Section 4.2. protection, and replay protection. The Binding Acknowledgement
option is described in detail in Section 4.2.
Binding Request Binding Request
A Binding Request is used to request a mobile node to send a A Binding Request option is used to request a mobile node
Binding Update to this node, containing its current binding. to send a Binding Update to the requesting node, containing
the mobile node's current binding. This option is typically
used by a correspondent node to refresh a cached binding for
a mobile node, when the cached binding is in active use but
the binding's lifetime is close to expiration. No special
authentication is required for the Binding Request option. The
Binding Request option is described in detail in Section 4.3.
This option is typically used by a correspondent node to Home Address
refresh a cached binding for a mobile node, when the lifetime
on this cached binding is close to expiration. The Binding A Home Address option is used in a packet sent by a mobile
Request option is described in detail in Section 4.3. node to inform the recipient of that packet of the mobile
node's home address. For packets sent by a mobile node while
away from home, the mobile node generally uses one of its
care-of addresses as the Source Address in the packet's IPv6
header. By including a Home Address option in the packet, the
correspondent node receiving the packet is able to substitute
the mobile node's home address for this care-of address when
processing the packet, thus making the use of the care-of
address transparent to the correspondent node. The Home
Address option is described in detail in Section 4.4.
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.
This document describes the Mobile IPv6 protocol in terms of the This document describes the Mobile IPv6 protocol in terms of the
following two conceptual data structures used in the maintenance of following two conceptual data structures used in the maintenance of
cached bindings: cached bindings:
Binding Cache Binding Cache
A cache, maintained by each IPv6 node, of bindings for other A cache, maintained by each IPv6 node, of bindings for other
nodes. An entry in a node's binding cache for which the node nodes. An entry in a node's binding cache for which the node
is serving as a home agent is marked as a "home registration" is 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
expiration of its binding lifetime, whereas other Binding Cache expiration of its binding lifetime. Other Binding Cache
entries MAY be replaced at any time by any reasonable local entries MAY be replaced at any time by any reasonable local
cache replacement policy. The Binding Cache MAY be implemented cache replacement policy but SHOULD NOT be unnecessarily
in any manner consistent with the external behavior described deleted. Any node's Binding Cache may contain at most one
in this document, for example by being combined with the node's entry for each mobile node, keyed by the mobile node's home
Destination Cache as maintained through Neighbor Discovery [8]. address. The contents of a node's Binding Cache MUST NOT be
changed in response to a Home Address option in a received
packet. The Binding Cache MAY be implemented in any manner
consistent with the external behavior described in this
document, for example by being combined with the node's
Destination Cache as maintained through Neighbor Discovery [9].
Binding Update List Binding Update List
A list, maintained by each mobile node, recording information A list, maintained by each mobile node, recording information
for each Binding Update sent by this mobile node, for which for each Binding Update sent by this mobile node, for which the
the Lifetime of the binding sent in that Update has not yet Lifetime of the binding sent in that Binding Update has not
expired. For each such Binding Update, the Binding Update List yet expired. The Binding Update List includes all bindings
records the IP address of the node to which the Update was sent by the mobile node: those to correspondent nodes, to the
sent, the home address for which the Update was sent, and the mobile node's home agent, and to a previous default router
remaining lifetime of the binding. The Binding Update List of the mobile node. Each Binding Update List entry records
the IP address of the node to which the Update was sent, the
home address for which one Binding Update was sent, and the
remaining lifetime of that binding. The Binding Update List
MAY be implemented in any manner consistent with the external MAY be implemented in any manner consistent with the external
behavior described in this document. behavior described in this document.
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
skipping to change at page 9, line 34 skipping to change at page 10, line 43
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
the mobile node, that it will continue this communication in the the mobile node, that it will continue this communication in the
future. When a mobile node receives a Binding Request, it replies by future. When a mobile node receives a Binding Request, it replies by
returning a Binding Update to the node sending the Binding Request. returning a Binding Update to the node sending the Binding Request.
A mobile node may use more than one care-of address at the same time, A mobile node may use more than one care-of address at the same time,
although only one care-of address may be registered for it at its although only one care-of address may be registered for it at its
home agent as its primary care-of address. The mobile node's home home agent as its primary care-of address. The mobile node's home
agent will tunnel all intercepted packets for the mobile node to its agent will tunnel all intercepted packets for the mobile node to its
registered primary care-of address, but the mobile node will accept (single) registered primary care-of address, but the mobile node
packets that it receives at any of its current care-of addresses. will accept packets that it receives at any of its current care-of
Use of more than one care-of address by a mobile node may be useful, addresses. Use of more than one care-of address by a mobile node may
for example, to improve smooth handoff when the mobile node moves be useful, for example, to improve smooth handoff when the mobile
from one wireless IP subnet to another. If each wireless subnet is node moves from one wireless IP subnet to another. If each wireless
connected to the Internet through a separate base station, such that subnet is connected to the Internet through a separate base station,
the wireless transmission range from the two base stations overlap, such that the wireless transmission range from the two base stations
the mobile node may be able to remain link-level connected within overlap, the mobile node may be able to remain link-level connected
both subnets while in the area of overlap. In this case, the mobile within both subnets while in the area of overlap. In this case, the
node could acquire a new care-of address in the new subnet before mobile node could acquire a new care-of address in the new subnet
moving out of transmission range and link-level disconnecting from before moving out of transmission range and link-level disconnecting
the old subnet. The mobile node may thus still accept packets at from the old subnet. The mobile node may thus still accept packets
its old care-of address while it works to update its home agent and at its old care-of address while it works to update its home agent
correspondent nodes, notifying them of its new care-of address. and correspondent nodes, notifying them of its new care-of address in
the new subnet.
Since correspondent nodes cache bindings, it is expected that Since correspondent nodes cache bindings, it is expected that
correspondent nodes usually will route packets directly to the mobile correspondent nodes usually will route packets directly to the mobile
node's care-of address, so that the home agent is rarely involved node's care-of address, so that the home agent is rarely involved
with packet transmission to the mobile node. This is essential for with packet transmission to the mobile node. This is essential for
scalability and reliability, and for minimizing overall network load. scalability and reliability, and for minimizing overall network load.
By caching the care-of address of a mobile node, optimal routing of By caching the care-of address of a mobile node, optimal routing of
packets can be achieved from the correspondent node to the mobile packets can be achieved from the correspondent node to the mobile
node. Routing packets directly to the mobile node's care-of address node. Routing packets directly to the mobile node's care-of address
also eliminates congestion at the mobile node's home agent and home also eliminates congestion at the mobile node's home agent and home
subnet. In addition, the impact of of any possible failure of the subnet. In addition, the impact of of any possible failure of the
home agent, the home subnet, or intervening networks leading to the home agent, the home subnet, or intervening networks leading to or
home subnet is reduced, since these nodes and links are not involved from the home subnet is reduced, since these nodes and links are not
in the delivery of most packets to the mobile node. involved in the delivery of most packets to the mobile node.
3.2. Comparison with Mobile IP for IPv4
[This section will include a comparison between the Mobile IPv6
protocol and the Mobile IPv4 protocol [11, 10, 12]. However, this
comparison has not yet been written. It will be filled in with the
next revsion to this draft.]
4. New IPv6 Destination Options 4. New IPv6 Destination Options
4.1. Binding Update Option 4.1. Binding Update Option
The Binding Update destination option is used by a mobile node to The Binding Update destination option is used by a mobile node to
notify a correspondent node or its home agent of a new care-of notify a correspondent node or the mobile node's home agent of a new
address. care-of address.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L| Reserved | Lifetime | | Option Type | Option Length |A|H|C|L| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification | | Lifetime | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ Care-of Address + + Care-of Address +
| | | (only present if C bit set) |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ Home Link-Local Address + + Home Link-Local Address +
| (only present if L bit set) | | (only present if L bit set) |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type Option Type
192 ??? 192 ???
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, this field current definition of the Binding Update option, the minimum
MUST be set to 24 if the Home Link-Local Address Present (L) value for this field is 6, for the case in which neither the
bit is not set, and MUST otherwise be set to 40. Care-of Address Present (C) bit nor the Home Link-Local Address
Present (L) bit are set, and the maximum value is 38, for the
case in which both of these bits are 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 node to request a
Binding Acknowledgement (Section 4.2) be returned upon receipt Binding Acknowledgement (Section 4.2) be returned upon receipt
of the Binding Update option. of the Binding Update option.
Home Registration (H) Home Registration (H)
The Home Registration (H) bit is set by the sending node to The Home Registration (H) bit is set by the sending node to
request the receiving node to act as this node's home agent. request the receiving node to act as this node's home agent.
The Destination Address in the IP header of the packet carrying The Destination Address in the IP header of the packet carrying
this option MUST be that of a router sharing the same network this option MUST be that of a router sharing the same network
prefix as the home address of the mobile node in the binding. prefix as the home address of the mobile node in the binding
(given by the Home Address field in the Home Address option in
the packet).
Care-of Address Present (C)
The Care-of Address Present (C) bit indicates the presence 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 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
set.
Home Link-Local Address Present (L) Home Link-Local Address Present (L)
The Home Link-Local Address Present (L) bit indicates the The Home Link-Local Address Present (L) bit indicates the
presence of the Home Link-Local Address field in the Binding presence of the Home Link-Local Address field in the Binding
Update. This bit is set by the sending node to request Update. This bit is set by the sending node to request
the receiving node to act as a proxy (for participating in the receiving node to act as a proxy (for participating in
the Neighbor Discovery Protocol) for the node while it is the Neighbor Discovery Protocol) for the node while it is
away from home. This bit MUST NOT be set unless the Home away from home. This bit MUST NOT be set unless the Home
Registration (H) bit is also set in the Binding Update. Registration (H) bit is also set in the Binding Update.
skipping to change at page 12, line 41 skipping to change at page 14, line 5
Sent as 0; ignored on reception. Sent as 0; ignored on reception.
Lifetime Lifetime
16-bit unsigned integer. The number of seconds remaining 16-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
ones (0xffff) indicates infinity. A value of zero indicates ones (0xffff) indicates infinity. A value of zero indicates
that the Binding Cache entry for the mobile node should be that the Binding Cache entry for the mobile node should be
deleted. deleted.
Identification Sequence Number
a 32-bit number used by the receiving node to sequence Binding Used by the receiving node to sequence Binding Updates and by
Updates, and by the sending node to match a returned Binding the sending node to match a returned Binding Acknowledgement
Acknowledgement message with this Binding Update. with this Binding Update. Each Binding Update sent by a mobile
node MUST use a Sequence Number greater than the Sequence
Number value sent in the previous Binding Update (if any) to
the same destination address (modulo 2**16). There is no
requirement, however, that the Sequence Number value strictly
increase by 1 with each new Binding Update sent.
Care-of Address Care-of Address
The care-of address of the mobile node for this binding. When This field in the Binding Update is optional and is only
set equal to the home address of the mobile node, the Binding present when the Care-of Address Present (L) bit is set. If
Update option instead indicates that any existing binding for present, it gives the care-of address of the mobile node for
the mobile node should be deleted; no binding for the mobile this binding. For most Binding Updates sent, it is expected
node should be created in this case. that this field will not be present, and instead that the
care-of address for the binding will be given by the Source
Address field in the packet's IPv6 header.
Home Link-Local Address Home Link-Local Address
The link-local address of the mobile node used by the mobile This field in the Binding Update is optional and is only
node when it was last attached to its home subnet. This field present when the Home Link-Local Address Present (L) bit is
in the Binding Update is optional and is only present when the set. If present, it gives the link-local address of the mobile
Home Link-Local Address (L) bit is set. node used by the mobile node when it was last attached to its
home subnet.
The home address of the mobile node in the binding is indicated by Any packet including a Binding Update option MUST also include a Home
the Source Address field in the IP header of the packet containing Address option. The home address of the mobile node in the binding
the Binding Update option. given in the Binding Update option is indicated by the Home Address
field in the Home Address option in the packet.
Any packet that includes a Binding Update option MUST include an IPv6 Any packet that includes a Binding Update option MUST include an IPv6
Authentication header [1] in order to protect against forged Binding Authentication header [1] in order to protect against forged Binding
Updates. Updates. The authentication MUST provide sender authentication, data
integrity protection, and replay protection.
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
the packet's IPv6 header) is equal to the home address of the mobile
node, the Binding Update option indicates that any existing binding
for the mobile node should be deleted. Likewise, if the Lifetime
field in the Binding Update option is equal to 0, the Binding Update
option indicates that any existing binding for the mobile node should
be deleted. In each of these cases, no Binding Cache entry for the
mobile node should be created in response to receiving the Binding
Update.
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 the Update option, these three bits are set to 110, indicating 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, and that any IPv6 node processing this option that does destination, and that any IPv6 node processing this option that does
not recognize the Option Type must discard the packet and, only if not recognize the Option Type must discard the packet and, only if
the packet's Destination Address was not a multicast address, return the packet's Destination Address was not a multicast address, return
an ICMP Parameter Problem, Code 2, message to the packet's Source an ICMP Parameter Problem, Code 2, message to the packet's Source
Address. Address.
