draft-ietf-mobileip-ipv6-01.txt   draft-ietf-mobileip-ipv6-02.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 IBM Corporation
13 June 1996 26 November 1996
Mobility Support in IPv6 Mobility Support in IPv6
<draft-ietf-mobileip-ipv6-01.txt> <draft-ietf-mobileip-ipv6-02.txt>
Abstract Abstract
This document specifies the operation of mobile computers using IPv6. This document specifies the operation of mobile computers using IPv6.
Each mobile node is always identified by its home address, regardless Each mobile node is always identified by its home address, regardless
of its current point of attachment to the Internet. While situated of its current point of attachment to the Internet. While situated
away from its home, a mobile node is also associated with a care-of away from its home, a mobile node is also associated with a care-of
address, which provides information about the mobile node's current address, which provides information about the mobile node's current
location. IPv6 packets addressed to a mobile node's home address are location. IPv6 packets addressed to a mobile node's home address are
transparently routed to its care-of address. The protocol enables transparently routed to its care-of address. The protocol enables
skipping to change at page 1, line 55 skipping to change at page 1, line 56
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast). ftp.isi.edu (US West Coast).
Contents Contents
Abstract i Abstract i
Status of This Memo i Status of This Memo i
1. Introduction 1 1. Introduction 1
1.1. Design Requirements . . . . . . . . . . . . . . . . . . . 2
1.2. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 2
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 2
1.5. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.6. Specification Language . . . . . . . . . . . . . . . . . 5
2. Overview of Mobile IPv6 Operation 7 2. Terminology 2
2.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 2
2.2. Mobile IPv6 Terms . . . . . . . . . . . . . . . . . . . . 3
2.3. Specification Language . . . . . . . . . . . . . . . . . 4
3. Message and Option Formats 9 3. Overview of Mobile IPv6 Operation 6
3.1. Binding Update Option . . . . . . . . . . . . . . . . . . 9
3.2. ICMP Binding Acknowledgement Message . . . . . . . . . . 13
4. Requirements for IPv6 Nodes 15 4. New IPv6 Destination Options 11
4.1. Binding Update Option . . . . . . . . . . . . . . . . . . 11
4.2. Binding Acknowledgement Option . . . . . . . . . . . . . 14
4.3. Binding Request Option . . . . . . . . . . . . . . . . . 17
5. Binding Cache Management 17 5. Requirements for IPv6 Nodes 18
5.1. Receiving Binding Updates . . . . . . . . . . . . . . . . 17
5.2. Requests to Cache a Binding . . . . . . . . . . . . . . . 17
5.3. Requests to Delete a Binding . . . . . . . . . . . . . . 18
5.4. Sending Binding Acknowledgements . . . . . . . . . . . . 18
5.5. Cache Replacement Policy . . . . . . . . . . . . . . . . 19
5.6. Receiving ICMP Error Messages . . . . . . . . . . . . . . 19
6. Mobile Node Considerations 21 6. Correspondent Node Operation 20
6.1. Movement Detection . . . . . . . . . . . . . . . . . . . 21 6.1. Receiving Binding Updates . . . . . . . . . . . . . . . . 20
6.2. Forming New Care-of Addresses . . . . . . . . . . . . . . 23 6.2. Requests to Cache a Binding . . . . . . . . . . . . . . . 21
6.3. Sending Binding Updates to the Home Agent . . . . . . . . 24 6.3. Requests to Delete a Binding . . . . . . . . . . . . . . 21
6.4. Sending Binding Updates to Correspondent Nodes . . . . . 25 6.4. Sending Binding Acknowledgements . . . . . . . . . . . . 21
6.5. Sending Binding Updates to the Previous Default Router . 25 6.5. Cache Replacement Policy . . . . . . . . . . . . . . . . 22
6.6. Rate Limiting for Sending Binding Updates . . . . . . . . 26 6.6. Receiving ICMP Error Messages . . . . . . . . . . . . . . 23
6.7. Receiving Binding Acknowledgements . . . . . . . . . . . 26 6.7. Sending Packets to a Mobile Node . . . . . . . . . . . . 24
6.8. Using Multiple Care-of Addresses . . . . . . . . . . . . 27
6.9. Returning Home . . . . . . . . . . . . . . . . . . . . . 28
7. Home Agent Considerations 29 7. Home Agent Operation 26
7.1. Home Agent Care-of Address Registration . . . . . . . . . 29 7.1. Primary Care-of Address Registration . . . . . . . . . . 26
7.2. Home Agent Care-of Address De-registration . . . . . . . 31 7.2. Primary Care-of Address De-registration . . . . . . . . . 28
7.3. Delivering Packets to a Mobile Node . . . . . . . . . . . 32 7.3. Tunneling Intercepted Packets to a Mobile Node . . . . . 28