Extensions to the Binding Update option format may be included after Extensions to the Binding Update option format may be included after
the fixed portion of the Binding Update option specified above. The the fixed portion of the Binding Update option specified above. The
presence of such extensions will be indicated by the Option Length presence of such extensions will be indicated by the Option Length
field. When the Option Length is greater than 24 octets if the Home field. When the Option Length is greater than the length defined
Link-Local Address (L) bit is not set, or greater than 40 octets if above, depending on the state of the Care-of Address Present (C)
the Home Link-Local Address (L) bit is set, the remaining octets and Home Link-Local Address Present (L) bits, the remaining octets
are interpreted as extensions. Currently, no extensions have been are interpreted as extensions. Currently, no extensions have been
defined. defined.
4.2. Binding Acknowledgement Option 4.2. Binding Acknowledgement Option
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 4.1). When a node receipt of a Binding Update option (Section 4.1). When a node
receives a Binding Update addressed to itself, in which the receives a packet containing a Binding Update option, with this
Acknowledge (A) bit set, it MUST return a Binding Acknowledgement. node being the destination node of the packet, this node MUST
return a Binding Acknowledgement to the source of the packet, if the
Acknowledge (A) bit is set in the Binding Update.
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 Length | Status | | Option Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Refresh | Lifetime | | Option Length | Status | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification | | Refresh | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type Option Type
193 ??? 193 ???
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 Acknowledgement option, this current definition of the Binding Acknowledgement option, this
field MUST be set to 8. field MUST be set to 9.
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
Values of the Status field greater than or equal to 128 Values of the Status field greater than or equal to 128
indicate that the Binding Update was rejected by the receiving indicate that the Binding Update was rejected by the receiving
node. The following such Status values are currently defined: node. The following such Status values are currently defined:
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 Identification field mismatch 134 Sequence Number field value too small
135 Unknown home agent address 135 Dynamic home agent address discovery response
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" [12]. the most recent "Assigned Numbers" [15].
Refresh
The recommended period at which the mobile node should send
a new Binding Update to this node in order to "refresh" the
mobile node's binding in this node's binding cache, in case
the node fails and loses its cache state. The Refresh period
is determined by the node sending the Binging Acknowledgement
(the node caching the binding). If this node is serving as the
mobile node's home agent, the Refresh value may be set, for
example, based on whether the node stores the mobile node's
binding in volatile storage or in nonvolatile storage. If the
node sending the Binding Acknowledgement is not serving as the
mobile node's home agent, the Refresh period SHOULD be set
equal to the Lifetime period in the Binding Acknowledgement;
even if this node loses this cache entry due to a failure of
the node, packets from it can still reach the mobile node
through the mobile node's home agent, causing a new Binding
Update to this node to allow it to recreate this cache entry.
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 to extend the Update to it before the expiration of this period, in order to
lifetime. extend the lifetime.
Identification Refresh
The acknowledgement Identification is copied from the Binding The recommended period at which the mobile node SHOULD send
Update option, for use by the mobile node in matching the a new Binding Update to this node in order to "refresh" the
acknowledgement with an outstanding Binding Update. mobile node's binding in this node's binding cache. This
refreshing of the binding is useful in case the node fails and
loses its cache state. The Refresh period is determined by
the node sending the Binding Acknowledgement (the node caching
the binding). If this node is serving as the mobile node's
home agent, the Refresh value may be set, for example, based on
whether the node stores the mobile node's binding in volatile
storage or in nonvolatile storage. If the node sending the
Binding Acknowledgement is not serving as the mobile node's
home agent, the Refresh period SHOULD be set equal to the
Lifetime period in the Binding Acknowledgement; even if this
node loses this cache entry due to a failure of the node,
packets from it can still reach the mobile node through the
mobile node's home agent, causing a new Binding Update to this
node to allow it to recreate this cache entry.
Sequence Number
The Sequence Number in the Binding Acknowledgement is copied
from the Sequence Number field in the Binding Update option,
for use by the mobile node in matching this Acknowledgement
with an outstanding Binding Update.
Any packet that includes a Binding Acknowledgement option MUST Any packet that includes a Binding Acknowledgement option MUST
include an IPv6 Authentication header [1] in order to protect against include an IPv6 Authentication header [1] in order to protect
forged Binding Acknowledgements. against forged Binding Acknowledgements. The authentication MUST
provide sender 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 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 Cache, and MUST use this entry (which includes the care-of address
received in the Binding Update) in sending the packet containing the received in the Binding Update) in sending the packet containing the
Binding Acknowledgement to the mobile node. The details of sending Binding Acknowledgement to the mobile node. The details of sending
this packet to the mobile node are the same as for sending any packet this packet to the mobile node are the same as for sending any packet
to a mobile node using a Binding Cache entry, and are described in to a mobile node using a binding, and are described in Section 6.8.
Section 6.7. The packet is sent using a Routing header, routing the The packet is sent using a Routing header, routing the packet to the
packet to the mobile node through its care-of address recorded in the mobile node by way of its care-of address recorded in the Binding
Binding Cache entry. Cache entry.
If the node returning the Binding Acknowledgement instead If the node returning the Binding Acknowledgement instead
rejected the Binding Update (the value of the Status field in the rejected the Binding Update (the value of the Status field in the
Acknowledgement is greater than or equal to 128), this node MUST Acknowledgement is greater than or equal to 128), this node MUST
similarly use a Routing header in sending the packet containing the similarly use a Routing header in sending the packet containing the
Binding Acknowledgement, as described in Section 6.7, but MUST NOT Binding Acknowledgement, as described in Section 6.8, but MUST NOT
use its Binding Cache in forming the IP header or Routing header use its Binding Cache in forming the IP header or Routing header
in this packet. Rather, the care-of address used by this node in in this packet. Rather, the care-of address used by this node in
sending the packet containing the Binding Acknowledgement MUST be sending the packet containing the Binding Acknowledgement MUST be
copied from the care-of address received in the rejected Binding copied from the care-of address received in the rejected Binding
Update; this node MUST NOT modify its Binding Cache in response Update; this node MUST NOT modify its Binding Cache in response
to receiving this rejected Binding Update and MUST ignore its to receiving this rejected Binding Update and MUST ignore its
Binding Cache in sending the packet in which it returns this Binding Binding Cache in sending the packet in which it returns this Binding
Acknowledgement. The packet is sent using a Routing header, routing Acknowledgement. The packet is sent using a Routing header, routing
the packet to the Source Address of the rejected Binding Update the packet to the home address of the rejected Binding Update by way
through the care-of address indicated in the Binding Update. of the care-of address indicated in the packet containing the Binding
Update.
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
Acknowledgement option, these three bits are set to 110, indicating Acknowledgement option, these three bits are set to 110, indicating
that the data within the option cannot change en-route to the that the data within the option cannot change en-route to the
packet's final destination, and that any IPv6 node processing this packet's final destination, and that any IPv6 node processing this
option that does not recognize the Option Type must discard the option that does not recognize the Option Type must discard the
packet and, only if the packet's Destination Address was not a packet and, only if the packet's Destination Address was not a
multicast address, return an ICMP Parameter Problem, Code 2, message multicast address, return an ICMP Parameter Problem, Code 2, message
to the packet's Source Address. to the packet's Source Address.
skipping to change at page 17, line 10 skipping to change at page 20, line 10
option specified above. The presence of such extensions will be option specified above. The presence of such extensions will be
indicated by the Option Length field. When the Option Length is indicated by the Option Length field. When the Option Length is
greater than 8 octets, the remaining octets are interpreted as greater than 8 octets, the remaining octets are interpreted as
extensions. Currently, no extensions have been defined. extensions. Currently, no extensions have been defined.
4.3. Binding Request Option 4.3. Binding Request Option
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. When a mobile node receives
a packet containing a Binding Request option, it SHOULD return a a packet containing a Binding Request option, it SHOULD return a
Binding Update (Section 4.1) to that node. Binding Update (Section 4.1) 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type Option Type
194 ??? 194 ???
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 Acknowledgement option, this current definition of the Binding Request option, this field
field MUST be set to 0. MUST be set to 0.
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
Request option, these three bits are set to 110, indicating that the Request option, these three bits are set to 110, indicating 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, and that any IPv6 node processing this option that does destination, and that any IPv6 node processing this option that does
not recognize the Option Type must discard the packet and, only if not recognize the Option Type must discard the packet and, only if
the packet's Destination Address was not a multicast address, return the packet's Destination Address was not a multicast address, return
an ICMP Parameter Problem, Code 2, message to the packet's Source an ICMP Parameter Problem, Code 2, message to the packet's Source
Address. Address.
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.
4.4. Home Address Option
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
node's home address. For packets sent by a mobile node while
away from home, the mobile node generally uses one of its care-of
addresses as the Source Address in the packet's IPv6 header. By
including a Home Address option in the packet, the correspondent
node receiving the packet is able to substitute the mobile node's
home address for this care-of address when processing the packet,
thus making the use of the care-of address transparent to the
correspondent node.
The Home Address option is encoded in type-length-value (TLV) format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Home Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
195 ???
Option Length
8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields. For the
current definition of the Home Address option, this field MUST
be set to 8.
Home Address
The home address of the mobile node sending the packet.
The inclusion of a Home Address option in a packet affects only
the correspondent node's 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 a packet. In particular, the
receipt of a packet containing a Home Address option MUST NOT alter
the contents of the receiver's Binding Cache due to the presence of
the Home Address option, and the mapping between the home address
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,
except that if the IPv6 header of a packet is covered by
authentication, then that authentication MUST also cover the Home
Address option. If the packet carries no IP authentication, then the
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
altered during transit. Upon receipt of a packet containing a Home
Address option, the receiving node replaces the Source Address in
the IPv6 header with the Home Address in the Home Address option.
By requiring that any authentication of the IPv6 header also cover
the Home Address option, the security of the Source Address field in
the IPv6 header is not compromised by the presence of a Home Address
option. Security issues related to the Home Address option are
discussed further in Section 11.
The three highest-order bits of the Option Type are encoded to
indicate specific processing of the option [5]. For the Home Address
option, these three bits are set to 110, indicating that the data
within the option cannot change en-route to the packet's final
destination, and that any IPv6 node processing this option that does
not recognize the Option Type must discard the packet and, only if
the packet's Destination Address was not a multicast address, return
an ICMP Parameter Problem, Code 2, message to the packet's Source
Address.
Extensions to the Home Address option format may be included after
the fixed portion of the Home Address option specified above.
The presence of such extensions will be indicated by the Option
Length field. When the Option Length is greater than 8 octets,
the remaining octets are interpreted as extensions. Currently, no
extensions have been defined.
5. Requirements for IPv6 Nodes 5. 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 IPv6 nodes. This section summarizes those
requirements, identifying the functionality each requirement is requirements, identifying the functionality each requirement is
intended to support. Further details on this functionality is intended to support. Further details on this functionality is
provided in the following sections. provided in the following sections.
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, the following requirements pertain to all IPv6 nodes: mobile node, the following requirements pertain to all IPv6 nodes:
- Every IPv6 node SHOULD be able to process a received Binding - Every IPv6 node MUST be able to process a Home Address option
Update option, and to return a Binding Acknowledgement message if received in a packet.
requested.
- Every IPv6 node SHOULD be able to process a Binding Update option
received in a packet, and to return a Binding Acknowledgement
option if requested.
- 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.
In order for a mobile node to operate correctly while away from In order for a mobile node to operate correctly while away from
home, at least one IPv6 router in the mobile node's home subnet must home, at least one IPv6 router in the mobile node's home subnet must
function as a home agent for the mobile node. The following special function as a home agent for the mobile node. The following special
requirements pertain to all IPv6 routers capable of serving as a home requirements pertain to all IPv6 routers capable of serving as a home
agent: agent:
- Every home agent MUST be able to maintain a registry of mobile - Every home agent MUST be able to maintain an entry in its Binding
node bindings, recording each mobile node's primary care-of Cache for each mobile node for which it is serving as the home
address, for those mobile nodes for which it is serving as the agent. Each such Binding Cache entry records the mobile node's
home agent. binding with its primary care-of address and is marked as a "home
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) on the local subnet addressed to a mobile
node for which it is currently serving as the home agent while node for which it is currently serving as the home agent while
that mobile node is away from home. that 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.
- Every home agent MUST be able to return Binding Acknowledgements - Every home agent MUST be able to return a Binding Acknowledgement
in response to Binding Updates received from a mobile node. in response to a Binding Update received with the Acknowledge (A)
bit set.
- Every home agent MUST be able to accept packets addressed to the
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
agent address discovery.
Finally, the following requirements pertain all IPv6 nodes capable of Finally, the following requirements pertain all IPv6 nodes capable of
functioning as mobile nodes: 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 Updates, as
specified in Sections 8.3, 8.4, and 8.5; and MUST be able to specified in Sections 8.4, 8.5, and 8.6; and MUST be able to
receive and process Binding Acknowledgements, as specified in receive and process Binding Acknowledgements, as specified in
Section 8.8. Section 8.9.
- 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.
6. Correspondent Node Operation 6. 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.
The correspondent node, itself, may be fixed or mobile, and may The correspondent node, itself, may be fixed or mobile, and may
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.
6.1. Receiving Binding Updates 6.1. Receiving Packets from a Mobile Node
Packets sent by a mobile node while away from home generally include
a Home Address option. When a node receives a packet containing
a Home Address option, it MUST process the option in a manner
consistent with copying the Home Address field from the Home Address
option into the IPv6 header, replacing the original value of the
Source Address field there. Further processing of the packet (e.g.,
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
used in the packet. Since the sending mobile node uses its home
address at the transport layer when sending such a packet, the use of
the care-of address and Home Address option is thus transparent to
both the mobile node and the correspondent node above the level of
the Home Address option generation and processing.
6.2. 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 packet according to the following tests: node MUST validate the Binding Update according to the following
tests:
- The packet contains an IP Authentication header and the - The packet contains an IP Authentication header and the
authentication is valid [1]. The Authentication header is authentication is valid [1]. The Authentication header MUST
assumed to provide both authentication and integrity protection. provide sender authentication, integrity protection, and replay
protection.
- The Option Length field in the option is greater than or equal to - The Option Length field in the Binding Update option is greater
24 octets if the Home Link-Local Address (L) bit is not set, or than or equal to the length specified in Section 4.1.
greater or equal to 40 octets if the Home Link-Local Address (L)
bit is set.
- The Identification field is valid. - The Sequence Number field in the Binding Update option is greater
than the Sequence Number received in the previous Binding Update
for this home address, if any. The Sequence Number comparison is
performed modulo 2**16.
- The packet MUST contain a valid Home Address option. The home
address for the binding is specified by the Home Address field of
the Home Address option.
Any Binding Update not satisfying all of these tests MUST be silently Any Binding Update not satisfying all of these tests MUST be silently
ignored, although the remainder of the packet (i.e., other options, ignored, although the remainder of the packet (i.e., other options,
extension headers, or payload) SHOULD be processed normally according extension headers, or payload) SHOULD be processed normally according
to any procedure defined for that part of the packet. to any procedure defined for that part of the packet.
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
Home-Agents anycast address for a local subnet and this address
is assigned to one of this node's network interfaces, then the
mobile node sending this Binding Update is attempting dynamic
home agent address discovery. Processing for this type of
received Binding Update is described in Section 7.1. (If the
Destination Address is not assigned to one of this node's network
interfaces, then the packet would have been forwarded as a normal
packet and the Binding Update, as a destination option, would not
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 Source Address the specified Care-of Address is not equal to the home address
in the IP header of the packet carrying the Binding Update, for the binding, then this is a request to cache a binding for
then this is a request to cache a binding for the mobile node the mobile node. Processing for this type of received Binding
(the home address of the mobile node is specified by the Source Update is described in Section 6.3.
Address field in the packet's IP header). Processing for this
type of received Binding Update is described in Section 6.2.
- 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 Source Address field in the specified Care-of Address matches the home address for the
IP header of the packet carrying the Binding Update, then this is binding, then this is a request to delete the mobile node's
a request to delete the mobile node's binding (as above, the home cached binding. Processing for this type of received Binding
address of the mobile node is specified by the Source Address Update is described in Section 6.4.
field in the packet's IP header). Processing for this type of
received Binding Update is described in Section 6.3.
6.2. Requests to Cache a Binding 6.3. Requests to Cache a Binding
If a node receives a valid Binding Update requesting it to cache a If a node receives a valid Binding Update requesting it to cache a
binding for a mobile node, as specified in Section 6.1, then the node binding for a mobile node, as specified in Section 6.2, then the node
MUST examine the Home Registration (H) bit in the Binding Update MUST examine the Home Registration (H) bit in the Binding Update
to determine how to further process the Binding Update. If the to determine how to further process the Binding Update. If the
Home Registration (H) bit is set, the Binding Update is processed Home Registration (H) bit is set, the Binding Update is processed
according to the procedure specified in Section 7.1. according to the procedure specified in Section 7.2.
If the Home Registration (H) bit is not set, then the receiving node If the Home Registration (H) bit is not set, then the receiving node
SHOULD create a new entry in its Binding Cache for this mobile node SHOULD create a new entry in its Binding Cache for this mobile node
(or update its existing Binding Cache entry for this mobile node, if (or update its existing Binding Cache entry for this mobile node, if
such an entry already exists). The home address of the mobile node such an entry already exists). The home address of the mobile node
is taken from the Source Address field in the packet's IP header. is taken from the Home Address field in the packet's Home Address
The new Binding Cache entry records the association between this option. The new Binding Cache entry records the association between
address and the Care-of Address specified in the Binding Update. this address and the care-of address for the binding, as specified
The node must also begin a timer to delete this Binding Cache entry in either the Care-of Address field of the Binding Update or in the
after the expiration of the Lifetime period specified in the Binding Source Address field in the packet's IPv6 header. Any Binding Cache
Update. entry created or updated in response to processing this Binding
Update MUST be deleted after the expiration of the Lifetime period
specified in the Binding Update.
6.3. Requests to Delete a Binding 6.4. Requests to Delete a Binding
If a node receives a valid Binding Update requesting it to delete If a node receives a valid Binding Update requesting it to delete a
a binding for a mobile node, as specified in Section 6.1, then the cached binding for a mobile node, as specified in Section 6.2, then
node MUST examine the Home Registration (H) bit in the Binding Update the node MUST examine the Home Registration (H) bit in the Binding
to determine how to further process the Binding Update. If the Update to determine how to further process the Binding Update. If
Home Registration (H) bit is set, the Binding Update is processed the Home Registration (H) bit is set, the Binding Update is processed
according to the procedure specified in Section 7.2. according to the procedure specified in Section 7.3.
If the Home Registration (H) bit is not set, then the receiving node If the Home Registration (H) bit is not set, then the receiving node
MUST delete any existing entry in its Binding Cache for this mobile MUST delete any existing entry in its Binding Cache for this mobile
node. The home address of the mobile node is taken from the Source node. The home address of the mobile node is taken from the Home
Address field in the packet's IP header. Address field in the packet's Home Address option.
6.4. Sending Binding Acknowledgements 6.5. 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 message acknowledging receipt of the Binding Acknowledgement option acknowledging receipt of the Binding Update.
Update. If the node accepts the Binding Update and adds the binding If the node accepts the Binding Update and creates or updates an
contained in it to its Binding Cache, the Status field in the entry in its Binding Cache for this binding, the Status field in
Binding Acknowledgement MUST be set to a value less than 128; if the Binding Acknowledgement MUST be set to a value less than 128;
the node rejects the Binding Update and does not add the binding if the node rejects the Binding Update and does not create or
contained in it to its Binding Cache, 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 4.2 and Specific values for the Status field are described in Section 4.2 and
in the most recent "Assigned Numbers" [12]. in the most recent "Assigned Numbers" [15].
As described in Section 4.2, the packet in which the Binding As described in Section 4.2, the packet in which the Binding
Acknowledgement is returned MUST include an IPv6 Authentication Acknowledgement is returned MUST include an IPv6 Authentication
header [1] in order to protect against forged Binding header [1] in order to protect against forged Binding
Acknowledgements, and the packet MUST be sent using a Routing Acknowledgements, and the packet MUST be sent using a Routing
header through the care-of address contained in the Binding Update header in the same way as any other packet sent to a mobile node
being acknowledged. This ensures that the Binding Acknowledgement using a care-of address (even if the binding was not accepted), as
will be routed to the current location of the node sending the described in Section 6.8. The packet is routed first to the care-of
Binding Update, whether the Binding Update was accepted or rejected. address contained in the Binding Update being acknowledged, and
then to the mobile node's home address. This use of the Routing
header ensures that the Binding Acknowledgement will be routed to the
current location of the node sending the Binding Update, whether the
Binding Update was accepted or rejected.
6.5. Cache Replacement Policy 6.6. 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 which
the entry was created or was last updated. Conceptually, a node the entry was created or was 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 7.1) MUST NOT be deleted from the cache until registration" (Section 7.2) MUST NOT be deleted from the cache until
the expiration of its lifetime period. When attempting to add a new the expiration of its lifetime period. When attempting to add a
"home registration" entry in response to a Binding Update with the new "home registration" entry in response to a Binding Update with
Home Registration (H) bit set, if insufficient space exists (or can the Home Registration (H) bit set, if insufficient space exists (or
be reclaimed) in the node's Binding Cache, the node MUST reject the can be reclaimed) in the node's Binding Cache, the node MUST reject
Binding Update and SHOULD return a Binding Acknowledgement message the Binding Update and SHOULD return a Binding Acknowledgement to
to the sending mobile node, in which the Status field is set to 131 the sending mobile node, in which the Status field is set to 131
(Insufficient resources). When otherwise attempting to add a new (insufficient resources). When otherwise attempting to add a new
entry to its Binding Cache, a node MAY, if needed, choose to drop any entry to its Binding Cache, a node MAY, if needed, choose to drop any
entry already in its Binding Cache, other than a "home registration" entry already in its Binding Cache, other than a "home registration"
entry, in order to make space for the new entry. For example, a entry, in order to make space for the new entry. For example, a
"least-recently used" (LRU) strategy for cache entry replacement is "least-recently used" (LRU) strategy for cache entry replacement
likely to work well. among entries not marked as a "home registration" is likely to work
well.
If a packet is sent by a node to a destination for which it has Any binding dropped from a node's Binding Cache due to lack of cache
dropped the cache entry from its Binding Cache, the packet will be space will be rediscovered and a new cache entry created, if the
routed normally, leading to the mobile node's home subnet. There, binding is still in active use by the node for sending packets. If
the packet will be intercepted by the mobile node's home agent and the node sends a packet to a destination for which it has dropped the
tunneled to the mobile node's current primary care-of address. As entry from its Binding Cache, the packet will be routed normally,
when a Binding Cache entry is initially created, this indirect leading to the mobile node's home subnet. There, the packet will
routing to the mobile node through its home agent will result in the be intercepted by the mobile node's home agent and tunneled to the
mobile node sending a Binding Update to this sending node, allowing mobile node's current primary care-of address. As when a Binding
this node to add an entry again for this destination to its Binding Cache entry is initially created, this indirect routing to the mobile
Cache. node through its home agent will result in the mobile node sending
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
Binding Cache.
6.6. Receiving ICMP Error Messages 6.7. 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
mobile node's address (its home address), then the correspondent address of the packet, then the correspondent node uses a Routing
node uses a Routing header to deliver the packet to the mobile node header to deliver the packet to the mobile node through the care-of
through the care-of address recorded in the Binding Cache entry. Any address in the binding recorded in the Binding Cache entry. Any ICMP
ICMP error message caused by the packet on its way to the mobile node error message caused by the packet on its way to the mobile node will
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 subnet, where it will be intercepted by the mobile node's node's home subnet, where it will be intercepted by the mobile node's
home agent, encapsulated, and tunneled to the mobile node's care-of home agent, encapsulated, and tunneled to the mobile node's primary
address. Any ICMP error message caused by the packet on its way to care-of address. Any ICMP error message caused by the packet on
the mobile node while in the tunnel, will be returned to the mobile its way to the mobile node while in the tunnel, will be returned to
node's home agent (the source of the tunnel) By the definition of the mobile node's home agent (the source of the tunnel). By the
IPv6 encapsulation [4], this encapsulating node MUST relay certain definition of IPv6 encapsulation [4], this encapsulating node MUST
ICMP error messages back to the original sender of the packet, which relay certain ICMP error messages back to the original sender of the
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
was sent), the router will encapsulate and tunnel the packet to the was sent), the router will encapsulate and tunnel the packet to the
mobile node's new care-of address (if it has a Binding Cache entry mobile node's new care-of address (if it has a Binding Cache entry
for the mobile node). As above, any ICMP error message caused by the for the mobile node). As above, any ICMP error message caused by the
packet while in this tunnel will be returned to the previous default packet while in this tunnel will be returned to the previous default
router (the source of the tunnel), which MUST relay certain ICMP router (the source of the tunnel), which MUST relay certain ICMP
error messages back to the correspondent node [4]. error messages back to the correspondent node [4].
Thus, in all cases, any meaningful ICMP error messages caused by Thus, in all cases, any meaningful ICMP error messages caused by
packets from a correspondent node to a mobile node will be returned packets from a correspondent node to a mobile node will be returned
to the correspondent node. If the correspondent node receives to the correspondent node. If the correspondent node receives
persistent ICMP Host Unreachable or Network Unreachable error persistent ICMP Host Unreachable or Network Unreachable error
messages after sending packets to a mobile node based on an entry in messages after sending packets to a mobile node based on an entry in
its Binding Cache, the correspondent node SHOULD delete this Binding its Binding Cache, the correspondent node SHOULD delete this Binding
Cache entry. If the correspondent node subsequently transmits Cache entry. If the correspondent node subsequently transmits
another packet to the mobile node, the packet will be routed to the another packet to the mobile node, the packet will be routed to the
mobile node's home subnet, intercepted by the mobile node's home mobile node's home subnet, intercepted by the mobile node's home
agent, and tunneled to the mobile node's care-of address using IPv6 agent, and tunneled to the mobile node's primary care-of address
encapsulation. The mobile node will then return a Binding Update to using IPv6 encapsulation. The mobile node will then return a Binding
the correspondent node, allowing it to recreate a (correct) Binding Update to the correspondent node, allowing it to recreate a (correct)
Cache entry for the mobile node. Binding Cache entry for the mobile node.