7.4. Renumbering the Home Network . . . . . . . . . . . . . . 32 7.4. Renumbering the Home Subnet . . . . . . . . . . . . . . . 29
8. Correspondent Node Considerations 34 8. Mobile Node Operation 31
8.1. Delivering Packets to a Mobile Node . . . . . . . . . . . 34 8.1. Movement Detection . . . . . . . . . . . . . . . . . . . 31
8.2. Forming New Care-of Addresses . . . . . . . . . . . . . . 33
8.3. Sending Binding Updates to the Home Agent . . . . . . . . 34
8.4. Sending Binding Updates to Correspondent Nodes . . . . . 35
8.5. Sending Binding Updates to the Previous Default Router . 37
8.6. Retransmitting Binding Updates . . . . . . . . . . . . . 37
8.7. Rate Limiting for Sending Binding Updates . . . . . . . . 38
8.8. Receiving Binding Acknowledgements . . . . . . . . . . . 38
8.9. Using Multiple Care-of Addresses . . . . . . . . . . . . 39
8.10. Returning Home . . . . . . . . . . . . . . . . . . . . . 39
9. Authentication and Replay Protection 36 9. Routing Multicast Packets 41
10. Routing Multicast Packets 37 10. Constants 42
11. Constants 38 11. Security Considerations 43
Acknowledgements 38 Acknowledgements 44
References 39 A. Open Issues 45
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
A. Open Issues 40 References 47
A.1. Session Keys with Local Routers . . . . . . . . . . . . . 40
A.2. Source Address Filtering by Firewalls . . . . . . . . . . 40
Chair's Address 42 Chair's Address 49
Authors' Addresses 42 Authors' Addresses 50
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) [6]. Mobile computers are likely Internet Protocol Version 6 (IPv6) [5]. Without specific support for
to account for a majority or at least a substantial fraction of mobility in IPv6, packets destined to a mobile node (host or router)
the population of the Internet during the lifetime of IPv6. The would not be able to reach it while the mobile node is away from its
protocol, known as Mobile IPv6, allows transparent routing of IPv6 home IPv6 subnet, since routing is based on the network prefix in a
packets to mobile nodes using the mobile node's home IPv6 address, packet's destination IP address. In order continue communication
regardless of the mobile node's current point of attachment to the in spite of its movement, a mobile node could change its IP address
Internet. each time it moves to a new IPv6 subnet, but the mobile node would
then not be able to maintain transport and higher-layer connections
The most important function needed to support such routing to mobile when it changes location. Mobility support in IPv6 is particularly
nodes is the reliable and timely notification of a mobile node's important, as mobile computers are likely to account for a majority
current location to those other nodes that need it. Correspondent or at least a substantial fraction of the population of the Internet
nodes communicating with a mobile node need this location information during the lifetime of IPv6.
in order to correctly deliver their own packets to a mobile node;
Mobile IPv6 allows correspondent nodes to learn and cache a mobile
node's location, and to use this cached information to route their
own packets directly to a mobile node at its current location. The
mobile node's "home agent", a router on the mobile node's home
network, also needs this location information in order to forward
intercepted packets from the home network to the mobile node, for
correspondent nodes that have not yet learned the mobile node's
location, and indeed, for correspondent nodes that do not even yet
know that the mobile node is currently away from home.
A mobile node's current location is represented as a "care-of
address", an IPv6 address assigned to the mobile node (in addition
to its home IPv6 address) within the foreign network currently being
visited by the mobile node. The association between a mobile node's
home address and its care-of address, along with the remaining
lifetime of that association, is known as a "binding", and the mobile
node notifies other nodes about its current binding using a new
destination option called a Binding Update. IPv6 correspondent nodes
then use a Routing header to deliver subsequent packets to the mobile
node's care-of address. All IPv6 nodes and routers MUST be able to
cache mobile node bindings received in Binding Updates; this leads to
dramatic simplifications in the required protocols, compared to the
methods required for IPv4.
In this document, "movement" is considered to be 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 IPv6 subnet (network prefix) as
it was previously. If a mobile node is not currently link-level
connected to its home IPv6 network, the mobile node is said to be
"away from home".