6.7. Sending Packets to a Mobile Node 6.8. Sending Packets to a Mobile Node
Before sending any packet, the sending node SHOULD examine its Before sending any packet, the sending node SHOULD examine its
Binding Cache for an entry for the destination address to which the Binding Cache for an entry for the destination address to which the
packet is being sent. If the sending node has a Binding Cache entry packet is being sent. If the sending node has a Binding Cache entry
for this address, the sending node SHOULD use a Routing header to for this address, the sending node SHOULD use a Routing header to
route the packet to this mobile node (the destination node) through route the packet to this mobile node (the destination node) by way
the care-of address recorded in that Binding Cache entry. For of the care-of address in the binding recorded in that Binding Cache
example, assuming use of a Type 0 Routing header [5], if no other use entry. For example, assuming use of a Type 0 Routing header [5], if
of a Routing header is involved in the routing of this packet, the no other use of a Routing header is involved in the routing of this
mobile node sets the following fields in the packet's IP header and packet, the mobile node sets the fields in the packet's IPv6 header
Routing header as indicated below: and Routing header as follows:
- The Destination Address in the packet's IP header is set to the - The Destination Address in the packet's IPv6 header is set to
mobile node's care-of address copied from the Binding Cache the mobile node's care-of address copied from the Binding Cache
entry. entry.
- The Routing header is initialized to contain a single route - The Routing header is initialized to contain a single route
segment, with an Address of the mobile node's home address (the segment, with an Address of the mobile node's home address (the
original destination address to which the packet was being sent). original destination address to which the packet was being sent).
Following the definition of a Type 0 Routing header [5], this packet Following the definition of a Type 0 Routing header [5], this packet
will routed to the mobile node's care-of address, where it will be will be routed to the mobile node's care-of address, where it will
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 IP - The mobile node swaps the Destination Address in the packet's
header and the Address specified in the Routing header. This IPv6 header and the Address specified in the Routing header.
results in the packet's IP Destination Address being set to the This results in the packet's IP Destination Address being set to
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. Since the mobile node recognizes its own
home address as one if its current IP addresses, the packet is home address as one if its current IP addresses, the packet is
processed further within the mobile node, in the same way then as processed further within the mobile node, in the same way then as
if the mobile node was at home. 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 7.3. The mobile node will then send address, as described in Section 7.4. The mobile node will then send
a Binding Update to the sending node, as described in Section 8.4, a Binding Update to the sending node, as described in Section 8.5,
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.
7. Home Agent Operation 7. Home Agent Operation
7.1. Primary Care-of Address Registration 7.1. Dynamic Home Agent Address Discovery
If a received Binding Update indicates that the mobile node sending
it is attempting dynamic home agent address discovery, as described
in Section 6.2, then the receiving node MUST process the Binding
Update as specified in this section.
A mobile node attempts dynamic home agent address discovery by
sending its "home registration" Binding Update to the Home-Agents
anycast address for its home IP subnet (the packet MUST also include
a Home Address option, as described in Section 8.4). A home agent
receiving such a Binding Update that is serving this subnet (the
home agent is configured with this anycast address on one of its
network interfaces) MUST reject the Binding Update and SHOULD return
a Binding Acknowledgement indicating this rejection and giving its
unicast address. The Status field in the Binding Acknowledgement
MUST be set to 135 (dynamic home agent address discovery response).
The mobile node, upon receiving this Binding Acknowledgement, MAY
then resend its Binding Update to the unicast home agent address
given in the Acknowledgement.
7.2. Primary Care-of Address Registration
General processing of a received Binding Update that requests a General processing of a received Binding Update that requests a
binding to be cached, is described in Section 6.2. However, if the binding to be cached, is described in Section 6.3. However, if the
Home Registration (H) bit is set in the Binding Update, then the Home Registration (H) bit is set in the Binding Update, then the
receiving node MUST process the Binding Update as specified in this receiving node MUST process the Binding Update as specified in this
section, rather than following the general procedure specified in section, rather than following the general procedure specified in
Section 6.2. Section 6.3.
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 message to the mobile SHOULD return a Binding Acknowledgement to the mobile node, in
node, in which the Status field is set to 132 (Home registration which the Status field is set to 132 (home registration not
not supported). supported).
- Else, if the home address for the binding in the Binding Update - Else, if the home address for the binding (the Home Address field
(the Source Address in the packet's IP header) is not an on-link in the packet's Home Address option) is not an on-link IPv6
IPv6 address with respect to the home agent's current Prefix address with respect to the home agent's current Prefix List,
List, then the home agent MUST reject the Binding Update and then the home agent MUST reject the Binding Update and SHOULD
SHOULD return a Binding Acknowledgement message to the mobile return a Binding Acknowledgement to the mobile node, in which the
node, in which the Status field is set to 133 (Not home subnet). Status field is set to 133 (not home subnet).
- 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 mobile node as a home agent), then the home agent SHOULD return a
a Binding Acknowledgement message to the mobile node, in which Binding Acknowledgement to the mobile node, in which the Status
the Status field is set to an appropriate value to indicate the field is set to an appropriate value to indicate the reason for
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 or
update the existing entry in its Binding Cache for this mobile node's update the existing entry in its Binding Cache for this mobile node's
home address, as described in Section 6.2. In addition, the home home address, as described in Section 6.3. In addition, the home
agent MUST mark this Binding Cache entry as a "home registration" agent MUST mark this Binding Cache entry as a "home registration"
to indicate that the node is serving as a home agent for this to indicate that the node is serving as a home agent for this
binding. Binding Cache entries marked as a "home registration" MUST binding. Binding Cache entries marked as a "home registration" MUST
be excluded from the normal cache replacement policy used for the be excluded from the normal cache replacement policy used for the
Binding Cache (Section 6.5) and MUST NOT be removed from the Binding Binding Cache (Section 6.6) and MUST NOT be removed from the Binding
Cache until the expiration of the Lifetime period. Cache until the expiration of the Lifetime period.
If the home agent was not already serving as a home agent for this If the home agent was not already serving as a home agent for this
mobile node (the home agent did not already have a Binding Cache mobile node (the home agent did not already have a Binding Cache
entry for this address marked as a "home registration"), then the entry for this home address marked as a "home registration"), then
home agent MUST multicast onto the home subnet (to the all-nodes the home agent MUST multicast onto the home subnet (to the all-nodes
multicast address) a Neighbor Advertisement message [8] on behalf multicast address) a Neighbor Advertisement message [9] on behalf
of the mobile node, to advertise the home agent's own link-layer of the mobile node, to advertise the home agent's own link-layer
address for the mobile node's home IP address. The Target Address in address for the mobile node's home IP address. The Target Address in
the Neighbor Advertisement message MUST be set to the mobile node's the Neighbor Advertisement message MUST be set to the mobile node's
home address, and the Advertisement MUST include a Target Link-layer home address, and the Advertisement MUST include a Target Link-layer
Address option specifying the home agent's link-layer address. The Address option specifying the home agent's link-layer address. The
Solicited Flag (S) in the Advertisement MUST NOT be set, since it was Solicited Flag (S) in the Advertisement MUST NOT be set, since it was
not solicited by any Neighbor Solicitation message. The Override not solicited by any Neighbor Solicitation message. The Override
Flag (O) in the Advertisement MUST be set, indicating that the Flag (O) in the Advertisement MUST be set, indicating that the
Advertisement SHOULD override any existing Neighbor Cache entry at Advertisement SHOULD override any existing Neighbor Cache entry at
any node receiving it. any node receiving it.
Any node on the home subnet receiving this Neighbor Advertisement Any node on the home subnet receiving this Neighbor Advertisement
message will thus update its Neighbor Cache to associate the mobile message will thus update its Neighbor Cache to associate the mobile
node's home address with the home agent's link layer address, causing node's home address with the home agent's link layer address, causing
it to transmit future packets for the mobile node instead to the it to transmit any future packets for the mobile node instead to
mobile node's home agent. Since multicasts on the local link (such the mobile node's home agent. Since multicasts on the local link
as Ethernet) are typically not guaranteed to be reliable, the home (such as Ethernet) are typically not guaranteed to be reliable, the
agent MAY retransmit this Neighbor Advertisement message up to home agent MAY retransmit this Neighbor Advertisement message up to
MAX_ADVERT_REXMIT times to increase its reliability. It is still MAX_ADVERT_REXMIT times to increase its reliability. It is still
possible that some nodes on the home subnet will not receive any of possible that some nodes on the home subnet will not receive any of
these Neighbor Advertisements, but these nodes will eventually be these Neighbor Advertisements, but these nodes will eventually be
able to detect the link-layer address change for the mobile node's able to detect the link-layer address change for the mobile node's
home address, through use of Neighbor Unreachability Detection [8]. home address, through use of Neighbor Unreachability Detection [9].
In addition, while this node is serving as a home agent to this In addition, while this node is serving as a home agent for this
mobile node (it still has a "home registration" entry for this mobile mobile node (it still has a "home registration" entry for this mobile
node in its Binding Cache), it MUST act as a proxy for this mobile node in its Binding Cache), it MUST act as a proxy for this mobile
node to reply to any received Neighbor Solicitation messages for it. node to reply to any received Neighbor Solicitation messages for
When a home agent receives a Neighbor Solicitation message, it MUST it. When a home agent receives a Neighbor Solicitation message, it
check if the Target Address specified in the message matches the home MUST check if the Target Address specified in the message matches
address of any mobile node for which it has a Binding Cache entry the home address of any mobile node for which it has a Binding Cache
marked as a "home registration". If such an entry exists in its entry marked as a "home registration". If such an entry exists
Binding Cache, the home agent MUST reply to the Neighbor Solicitation in its Binding Cache, the home agent MUST reply to the Neighbor
message with a Neighbor Advertisement message, giving the home Solicitation message with a Neighbor Advertisement message, giving
agent's own link-layer address as the link-layer address for the the home agent's own link-layer address as the link-layer address for
specified Target Address. Likewise, if the mobile node included its the specified Target Address. Likewise, if the mobile node included
home link-local address and set the Home Link-Local Address (L) bit its home link-local address and set the Home Link-Local Address
in its Binding Update with which it registered with its home agent, Present (L) bit in its Binding Update with which it established
its home agent MUST also similarly act as a proxy for the mobile this "home registration" with its home agent, its home agent MUST
node's home link-local address while it has a "home registration" also similarly act as a proxy for the mobile node's home link-local
entry in its Binding Cache for the mobile node. Acting as a proxy address while it has this "home registration" entry in its Binding
in this way allows other nodes on the mobile node's home subnet to Cache. Acting as a proxy in this way allows other nodes on the
resolve the mobile node's IPv6 home address and IPv6 link-local mobile node's home subnet to resolve the mobile node's IPv6 home
address, and allows the home agent to to defend these addresses on address and IPv6 link-local address, and allows the home agent to
the home subnet for Duplicate Address Detection [8]. to defend these addresses on the home subnet for Duplicate Address
Detection [9].
7.2. Primary Care-of Address De-registration 7.3. Primary Care-of Address De-registration
General processing of a received Binding Update that requests a General processing of a received Binding Update that requests a
binding to be deleted, is described in Section 6.3. However, if the binding to be deleted, is described in Section 6.4. However, if the
Home Registration (H) bit is set in the Binding Update, then the Home Registration (H) bit is set in the Binding Update, then the
receiving node MUST process the Binding Update as specified in this receiving node MUST process the Binding Update as specified in this
section, rather than following the general procedure specified in section, rather than following the general procedure specified in
Section 6.3. Section 6.4.
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 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 message to the mobile SHOULD return a Binding Acknowledgement to the mobile node, in
node, in which the Status field is set to 132 (Home registration which the Status field is set to 132 (home registration not
not supported). supported).
- Else, if the home address for the binding in the Binding Update - Else, if the home address for the binding (the Home Address
(the Source Address in the packet's IP header) is not an on-link field in the packet's Home Address option) is not an on-link
IPv6 address with respect to the home agent's current Prefix IPv6 address with respect to the home agent's current Prefix
List, then it MUST reject the Binding Update and SHOULD return a List, then it MUST reject the Binding Update and SHOULD return a
Binding Acknowledgement message to the mobile node, in which the Binding Acknowledgement to the mobile node, in which the Status
Status field is set to 133 (Not home subnet). 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.
In addition, the home agent MUST multicast a Neighbor Advertisement In addition, in this case, the home agent MUST multicast a Neighbor
message (to the all-nodes multicast address), giving the mobile Advertisement message (to the all-nodes multicast address), giving
node's home address as the Target Address, and specifying the mobile the mobile node's home address as the Target Address, and specifying
node's link-layer address in a Target Link-layer Address option in the mobile node's link-layer address in a Target Link-layer
the Neighbor Advertisement message. The home agent MAY retransmit Address option in the Neighbor Advertisement message. The home
this Neighbor Advertisement message up to MAX_ADVERT_REXMIT times agent MAY retransmit this Neighbor Advertisement message up to
to increase its reliability; any nodes on the home subnet that miss MAX_ADVERT_REXMIT times to increase its reliability; any nodes on the
all of these Neighbor Advertisements can also eventually detect the home subnet that miss all of these Neighbor Advertisements can also
link-layer address change for the mobile node's home address, through eventually detect the link-layer address change for the mobile node's
use of Neighbor Unreachability Detection [8]. home address, through use of Neighbor Unreachability Detection [9].
7.3. Tunneling Intercepted Packets to a Mobile Node 7.4. 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 packet, agent (for which the home agent is the original sender of the
the home agent is operating as a correspondent node of the mobile packet), the home agent is operating as a correspondent node of
node for this packet and the procedures described in Section 6.7 the mobile node for this packet and the procedures described in
apply. The home agent uses a Routing header to route the packet Section 6.8 apply. The home agent (as a correspondent node) uses a
to the mobile node through the care-of address in the home agent's Routing header to route the packet to the mobile node by way of the
Binding Cache (the mobile node's primary care-of address, in this care-of address in the home agent's Binding Cache (the mobile node's
case). primary care-of address, in this case).
In addition, while the mobile node is away from home and this node In addition, while the mobile node is away from home and this node
is acting as the mobile node's home agent, the home agent intercepts is acting as the mobile node's home agent, the home agent intercepts
any packets on the home subnet addressed to the mobile node's any packets on the home subnet addressed to the mobile node's
home address, as described in Section 7.1. The home agent cannot home address, as described in Section 7.2. The home agent cannot
use a Routing header to forward these intercepted packets to the use a Routing header to forward these intercepted packets to the
mobile node, since it cannot modify the packet in flight without mobile node, since it cannot modify the packet in flight without
invalidating any existing IPv6 Authentication header present in the invalidating any existing IPv6 Authentication header present in the
packet [1]. packet [1].
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 mobile node itself (using its
primary care-of address as registered with the home agent). When a primary care-of address as registered with the home agent). When a
home agent encapsulates an intercepted packet for forwarding to the home agent encapsulates an intercepted packet for forwarding to the
mobile node, the home agent sets the Source Address in the prepended mobile node, the home agent sets the Source Address in the prepended
tunnel IP header to its own IP address, and sets the Destination tunnel IP header to the home agent's own IP address, and sets the
Address in the tunnel IP header to the mobile node's primary care-of Destination Address in the tunnel IP header to the mobile node's
address. When received by the mobile node (using its primary care-of primary care-of address. When received by the mobile node (using its
address), normal processing of the tunnel header [4] will result in primary care-of address), normal processing of the tunnel header [4]
decapsulation and processing of the original packet by the mobile will result in decapsulation and processing of the original packet by
node. the mobile node.
7.4. Renumbering the Home Subnet 7.5. Renumbering the Home Subnet
Neighbor Discovery [8] specifies a mechanism by which all nodes on a Neighbor Discovery [9] specifies a mechanism by which all nodes on a
subnet can gracefully autoconfigure new addresses, say by each node subnet can gracefully autoconfigure new addresses, say by each node
combining a new routing prefix with its existing link-layer address. combining a new routing prefix with its existing link-layer address.
As currently specified, this mechanism works when the nodes are on As currently specified, this mechanism works when the nodes are on
the same link as the router issuing the necessary multicast packets the same link as the router issuing the necessary multicast packets
to advertise the new routing prefix(es) appropriate for the link. to advertise the new routing prefix(es) appropriate for the link.
However, for mobile nodes away from home, special care must be taken However, for mobile nodes away from home, special care must be taken
to allow the mobile nodes to renumber gracefully. The most direct to allow the mobile nodes to renumber gracefully. The most direct
method of ensuring this is for the home agent to encapsulate and method of ensuring this is for the home agent to encapsulate and
tunnel the multicast packets to the primary care-of address of each 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 mobile node for which it is serving as the home agent. The rules for
this are as follows: this are as follows:
- A mobile node assumes that its routing prefix has not changed - A mobile node assumes that its routing prefix has not changed
unless it receives authenticated Router Advertisement messages unless it receives an authenticated Router Advertisement message
from its home agent that the prefix has changed. from its home agent that the prefix has changed.
- When the mobile node is at home, the home agent does not tunnel - When the mobile node is at home, the home agent does not tunnel
Router Advertisements to it. Router Advertisements to it.
- The mobile node's home agent serves as a proxy for the mobile - The mobile node's home agent serves as a proxy for the mobile
node's home address and link-local address, including defending node's home address and link-local address, including defending
these addresses for Duplicate Address Detection, while the mobile these addresses for Duplicate Address Detection, while the mobile
node is registered with the home agent away from home. node is registered with the home agent away from home.
- When a home subnet prefix changes, the home agent tunnels Router - When a home subnet prefix changes, the home agent tunnels Router
Advertisement packets to each mobile node which is currently Advertisement packets to each mobile node registered with it that
away from home and using a home address with the affected is currently away from home and using a home address with the
routing prefix. Such tunneled Router Advertisements MUST be affected routing prefix. Such tunneled Router Advertisements
authenticated [1]. MUST be authenticated [1].
- When a mobile node receives a tunneled Router Advertisement - When a mobile node receives a tunneled Router Advertisement
containing a new routing prefix, it must perform the standard containing a new routing prefix, it MUST perform the standard
autoconfiguration operation to create its new address autoconfiguration operation to create its new address.
- When a mobile node returns to its home subnet, it must again - When a mobile node returns to its home subnet, it must again
perform Duplicate Address Detection at the earliest possible perform Duplicate Address Detection at the earliest possible
moment after it has registered with its home agent. 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 - A mobile node MAY send a Router Solicitation to its home agent at
any time, within the constraints imposed by rate control in the any time, within the constraints imposed by rate control defined
Neighbor Discovery specification [8] by Neighbor Discovery [9].
8. Mobile Node Operation 8. Mobile Node Operation
8.1. Movement Detection 8.1. Sending Packets While Away from 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
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
packet, as follows:
- For most packets, the mobile node will generally use its home
address as the source of the packet. Doing so makes its mobility
and the fact that it is currently away from home transparent to
the correspondent nodes with which it communicates. For packets
sent that are part of transport-level connections established
while the mobile node was at home, the mobile node MUST use
its home address. Likewise, for packets sent that are part of
transport-level connections that the mobile node may still be
using after moving to a new location, the mobile node SHOULD use
its home address.
- For short-term communication, particularly for communication
that may easily be retried if it fails, the mobile node MAY
choose to use one of its care-of addresses as the source of the
packet. An example of this type of communication might be DNS
queries sent by the mobile node [7, 8]. Using the mobile node's
care-of address as the source for such queries will generally
have a lower overhead than using the mobile node's home address,
since no extra options need be used in either the query or its
reply, and all packets can be routed normally, directly between
their source and destination without relying on Mobile IP. If the
mobile node has no particular knowledge that the communication
being sent fits within this type of communication, however, the
mobile node SHOULD use its home address.
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
is required for sending this packet. The packet is simply addressed
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
address.
On the other hand, if the mobile node uses its home address as the
source of a packet while away from home, the mobile node SHOULD
construct the packet as follows:
- The Source Address field in the packet's IPv6 header is set to
one of the mobile node's care-of addresses.
- A Home Address option is included in the packet, with the Home
Address field set to the mobile node's home address.
Without this use of the care-of address in the IPv6 header, with the
mobile node's home address instead in the Home Address option, the
packet will likely be discarded by any router implementing ingress
filtering [6].
8.2. Movement Detection
A mobile node MAY use any combination of mechanisms available to A mobile node MAY use any combination of mechanisms available to
it to detect when its link-level point of attachment has moved it to detect when its link-level point of attachment has moved
from one IP subnet to another. The primary movement detection from one IP subnet to another. The primary movement detection
mechanism for Mobile IPv6 defined here uses the facilities of mechanism for Mobile IPv6 defined here uses the facilities of
IPv6 Neighbor Discovery, including Router Discovery and Neighbor IPv6 Neighbor Discovery, including Router Discovery and Neighbor
Unreachability Detection. The description here is based on the Unreachability Detection. The description here is based on the
conceptual model of the organization and data structures defined by conceptual model of the organization and data structures defined by
Neighbor Discovery [8]. Neighbor Discovery [9].
Mobile nodes SHOULD use Router Discovery to discover new routers and Mobile nodes SHOULD use Router Discovery to discover new routers and
on-link network prefixes; a mobile node MAY send Router Solicitation on-link network prefixes; a mobile node MAY send Router Solicitation
messages, or MAY wait for unsolicited (periodic) Router Advertisement messages, or MAY wait for unsolicited (periodic) Router Advertisement
messages, as specified for Router Discovery [8]. Based on received messages, as specified for Router Discovery [9]. Based on received
Router Advertisement messages, a mobile node (in the same way as any Router Advertisement messages, a mobile node (in the same way as any
other node) maintains an entry in its Default Router List for each other node) maintains an entry in its Default Router List for each
router, and an entry in its Prefix List for each network prefix, that router, and an entry in its Prefix List for each network prefix, that
it currently considers to be on-link. Each entry in these lists has it currently considers to be on-link. Each entry in these lists has
an associated invalidation timer value (extracted from the Router an associated invalidation timer value (extracted from the Router
Advertisement) used to expire the entry when it becomes invalid. Advertisement) used to expire the entry when it becomes invalid.
While away from home, a mobile node SHOULD select one router from its While away from home, a mobile node SHOULD select one router from its
Default Router List to use as its default router, and one network Default Router List to use as its default router, and one network
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 network prefix in its primary care-of address. A mobile node the network 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
network prefixes from its Prefix List. The method by which a mobile network prefixes from its Prefix List. The method by which a mobile
node selects and forms a care-of address from the available network node selects and forms a care-of address from the available network
prefixes is described in Section 8.2. The mobile node registers prefixes is described in Section 8.3. 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 8.3. Section 8.4.
While away from home and using some router as its default router, While a mobile node is away from home and using some router as its
it is important for a mobile node to be able to quickly detect when default router, it is important for the mobile node to be able to
that router becomes unreachable, so that it can switch to a new quickly detect when that router becomes unreachable, so that it can
default router and to a new primary care-of address. Since some switch to a new default router and to a new primary care-of address.
links (notably wireless) do not necessarily work equally well in both Since some links (notably wireless) do not necessarily work equally
directions, it is likewise important for the mobile node to detect well in both directions, it is likewise important for the mobile
when it becomes unreachable to its default router, so that the mobile node to detect when it becomes unreachable to packets sent from its
node can take steps to ensure that any correspondent nodes attempting default router, so that the mobile node can take steps to ensure that
to communicate with the it can still reach it through some other any correspondent nodes attempting to communicate with the it can
route. still 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 [8], while the mobile node is actively sending Neighbor Discovery [9], 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 is still reachable either through indications detect that the router is still reachable either through indications
from upper layer protocols on the mobile node that a connection is from upper layer protocols on the mobile node that a connection is
making "forward progress" (e.g., receipt of TCP acknowledgements for making "forward progress" (e.g., receipt of TCP acknowledgements for
new data transmitted), or through receipt of a Neighbor Advertisement new data transmitted), or through receipt of a Neighbor Advertisement
message form its default router in response to an explicit Neighbor message form its default router in response to an explicit Neighbor
Solicitation messages to it. Note that although this mechanism only Solicitation messages to it. Note that although this mechanism only
detects that the mobile node's default router has become unreachable detects that the mobile node's default router has become unreachable
to the mobile node while the mobile node is actively sending packets to the mobile node while the mobile node is actively sending packets
to it, this is the only time that this direction of reachability to it, this is the only time that this direction of reachability
skipping to change at page 32, line 32 skipping to change at page 39, line 39
continually probe its default router with Neighbor Solicitation continually probe its default router with Neighbor Solicitation
messages even when it is not otherwise actively sending packets to messages even when it is not otherwise actively sending packets to
it. Instead, a mobile node SHOULD consider receipt of any IPv6 it. Instead, a mobile node SHOULD consider receipt of any IPv6
packets from its current default router as an indication that it is packets from its current default router as an indication that it is
still reachable from the router. Both packets from the router's IP still reachable from the router. Both packets from the router's IP
address and (IPv6) packets from its link-layer address (e.g., those address and (IPv6) packets from its link-layer address (e.g., those
forwarded but not originated by the router) SHOULD be considered. forwarded but not originated by the router) SHOULD be considered.
Since the router SHOULD be sending periodic multicast Router Since the router SHOULD be sending periodic multicast Router
Advertisement messages, the mobile node will have frequent Advertisement messages, the mobile node will have frequent
opportunity to check if it is still reachable to its default router, opportunity to check if it is still reachable from its default
even in the absence of other packets to it from the router. On some router, even in the absence of other packets to it from the router.
types of network interfaces, the mobile node MAY also supplement this On some types of network interfaces, the mobile node MAY also
by setting its network interface into "promiscuous" receive mode, supplement this by setting its network interface into "promiscuous"
so that it is able to receive all packets on the link, including receive mode, so that it is able to receive all packets on the link,
those not link-level addressed to it. The mobile node will then including those not link-level addressed to it. The mobile node will
be able to detect any packets sent by the router, in order to to then be able to detect any packets sent by the router, in order to to
detect reachability from the router. This may be useful on very low detect reachability from the router. This may be useful on very low
bandwidth (e.g., wireless) links, but its use MUST be configurable on bandwidth (e.g., wireless) links, but its use MUST be configurable on
the mobile node. 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 still reachable from its current default router (i.e., the is still reachable from its current default router (i.e., the
mobile node receives no packets form the router for a period of mobile node receives no packets from the router for a period of
time), then the mobile node SHOULD actively probe the router with time), then the mobile node SHOULD 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.
skipping to change at page 33, line 34 skipping to change at page 40, line 41
mobile node is reachable. For example, a mobile node MAY use signal mobile node is reachable. For example, a mobile node MAY use signal
strength or signal quality information (with suitable hysteresis) strength or signal quality information (with suitable hysteresis)
for its link with the available default routers to decide when to for its link with the available default routers to decide when to
switch to a new primary care-of address using that default router switch to a new primary care-of address using that default router
rather than its current default router (and current primary care-of rather than its current default router (and current primary care-of
address). Even though the mobile node's current default router may address). Even though the mobile node's current default router may
still be reachable in terms of Neighbor Unreachability Detection, the still be reachable in terms of Neighbor Unreachability Detection, the
mobile node MAY use such lower-layer information to determine that mobile node MAY use such lower-layer information to determine that
switching to a new default router would provide a better connection. switching to a new default router would provide a better connection.