1.1. Design Requirements The protocol operation defined here, known as Mobile IPv6, allows a
mobile node to move from one IPv6 subnet to another without changing
the mobile node's IP address. A mobile node is always addressable
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
address regardless of the mobile node's current point of attachment
to the Internet, and the mobile node may continue to communicate with
other nodes (stationary or mobile) after moving to a new subnet.
The movement of a mobile node away from its home subnet is thus
transparent to transport and higher-layer protocols and applications.
A mobile node must continue to be able to be addressed by its home The Mobile IPv6 protocol is just as suitable for mobility across
IPv6 address, and to be able to communicate with other IPv6 nodes homogeneous media as for mobility across heterogeneous media. For
using its home address, after changing its link-level point of example, Mobile IPv6 facilitates node movement from one Ethernet
attachment from one IPv6 subnet to another. segment to another as well as it accommodates node movement from an
Ethernet segment to a wireless LAN cell, as long as the mobile node's
IP address remains unchanged after such a movement.
All messages used to update another node as to the location of a One can think of the Mobile IPv6 protocol as solving the "macro"
mobile node must be authenticated in order to protect against remote mobility management problem. More "micro" mobility management
redirection attacks. applications -- for example, handoff amongst wireless transceivers,
each of which covers only a very small geographic area, are possibly
more suited to other solutions. For example, as long as node
movement does not occur between link-level points of attachment on
different IPv6 subnets, link-layer mobility support offered by a
number of current wireless LAN products is likely to offer faster
convergence and lower overhead than Mobile IPv6. Extensions to the
Mobile IPv6 protocol are also possible to support a more local,
hierarchical form of handoff, but such extensions are beyond the sope
of this document.
1.2. Goals 2. Terminology
The number of administrative messages sent over the link by which 2.1. General Terms
a mobile node is directly attached to the Internet should be
minimized, and the size of these messages should be kept as small
as is reasonably possible. This link may often be a wireless link,
having a substantially lower bandwidth and higher error rate than
traditional wired networks, and many mobile nodes are likely to
operate on limited battery power. By reducing the number and size
of administrative messages required for mobility support, network
resources and mobile node battery resources are conserved.
1.3. Assumptions IP
This protocol places no additional constraints on the assignment of Internet Protocol Version 6 (IPv6).
IPv6 addresses. That is, a mobile node may acquire its addresses
using stateless address autoconfiguration [12], or alternatively
using a stateful address configuration protocol such as DHCPv6 [3] or
PPPv6 [7].
This protocol assumes that any mobile node will generally not change node
its link-level point of attachment from one IPv6 subnet to another
more frequently than once per second.
This protocol assumes that IPv6 unicast packets are routed based on A device that implements IP.
the Destination Address in the packet's IPv6 header (and not, for
example, by source address).
1.4. Applicability router
Mobile IPv6 is intended to enable nodes to move from one IPv6 subnet A node that forwards IP packets not explicitly addressed to
to another. It is just as suitable for mobility across homogeneous itself.
media as it is for mobility across heterogeneous media. That is,
Mobile IPv6 facilitates node movement from one Ethernet segment to
another as well as it accommodates node movement from an Ethernet
segment to a wireless LAN, as long as the mobile node's IPv6 address
remains the same after such a movement.
One can think of Mobile IPv6 as solving the "macro" mobility host
management problem. It is less well suited for more "micro" mobility
management applications -- for example, handoff amongst wireless
transceivers, each of which covers only a very small geographic
area. As long as node movement does not occur between link-level
points of attachment on different IPv6 subnets, link-layer mechanisms
for mobility management (i.e., link-layer handoff) may offer faster
convergence and far less overhead than Mobile IPv6.
1.5. Terminology Any node that is not a router.
This document uses the following special terms: link
Binding A communication facility or medium over which nodes can
communicate at the link layer, such as an Ethernet (simple or
bridged). A link is the layer immediately below IP.
The association of the home address of a mobile node with a interface
care-of address for that mobile node, along with the remaining
lifetime of that association.
Binding Cache A node's attachment to a link.
A cache, maintained by each IPv6 node, of bindings for other network prefix
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"
entry and SHOULD NOT be deleted by the node until the
expiration of its binding lifetime, whereas other Binding Cache
entries MAY be replaced at any time by any reasonable local
cache replacement policy. The Binding Cache is a conceptual
data structure used in this document, which may be implemented
in any manner consistent with the external behavior described
here, for example by being combined with the node's Destination
Cache as maintained through Neighbor Discovery [9].
Binding Update List A bit string that consists of some number of initial bits of an
IP address.