8.2. Forming New Care-of Addresses 8.3. Forming New Care-of Addresses
After detecting that its link-layer point of attachment has moved After detecting that its link-layer point of attachment has moved
from one IPv6 subnet to another (i.e., its current default router from one IPv6 subnet to another (i.e., its current default router
has become unreachable and it has discovered a new default router), has become unreachable and it has discovered a new default router),
a mobile node SHOULD form a new primary care-of address using one of a mobile node SHOULD form a new primary care-of address using one of
the on-link network prefixes advertised by the new router. A mobile the on-link network prefixes advertised by the new router. A mobile
node MAY form a new primary care-of address at any time, except node MAY form a new primary care-of address at any time, except
that it MUST NOT do so too frequently (not more often than once per that it MUST NOT do so too frequently (not more often than once per
MAX_UPDATE_RATE seconds). MAX_UPDATE_RATE seconds).
In addition, after discovering a new on-link network prefix, a In addition, after discovering a new on-link network prefix, a
mobile node MAY form a new (non-primary) care-of address using that mobile node MAY form a new (non-primary) care-of address using that
network prefix, even when it has not switched to a new default network prefix, even when it has not switched to a new default
router. A mobile node can have only one primary care-of address router. A mobile node can have only one primary care-of address at
at a time (registered with its home agent), but it MAY have an a time (which is registered with its home agent), but it MAY have an
additional care-of address for each network prefix on its current additional care-of address for any or all of the network prefixes on
link. Furthermore, since a wireless network interface may actually its current link. Furthermore, since a wireless network interface
allow a mobile node to be reachable on more than one link at a time may actually allow a mobile node to be reachable on more than one
(i.e., within wireless transmitter range of routers on more than one link at a time (i.e., within wireless transmitter range of routers
separate link), a mobile node MAY have care-of addresses on more than on more than one separate link), a mobile node MAY have care-of
one link at a time. The use of more than one care-of address at a addresses on more than one link at a time. The use of more than one
time is described in Section 8.9. care-of address at a time is described in Section 8.10.
As described in Section 3, in order to form a new care-of address, As described in Section 3.1, in order to form a new care-of address,
a mobile node MAY use either stateless [14] or stateful (e.g., a mobile node MAY use either stateless [16] or stateful (e.g.,
DHCPv6 [3]) address autoconfiguration. If a mobile node needs to DHCPv6 [3]) 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 IP 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 visiting address that has been assigned to it for its use only while visiting
a specific foreign subnet. For example, a mobile node may be a specific foreign subnet. 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 subnet, for its use while visiting that administrator of some foreign subnet, for its use while visiting that
subnet. If so, rather than using address autoconfiguration to form subnet. If so, rather than using address autoconfiguration to form
a new care-of address using this network prefix, the mobile node a new care-of address using this network prefix, the mobile node
SHOULD use its own pre-assigned address as its care-of address on MAY use its own pre-assigned address as its care-of address on this
this subnet. subnet.
8.3. Sending Binding Updates to the Home Agent 8.4. 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 8.1 and 8.2, a mobile node MUST register this care-of in Sections 8.2 and 8.3, 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 Home Registration (H) containing a Binding Update option, with the packet constructed as
bit is set in the Binding Update. The mobile node also sets the follows:
Acknowledge (A) bit in the Binding Update, requesting the home
agent to return a Binding Acknowledgement message in response to - The Home Registration (H) bit MUST be set in the Binding Update.
this Binding Update. As described in Section 4.2, the mobile node
SHOULD retransmit this Binding Update to its home agent until it - The Acknowledge (A) bit MUST be set in the Binding Update.
receives a matching Binding Acknowledgement message. Once reaching a
retransmission timeout period of MAX_BINDACK_TIMEOUT, the mobile node - The packet MUST contain a Home Address option, giving the mobile
SHOULD continue to periodically retransmit the Binding Update at this node's home address for the binding.
rate until acknowledged (or until it begins attempting to register a
- The care-of address for the binding MUST be used as the Source
Address in the packet's IPv6 header, or the Care-of Address
Present (C) bit MUST be set in the Binding Update and the care-of
address for binding MUST be specified in the Care-of Address
field in the Binding Update.
The Acknowledge (A) bit in the Binding Update requests the home
agent to return a Binding Acknowledgement in response to this
Binding Update. As described in Section 4.2, the mobile node SHOULD
retransmit this Binding Update to its home agent until it receives
a matching Binding Acknowledgement. Once reaching a retransmission
timeout period of MAX_BINDACK_TIMEOUT, the mobile node SHOULD
continue to periodically retransmit the Binding Update at this rate
until acknowledged (or until it begins attempting to register a
different primary care-of address). different primary care-of address).
8.4. Sending Binding Updates to Correspondent Nodes It is possible that when the mobile node needs to send such a Binding
Update to its home agent, that the mobile node does not know the
address of any router in its home subnet that can serve as a home
agent for it. In this case, the mobile node SHOULD use the dynamic
home agent address resolution procedure to find the address of a
suitable home agent in its home subnet. To do so, the mobile node
sends the packet, as described above, with the Destination Address in
the packet's IPv6 header set the Home-Agents anycast address for its
home subnet. The home agent in its home subnet that receives this
Binding Update will reject the Update, returning to the mobile node
the home agent's unicast IP address. The mobile node SHOULD then
retransmit its Binding Update to this home agent using the provided
unicast address.
If the mobile node has a current registration with some home agent
in its home subnet (the Lifetime for that registration has not yet
expired), then the mobile node MUST attempt any new registration
first with that home agent. If that registration attempt fails
(e.g., times out or is rejected), the mobile node SHOULD then
reattempt this registration with another home agent in its home
subnet. If the mobile node knows of no other suitable home agent,
then it MAY attempt the dynamic home agent address resolution
procedure described above.
8.5. 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 (subject to the rate limiting defined in Section 8.7). In any time to allow it to cache its current care-of address (subject
any Binding Update sent by a mobile node, the Care-of Address field to the rate limiting defined in Section 8.8). In any Binding Update
MUST be set to one of the care-of addresses currently in use by the sent by a mobile node, the care-of address (either the Source Address
mobile node or to the mobile node's home address. If set to one of in the packet's IPv6 header or the Care-of Address field in the
the mobile node's current care-of addresses (the care-of address Binding Update) MUST be set to one of the care-of addresses currently
given MAY differ from the mobile node's primary care-of address), the in use by the mobile node or to the mobile node's home address.
Binding Update requests the correspondent node to create or update If set to one of the mobile node's current care-of addresses (the
a an entry for the mobile node in the correspondent node's Binding care-of address given MAY differ from the mobile node's primary
Cache to record this care-of address for use in sending future care-of address), the Binding Update requests the correspondent node
packets to the mobile node. If, instead, the Care-of Address field to create or update an entry for the mobile node in the correspondent
is set to the mobile node's home address, the Binding Update requests node's Binding Cache to record this care-of address for use in
the correspondent node to delete any existing Binding Cache entry sending future packets to the mobile node. If, instead, the care-of
that it has for the mobile node. A mobile node MAY set the Care-of address is set to the mobile node's home address, the Binding Update
Address field differently for sending Binding Updates to different 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. 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 of 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 has not yet expired. When sending a Binding Update, if an binding has not yet expired. 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 is updated to reflect the new Binding existing Binding Update List entry is updated to reflect the new
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 8.3), the mobile node will also typically send a Binding Section 8.4), the mobile node will also send a Binding Update to each
Update to each correspondent node for which an entry exists in the correspondent node for which an entry exists in the mobile node's
mobile node's Binding Update List. Thus, correspondent nodes are Binding Update List. Thus, correspondent nodes are generally kept
generally kept updated and can send almost all packets directly to updated about the mobile node's binding and can send packets directly
the mobile node using the mobile node's current binding. to the mobile node using the mobile node's current care-of 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 no
Binding Cache entry for the mobile node, or for which the mobile node Binding Cache entry for the mobile node, or for which the mobile node
can deduce that the original sender of the packet has an out-of-date can deduce that the original sender of the packet has an out-of-date
care-of address in its Binding Cache entry for the mobile node, the care-of address for the mobile node in its Binding Cache, the mobile
mobile node SHOULD return a Binding Update to the sender giving its node SHOULD return a Binding Update to the sender giving its current
current care-of address. In particular, the mobile node SHOULD care-of address. In particular, the mobile node SHOULD return a
return a Binding Update in response to receiving a packet that meets Binding Update in response to receiving a packet that meets all of
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) IP header is equal - The Destination Address in the tunnel (outer) IPv6 header is
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) IP header is - The Destination Address in the original (inner) IPv6 header is
equal to the mobile node's home address. If the original packet equal to the mobile node's home address. If the original packet
contains a Routing header, the final Address indicated in the contains a Routing header, the final Address indicated in the
Routing header should be used in this comparison rather than the Routing header should be used in this comparison rather than the
Destination Address in the original IP header. Destination Address in the original IPv6 header.
- The Source Address in the tunnel (outer) IP header differs from - The Source Address in the tunnel (outer) IPv6 header differs from
the Source Address in the original (inner) IP 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 in
response to receiving a packet meeting all of the tests above, is the response to receiving a packet meeting all of the tests above, is the
Source Address in the original (inner) IP header of the packet. Source Address in the original (inner) IPv6 header of the 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 to be
sure that its new care-of address has been added to a correspondent sure that its new care-of address has been added to a correspondent
node's Binding Cache, the mobile node MAY request an acknowledgement node's Binding Cache, the mobile node MAY request an acknowledgement
by setting the Acknowledge (A) bit in the Binding Update. In this by setting the Acknowledge (A) bit in the Binding Update. In this
case, however, the mobile node SHOULD NOT continue to retransmit the case, however, the mobile node SHOULD NOT continue to retransmit the
Binding Update once the retransmission timeout period has reached Binding Update once the retransmission timeout period has reached
MAX_BINDACK_TIMEOUT. 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 4.1. No other IPv6 nodes are authorized to send Binding Section 4.1. No other IPv6 nodes are authorized to send Binding
Updates on behalf of a mobile node. Updates on behalf of a mobile node.
8.5. Sending Binding Updates to the Previous Default Router 8.6. Sending Binding Updates to the Previous Default Router
After switching to a new default router (and thus also changing After switching to a new default router (and thus also changing its
its primary care-of address), a mobile node SHOULD send a Binding primary care-of address), a mobile node SHOULD send a Binding Update
Update message to its previous default router, giving its new care-of to its previous default router, giving its new care-of address. If
address. If the mobile node sends such a Binding Update, the Source the mobile node sends such a Binding Update, the home address for
Address in the packet carrying this Binding Update MUST be set the the binding, specified in the Home Address option included in the
mobile node's old primary care-of address (that it used while using packet carrying this Binding Update, MUST be set the mobile node's
this default router), and the Care-of Address field MUST be set to old primary care-of address (that it used while using this default
the mobile node's new primary care-of address. In addition, the Home router), and the care-of address for the binding (either the Source
Registration (H) bit MUST also be set in this Binding Update, to Address in the packet's IPv6 header or the Care-of Address field in
request the mobile node's previous default router to temporarily act the Binding Update) MUST be set to the mobile node's new primary
as a home agent for the mobile node's old primary care-of address. care-of address. In addition, the Home Registration (H) bit MUST
Note that the previous router does not necessarily know the mobile also be set in this Binding Update, to request the mobile node's
node's home address as part of this sequence of events. previous default router to temporarily act as a home agent for the
mobile node's old primary care-of address. Note that the previous
router does not necessarily know the mobile node's (permanent) home
address as part of this registration.
If any subsequent packets arrive at this previous router for If any subsequent packets arrive at this previous router for
forwarding to the mobile node's old primary care-of address, forwarding to the mobile node's old primary care-of address,
the router SHOULD encapsulate each such packet (using IPv6 the router SHOULD encapsulate each such packet (using IPv6
encapsulation [4]) and tunnel it to the mobile node at its new encapsulation [4]) and tunnel it to the mobile node at its new
primary care-of address. Moreover, for the lifetime of the "home primary care-of address. Moreover, for the lifetime of the "home
registration" Binding Cache entry at this router, this router MUST registration" Binding Cache entry for the mobile node at this
act as a proxy for the mobile node's previous care-of address, router, this router MUST act as a proxy for the mobile node's
for purposes of participation in Neighbor Discovery [8], in the previous care-of address, for purposes of participation in Neighbor
same way as any home agent does for a mobile node's home address Discovery [9], in the same way as any home agent does for a mobile
(Section 7.1). This allows the router to intercept packets addressed node's home address (Section 7.2). This allows the router to
to the mobile node's previous care-of address, and to encapsulate and intercept packets addressed to the mobile node's previous care-of
tunnel them to the mobile node's new care-of address, as described in address, and to encapsulate and tunnel them to the mobile node's new
Section 7.3. care-of address, as described in Section 7.4.
8.6. Retransmitting Binding Updates 8.7. Retransmitting Binding Updates
If, after sending a Binding Update in which the Acknowledge (A) If, after sending a Binding Update in which the Acknowledge (A) bit
bit is set, a mobile node fails to receive an acceptable Binding is set, a mobile node fails to receive a Binding Acknowledgement
Acknowledgement within INITIAL_BINDACK_TIMEOUT seconds, the within INITIAL_BINDACK_TIMEOUT seconds, the mobile node SHOULD
mobile node SHOULD retransmit the Binding Update until a Binding retransmit the Binding Update until a Binding Acknowledgement
Acknowledgement is received. Such a retransmitted Binding is received. Such a retransmitted Binding Update MUST use he
Update MUST use he same Identification value as the original same Sequence Number value as the original transmission. The
transmission. The retransmissions by the mobile node MUST use retransmissions by the mobile node MUST use an exponential
an exponential back-off process, in which timeout period is back-off process, in which the timeout period is doubled
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.
8.7. Rate Limiting for Sending Binding Updates 8.8. 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 correspondent node. After sending 5 MAX_UPDATE_RATE seconds to any node. After sending MAX_FAST_UPDATES
consecutive Binding Updates to a particular correspondent node with consecutive Binding Updates to a particular node with the same
the same care-of address, the mobile node SHOULD reduce its rate care-of address, the mobile node SHOULD reduce its rate of sending
of sending Binding Updates to that correspondent node, to the rate Binding Updates to that node, to the rate of SLOW_UPDATE_RATE per
of SLOW_UPDATE_RATE per second. The mobile node MAY continue to second. The mobile node MAY continue to send Binding Updates at the
send Binding Updates at the slower rate indefinitely, in hopes that slower rate indefinitely, in hopes that the node will eventually
the correspondent node will eventually be able to process a Binding be able to process a Binding Update and begin to route its packets
Update and begin to route its packets directly to the mobile node at directly to the mobile node at its new care-of address.
its new care-of address.
8.8. Receiving Binding Acknowledgements 8.9. 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 an IP Authentication header and the - The packet contains an IP Authentication header and the
authentication is valid [1]. The Authentication header is authentication is valid [1]. The Authentication header MUST
assumed to provide both authentication and integrity protection. provide both sender authentication, integrity protection, and
replay 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
8 octets. 9 octets.
- The Identification field is valid. - The Sequence Number field matches the Sequence Number sent by the
mobile node to this destination address in an outstanding Binding
Update.
Any Binding Acknowledgement not satisfying all of these tests MUST be Any Binding Acknowledgement not satisfying all of these tests MUST be
silently ignored, although the remainder of the packet (i.e., other silently ignored, although the remainder of the packet (i.e., other
options, extension headers, or payload) SHOULD be processed normally options, extension headers, or payload) SHOULD be processed normally
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 thus stop retransmitting the Binding Update.
- If the Status field indicates that the Binding Update was not - If the Status field indicates that the Binding Update was not
accepted (the Status field is greater than or equal to 128), then accepted (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. Optionally, the mobile node MAY take steps to correct the entry (and MUST also stop retransmitting the Binding Update).
cause of the error and retransmit the Binding Update, subject to Optionally, the mobile node MAY then take steps to correct the
the rate limiting restriction specified in Section 8.7. cause of the error and retransmit the Binding Update (with a new
Sequence Number value), subject to the rate limiting restriction
specified in Section 8.8.
8.9. Using Multiple Care-of Addresses 8.10. Using Multiple Care-of Addresses
As described in Section 8.2, a mobile node MAY have more than As described in Section 8.3, a mobile node MAY have more than one
one care-of address at a time. Particularly in the case of many care-of address at a time. Particularly in the case of many wireless
wireless networks, a mobile node effectively may be reachable networks, a mobile node effectively might be reachable through
through multiple link-level points of attachment at the same time multiple link-level points of attachment at the same time (e.g.,
(e.g., with overlapping wireless cells), on which different on-link with overlapping wireless cells), on which different on-link network
network prefixes may exist. A mobile node SHOULD select a primary prefixes may exist. A mobile node SHOULD select a primary care-of
care-of address from among those care-of addresses it has formed address from among those care-of addresses it has formed using any
using any of these network prefixes, based on the movement detection of these network prefixes, based on the movement detection mechanism
mechanism in use (Section 8.1). When the mobile node selects a new in use, as described in Section 8.2. When the mobile node selects
primary care-of address, it MUST register it with its home agent a new primary care-of address, it MUST register it with its home
through a Binding Update message with the Home Registration (H) and agent through a Binding Update with the Home Registration (H) and
Acknowledge (A) bits set, as described in Section 8.3. Acknowledge (A) bits set, as described in Section 8.4.
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 connected to that link. If the previous primary care-of address
was allocated using stateful address autoconfiguration [3], the was allocated using stateful address autoconfiguration [3], the
mobile node may not wish to release the address immediately upon mobile node may not wish to release the address immediately upon
switching to a new primary care-of address. The stateful address switching to a new primary care-of address. The stateful address
autoconfiguration server will allow mobile nodes to acquire new autoconfiguration server will allow mobile nodes to acquire new
addresses while still using previously allocated addresses. addresses while still using previously allocated addresses.
8.10. Returning Home 8.11. Returning Home
A mobile node detects that it has returned to its home subnet through A mobile node detects that it has returned to its home subnet through
the movement detection algorithm in use (Section 8.1), when the the movement detection algorithm in use (Section 8.2), when the
mobile node detects that the network prefix of its home subnet is mobile node detects that the network prefix of its home subnet is
again on-link. The mobile node SHOULD then send a Binding Update to again on-link. The mobile node SHOULD then send a Binding Update to
its home agent, to instruct its home agent to no longer intercept its home agent, to instruct its home agent to no longer intercept
or tunnel packets for it. In this Binding Update, the mobile node or tunnel packets for it. In this Binding Update, the mobile node
MUST set the Care-of Address field to its own IPv6 home address. As MUST set the care-of address for the binding (Source Address field in
the packet's IPv6 header) to the mobile node's own home address. As
with other Binding Updates sent to register with its home agent, the with other Binding Updates sent to register with its home agent, the
mobile node MUST set the Acknowledge (A) and Home Registration (H) mobile node MUST set the Acknowledge (A) and Home Registration (H)
bits, and SHOULD retransmit the Binding Update until a matching bits, and SHOULD retransmit the Binding Update until a matching
Binding Acknowledgement message is received. Binding Acknowledgement is received.
In addition, the mobile node MUST multicast onto the home subnet In addition, the mobile node MUST multicast onto the home subnet
(to the all-nodes multicast address) a Neighbor Advertisement (to the all-nodes multicast address) a Neighbor Advertisement
message [8], to advertise its link-layer address for its own IPv6 message [9], to advertise the mobile node's own link-layer address
home address. The Target Address in this Neighbor Advertisement for its own home address. The Target Address in this Neighbor
message MUST be set to the mobile node's home address, and the Advertisement message MUST be set to the mobile node's home address,
Advertisement MUST include a Target Link-layer Address option and the Advertisement MUST include a Target Link-layer Address
specifying the mobile node's link-layer address. Similarly, the option specifying the mobile node's link-layer address. Similarly,
mobile node MUST multicast a Neighbor Advertisement message to the mobile node MUST multicast a Neighbor Advertisement message to
advertise its link-layer address for its IPv6 link-local address. advertise its link-layer address for its IPv6 link-local address.
The Solicited Flag (S) in these Advertisements MUST NOT be set, since The Solicited Flag (S) in these Advertisements MUST NOT be set, since
they were not solicited by any Neighbor Solicitation message. The they were not solicited by any Neighbor Solicitation message. The
Override Flag (O) in these Advertisements MUST be set, indicating Override Flag (O) in these Advertisements MUST be set, indicating
that the Advertisements SHOULD override any existing Neighbor Cache that the Advertisements SHOULD override any existing Neighbor Cache
entries at any node receiving them. entries at 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 not guaranteed to be reliable, the mobile node MAY retransmit
these Neighbor Advertisement messages up to MAX_ADVERT_REXMIT times these Neighbor Advertisement messages up to MAX_ADVERT_REXMIT times
to increase their reliability. It is still possible that some to increase their reliability. It is still possible that some
nodes on the home subnet will not receive any of these Neighbor nodes on the home subnet will not receive any of these Neighbor
Advertisements, but these nodes will eventually be able to recover Advertisements, but these nodes will eventually be able to recover
through use of Neighbor Unreachability Detection [8]. through use of Neighbor Unreachability Detection [9].
9. Routing Multicast Packets 9. Routing Multicast Packets
A mobile node that is connected to its home subnet functions in the A mobile node that is connected to its home subnet 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 subnet. node that is not on its home subnet.
In order receive packets sent to some multicast group, a mobile node In order receive packets sent to some multicast group, a mobile node
must join the that multicast group. One method by which a mobile must join the 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 subnet being visited. This option assumes that there is a foreign subnet being visited. This option assumes that there is a
multicast router present on the foreign subnet. The mobile node multicast router present on the foreign subnet. The mobile node
SHOULD use its care-of address sharing a network prefix with the SHOULD use its care-of address sharing a network prefix with the
multicast router, as the source IPv6 address of its multicast group multicast router, as the source IPv6 address of its multicast group
membership control message packets. membership control 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, assuming that its home agent bi-directional tunnel to its home agent, assuming that its home agent
is a multicast router. The mobile node tunnels the appropriate is a multicast router. The mobile node tunnels the appropriate
multicast group membership control packets to its home agent, and the multicast group membership control packets to its home agent, and the
home agent forwards multicast packets down the tunnel to the mobile home agent forwards multicast packets down the tunnel to the mobile
node. The home agent MUST tunnel the packet directly to the mobile node.
node's primary care-of address.
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 subnet also has two options: (1) send directly on the foreign subnet
being visited; or (2) send via a tunnel to its home agent. Because being visited; or (2) send via a tunnel to its home agent. Because
multicast routing in general depends upon the Source Address used multicast routing in general depends upon the Source Address used
in the IP header of the multicast packet, a mobile node that sends in the IPv6 header of the multicast packet, a mobile node that
multicast packets directly on the foreign subnet MUST use its sends multicast packets directly on the foreign subnet MUST use its
care-of address as the IPv6 Source Address of each multicast packet. care-of address as the IPv6 Source Address of each multicast packet.
Similarly, a mobile node that tunnels a multicast packet to its home Similarly, a mobile node that tunnels a multicast packet to its home
agent MUST use its home address as the IPv6 Source Address of both agent MUST use its home address as the IPv6 Source Address of the
the (inner) multicast packet and the (outer) encapsulating packet. inner multicast packet. This second option assumes that the home
This second option assumes that the home agent is a multicast router. agent is a multicast router.
10. Constants 10. 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_ADVERT_REXMIT 3 MAX_ADVERT_REXMIT 3
11. Security Considerations 11. Security Considerations
11.1. 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
redirection", for instance as performed by the Binding Update option, redirection", for instance as performed by the Binding Update option,
is widely understood to be a security problem in the current Internet is widely understood to be a security problem in the current Internet
if not authenticated [2]. if not authenticated [2].
The Binding Acknowledgement option also requires authentication,
since, for example, an attacker could otherwise trick a mobile node
into believing a different outcome from a registration attempt with
its home agent.
No authentication is required for the Binding Request option, since
the use of this option does not modify or create any state in either
the sender or the receiver. This Option Does open some issues with
binding privacy, but those issues can be dealt with either through
existing IPsec encryption mechanisms or through use of firewalls.
The existing IPsec replay protection mechanisms allow a "replay
protection window" to support receiving packets out of order.
Although appropriate for many forms of communication, Binding Updates
MUST be applied only in the order sent. The Binding Update option
thus includes a Sequence Number field to provide this necessary
sequencing. The use of this Sequence Number together with IPsec
replay protection is similar in many ways, for example, to the the
sequence number in TCP. IPsec provides strong replay protection but
no ordering, and the sequence number provides ordering but need not
worry about replay protection such as through the sequence number
wrapping around.
11.2. Home Address Options
No special authentication of the Home Address option is required,
except that if the IPv6 header of a packet is covered by
authentication, then that authentication MUST also cover the Home
Address option. Thus, even when authentication is used 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 option. Without
authentication of the packet, then any field in the IPv6 header,
including the Source Address field, and any other parts of the
packet, including the Home Address option, can be forged or modified
in transit. In this case, the contents of the Home Address option is
no more suspect than any other part of the packet.
The use of the Home Address option allows packets sent by a
mobile node to pass normally through routers implementing ingress
filtering [6]. Since the care-of address used in Source Address
field of the packet's IPv6 header is topologically correct for the
sending location of the mobile node, ingress filtering can trace the
location of the mobile node in the same way as can be done with any
sender when ingress filtering is in use.
However, if a node receiving a packet that includes a Home Address
option implements the processing of this option by physically
copying the Home Address field from the option into the IPv6 header,
replacing the Source Address field there, then the ability to
trace the true location of the sender is removed once this step
in the processing is performed. This diminishing of the power of
ingress filtering only occurs once the packet has been received at
its ultimate destination, and does not affect the capability of
ingress filtering while the packet is in transit. Furthermore, this
diminishing can be entirely eliminated by appropriate implementation
techniques in the receiving node. For example, the original contents
of the Source Address field (the sending care-of address) could be
saved elsewhere in memory with the packet, until all processing of
the packet is completed.
11.3. General Mobile Computing Issues
The mobile computing environment is potentially very different from The mobile computing environment is potentially very different from
the ordinary computing environment. In many cases, mobile computers the ordinary computing environment. In many cases, mobile computers
will be connected to the network via wireless links. Such links will be connected to the network via wireless links. Such links
are particularly vulnerable to passive eavesdropping, active replay are particularly vulnerable to passive eavesdropping, active replay
attacks, and other active attacks. attacks, and other active attacks. Furthermore, mobile computers
are more susceptible to loss or theft than stationary computers.
Any secrets such as authentication or encryption keys stored on the
mobile computer are thus subject to compromise in ways generally not
common in the non-mobile environment.
Users who have sensitive data that they do not wish others to see Users who have sensitive data that they do not wish others to see
should use mechanisms outside the scope of this document (such as should use mechanisms outside the scope of this document (such as
encryption) to provide appropriate protection. Users concerned about encryption) to provide appropriate protection. Users concerned about
traffic analysis should consider appropriate use of link encryption. traffic analysis should consider appropriate use of link encryption.
If absolute location privacy is desired, the mobile node can create a If stronger location privacy is desired, the mobile node can create a
tunnel to its home agent. Then, packets destined for correspondent tunnel to its home agent. Then, packets destined for correspondent
nodes will appear to emanate from the home subnet, and it may be nodes will appear to emanate from the home subnet, and it may be
more difficult to pinpoint the location of the mobile node. Such more difficult to pinpoint the location of the mobile node. Such
mechanisms are all beyond the scope of this document. mechanisms are all beyond the scope of this document.
Acknowledgements Appendix A. Changes from Previous Draft
We would like to thank the members of the Mobile IP and IPng Working
Groups for their comments and suggestions on this draft. We would
particularly like to thank Thomas Narten and Erik Nordmark for
their detailed reviews of earlier versions of this draft. Their
suggestions have helped to improve both the design and presentation
of the protocol.
A. Open Issues
A.1. Session Keys with Local Routers
In the IPv4 route optimization proposal [7], a mechanism is outlined This appendix briefly lists some of the major changes in this
whereby a session key can be established between foreign agents draft relative to the previous version of this same draft,
and mobile nodes, without requiring any pre-established security draft-ietf-mobileip-ipv6-02.txt:
relationship between them. A similar mechanism could be defined for
IPv6, to avoid the need for a possibly time-consuming negotiation
between routers and mobile nodes for the purpose of obtaining the
session key, which under many circumstances would only be used once.
This mechanism, if needed, can be specified completely outside
the Mobile IPv6 protocol and would amount to a way of creating a
dynamic security association between two nodes which do not share an
existing trust relationship, but which need to agree on a key for
some particular purpose (here, allowing the future authentication of
a Binding Update). Hopefully, the work of the IP Security Working
Group will allow this function to be performed appropriately for
mobile nodes, say by a Diffie-Hellman key exchange.
A.2. Source Address Filtering by Firewalls - Added a comparison to Mobile IP for IPv4 and added this section
listing changes from the previous version of this draft.
The current specification does nothing to permit mobile nodes to - Introduced the Home Address destination option, to allow packets
send their packets through firewalls which filter out packets with sent by a mobile node while away from home to pass normally
the "wrong" source IPv6 addresses in the IPv6 packet header. The through routers implementing ingress filtering.
mobile node's home address may be unlikely to fall within the ranges
required to satisfy the firewall's criteria for further delivery.
As indicated by recent discussion, firewalls are unlikely to - Added the requirement that all IPv6 nodes MUST be able to
disappear. Any standardized solution [13] to the firewall problem correctly process a Home Address destination option in a received
based on hiding the non-local source address outside the source packet.
address field of the IP header is likely to fail. Any vendor or
facilities administrator wanting to filter based on the address in
the IPv6 source address field would also quickly begin filtering on
hidden source addresses.
Assume, for the moment, that a mobile node is able to establish a - Changed the interpretation of the Binding Update option such
secure tunnel through a firewall protecting the domain in which that the home address in the binding is the address in the Home
a correspondent node is located. The mobile node could then Address option, not the Source Address in the IPv6 header.
encapsulate its packet so that the outer IP header was addressed
to the firewall and used the mobile node's care-of address as the
source address. When the firewall decapsulates, it would be able to
authenticate the inner packet based (correctly) on the mobile node's
home address. After the authentication is performed, the firewall
could forward the packet to the correspondent node as desired. This
simple procedure has the feature that it requires the minimal amount
of encapsulation, no assistance by routers or other agents, and that
the firewall can establish a security relationship with the mobile
node based on its home (i.e., permanent) address.
A.3. Dynamic Home Agent Address Discovery - Made the Care-of Address field in the Binding Update optional,
controlled by whether or not the new Care-of Address Present (C)
bit is set in the option. With the new use of the Home Address
option, the care-of address for a binding will usually be
specified by the Source Address field in the packet's IPv6
header, but by retaining this field (and making it optional),
it is possible to send a binding update using a Source Address
different from the care-of address for the binding.
It is useful for a mobile node to be able to send a Binding Update - Changed the 32-bit Identification field in the Binding Update and
its home agent without explicitly knowing the home agent's address. Binding Acknowledgement to a 16-bit Sequence Number field, and
For example, since the mobile node was last at home, it may have clarified the use of this field. Replay protection for Binding
become necessary to replace the node serving as its home agent due Updates and Binding Acknowledgements is provided by the IPsec
to the failure of the original node or due to reconfiguration of the authentication in the packet, but this replay protection does
home subnet. It thus may not always be possible or convenient for a not provide sequencing due to the use of the replay protection
mobile node to know the exact address of its own home agent. Several window. This field satisfies that the additional sequencing
methods of allowing a mobile node to dynamically discover the address requirement.
of a router in its home subnet are currently under consideration.
A.4. Replay Protection for Binding Updates - Added a description of the dynamic home agent address discovery
procedure and the use of the new Home-Agents anycast address.
Some transforms for use in conjunction with the IP Authentication Acknowledgements
Header [1] provide support for replay protection [9, 6]. Ideally,
such transforms would directly support the needs of Mobile IPv6
for providing replay protection for Binding Updates and Binding
Acknowledgements. However, this does not currently appear to be
the case. These transforms provide optional support for accepting
packets out of order, through use of an "out of order window" in the
receiver, and it does not currently seem to be specified how the
size (or presence) of such a window can be controlled. For Binding
Updates, it is important that any packets containing a Binding
Update that arrive at the receiver do so strictly in the order sent
(although some may harmlessly be dropped, as long as a later Binding
Update does arrive). Without control of the window at the receiver,
this ordering requirement on Binding Update delivery cannot be
supported directly by these transforms, although these transforms do
use a sequence number to support their own replay protection.
The Identification field in the Binding Update (and Binding We would like to thank the members of the Mobile IP and IPng Working
Acknowledgement) is currently specified in this document for use Groups for their comments and suggestions on this work. We would
in sequencing Binding Updates at the receiver, and in matching particularly like to thank Thomas Narten and Erik Nordmark for
returned Binding Acknowledgements with outstanding Binding Updates their detailed reviews of earlier versions of this draft. Their
at the sender. The use of this field in this manner, together with suggestions have helped to improve both the design and presentation
the use of the current IP Authentication transforms that supports of the protocol.
replay protection, seems to support the necessary replay protection
requirements for Mobile IPv6, although it seems that the need for two
sequence numbers in the packet (one for IP Authentication and one for
Mobile IPv6) could be simplified.
References References
[1] Randall Atkinson. IP Authentication header. RFC 1826, August [1] Randall Atkinson. IP Authentication header. RFC 1826, August
1995. 1995.
[2] S. M. Bellovin. Security problems in the TCP/IP protocol suite. [2] S. M. Bellovin. Security problems in the TCP/IP protocol suite.
ACM Computer Communications Review, 19(2), March 1989. ACM Computer Communications Review, 19(2), March 1989.
[3] Jim Bound and Charles Perkins. Dynamic Host Configuration [3] Jim Bound and Charles Perkins. Dynamic Host Configuration
Protocol for IPv6 (DHCPv6). Internet-Draft, Protocol for IPv6 (DHCPv6). Internet-Draft,
draft-ietf-dhc-dhcpv6-07.txt, August 1996. Work in progress. draft-ietf-dhc-dhcpv6-10.txt, May 1997. Work in progress.
[4] Alex Conta and Stephen Deering. Generic packet [4] Alex Conta and Stephen Deering. Generic packet
tunneling in IPv6 specification. Internet-Draft, tunneling in IPv6 specification. Internet-Draft,
draft-ietf-ipngwg-ipv6-tunnel-02.txt, June 1996. Work draft-ietf-ipngwg-ipv6-tunnel-07.txt, December 1996.
in progress. Work in progress.
[5] Stephen E. Deering and Robert M. Hinden. Internet Protocol [5] Stephen E. Deering and Robert M. Hinden. Internet Protocol
version 6 (IPv6) specification. RFC 1883, December 1995. version 6 (IPv6) specification. RFC 1883, December 1995.
[6] Shu jen Chang and Robert Glenn. HMAC-SHA IP authentication with [6] Paul Ferguson, editor. Network ingress filtering: Defeating
replay prevention. Internet-Draft, IP source address spoofing denial of service attacks.
draft-ietf-ipsec-ah-hmac-sha-04.txt, November 1996. Work in Internet-Draft, draft-ferguson-ingress-filtering-02.txt, July
progress. 1997. Work in progress.
[7] David B. Johnson and Charles Perkins. Route optimization in [7] P. Mockapetris. Domain Names---concepts and facilities.
Mobile IP. Internet-Draft, draft-ietf-mobileip-optim-04.txt, RFC 1034, November 1987.
February 1996. Work in progress.
[8] Thomas Narten, Erik Nordmark, and William Allen Simpson. [8] P. Mockapetris. Domain Names---implementation and
specification. RFC 1035, November 1987.
[9] Thomas Narten, Erik Nordmark, and William Allen Simpson.
Neighbor Discovery for IP version 6 (IPv6). RFC 1970, August Neighbor Discovery for IP version 6 (IPv6). RFC 1970, August
1996. 1996.
[9] Michael J. Oehler and Robert Glenn. HMAC-MD5 IP [10] Charles Perkins. IP encapsulation within IP. RFC 2003, October
authentication with replay prevention. Internet-Draft, 1996.
draft-ietf-ipsec-ah-hmac-md5-04.txt, November 1996. Work in
progress.
[10] J. B. Postel. User Datagram Protocol. RFC 768, August 1980. [11] Charles Perkins, editor. IP mobility support. RFC 2002,
October 1996.
[11] J. B. Postel, editor. Transmission Control Protocol. RFC 793, [12] Charles Perkins. Minimal encapsulation within IP. RFC 2004,
October 1996.
[13] J. B. Postel. User Datagram Protocol. RFC 768, August 1980.
[14] J. B. Postel, editor. Transmission Control Protocol. RFC 793,
September 1981. September 1981.
[12] Joyce K. Reynolds and Jon Postel. Assigned numbers. RFC 1700, [15] Joyce K. Reynolds and Jon Postel. Assigned numbers. RFC 1700,
October 1994. October 1994.
[13] Fumio Teraoka. Mobility support in IPv6. Internet-Draft, [16] Susan Thomson and Thomas Narten. IPv6 stateless address
draft-teraoka-ipv6-mobility-sup-03.txt, April 1996. Work in
progress.
[14] Susan Thomson and Thomas Narten. IPv6 stateless address
autoconfiguration. RFC 1971, August 1996. autoconfiguration. RFC 1971, August 1996.
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. Motorola, Inc.
1301 E. Algonquin Rd. 1301 E. Algonquin Rd.
Schaumburg, IL 60196 Schaumburg, IL 60196
skipping to change at page 50, line 21 skipping to change at page 58, line 21
Computer Science Department Computer Science Department
5000 Forbes Avenue 5000 Forbes Avenue
Pittsburgh, PA 15213-3891 Pittsburgh, PA 15213-3891
USA USA
Phone: +1 412 268-7399 Phone: +1 412 268-7399
Fax: +1 412 268-5576 Fax: +1 412 268-5576
E-mail: dbj@cs.cmu.edu E-mail: dbj@cs.cmu.edu
Charles Perkins Charles Perkins
IBM Corporation Sun Microsystems, Inc.
T. J. Watson Research Center Technology Development Group
Room H3-D34 Mail Stop MPK15-214
30 Saw Mill River Rd. Room 2682
Hawthorne, NY 10532 901 San Antonio Road
Palo Alto, CA 94303
USA USA
Phone: +1 914 789-7350 Phone: +1 415 786-6464
Fax: +1 914 784-6205 Fax: +1 415 786-6445
E-mail: perk@watson.ibm.com E-mail: cperkins@eng.sun.com
 End of changes. 

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