A list, maintained by each IPv6 mobile node, of the IPv6 link-layer address
address of each other node to which this node has sent a
Binding Update giving its binding, such that the lifetime of
the binding sent to that node has not yet expired. This is a
conceptual data structure used in this document, which may be
implemented in any manner consistent with the external behavior
described here.
Care-of Address A link-layer identifier for an interface, such as IEEE 802
addresses on Ethernet links.
An IPv6 address associated with a mobile node while visiting a packet
foreign network, which uses the network prefix of that foreign
network. Among the multiple care-of addresses that a mobile
node may have at a time (with different network prefixes), the
one registered with its home agent is called its "primary"
care-of address.
Correspondent Node An IP header plus payload.
A peer with which a mobile node is communicating. The 2.2. Mobile IPv6 Terms
correspondent node may be either mobile or stationary.
Foreign Network home address
Any network other than the mobile node's home network. An IP address assigned to a mobile node within its home subnet.
The network prefix in a mobile node's home address is equal to
the network prefix of the home subnet.
Home Address home subnet
An IPv6 address that is assigned for an extended period of The IP subnet indicated by a mobile node's home address.
time to a mobile node. It remains unchanged regardless of the Standard IP routing mechanisms will deliver packets destined
node's current link-level point of attachment to the Internet. for a mobile node's home address to its home subnet.
Home Agent mobile node
A router on a mobile node's home network that, while the mobile A node that can change its link-level point of attachment from
node is away from home, intercepts packets on the home network one IP subnet to another, while still being addressable via its
destined to the mobile node's home address, encapsulates them, home address.
and tunnels them to the mobile node's current care-of address.
The home agent maintains a registry of the current binding for
mobile nodes whose home address is on the home network routed
by the home agent.
Home Network movement
A network, which may possibly be a virtual network, having a A change in a mobile node's point of attachment to the Internet
network prefix matching that of a mobile node's home address. such that it is no longer link-level connected to the same IP
Standard IPv6 routing mechanisms will deliver packets destined subnet as it was previously. If a mobile node is not currently
for a mobile node's home address to the mobile node's home link-level connected to its home subnet, the mobile node is
network. said to be "away from home".
Link correspondent node
A facility or medium over which nodes can communicate at the A peer with which a mobile node is communicating. The
link layer. A link underlies the network layer. correspondent node may be either mobile or stationary.
Mobile Node foreign subnet
A node that can change its link-level point of attachment from Any IP subnet other than the mobile node's home subnet.
one IPv6 subnet to another, while still being addressable via
its IPv6 home address.
Node home agent
A host or a router. A router on a mobile node's home subnet with which the mobile
node has registered its current care-of address. While the
mobile node is away from home, the home agent intercepts
packets on the home subnet destined to the mobile node's home
address, encapsulates them, and tunnels them to the mobile
node's registered care-of address.
Tunnel care-of address
The path followed by a packet while it is encapsulated. The An IP address associated with a mobile node while visiting
model is that, while it is encapsulated, a packet is routed a foreign subnet, which uses the network prefix of that
to a knowledgeable decapsulating agent, which decapsulates foreign subnet. Among the multiple care-of addresses that a
the packet and then correctly delivers it to its ultimate mobile node may have at a time (e.g., with different network
destination. prefixes), the one registered with its home agent is called its
"primary" care-of address.
Virtual Network binding
A network with no physical instantiation beyond a home agent The association of the home address of a mobile node with a
(with a physical network interface on another network). The care-of address for that mobile node, along with the remaining
home agent generally advertises reachability to the network lifetime of that association.
prefix of the virtual network using conventional routing
protocols.
1.6. 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
of the specification. These words are often capitalized. of the specification. These words are often capitalized.
MUST MUST
This word, or the adjective "required", means that the This word, or the adjective "REQUIRED", means that the
definition is an absolute requirement of the specification. definition is an absolute requirement of the specification.
MUST NOT MUST NOT
This phrase means that the definition is an absolute This phrase means that the definition is an absolute
prohibition of the specification. prohibition of the specification.
SHOULD SHOULD
This word, or the adjective "recommended", means that, in some This word, or the adjective "RECOMMENDED", means that there may
circumstances, valid reasons may exist to ignore this item, but exist valid reasons in particular circumstances to ignore a
the full implications must be understood and carefully weighed particular item, but the full implications must be understood
before choosing a different course. Unexpected results may and carefully weighed before choosing a different course.
result otherwise.
SHOULD NOT
This phrase means that there may exist valid reasons in
particular circumstances when the particular behavior is
acceptable or even useful, but the full implications should be
understood and the case carefully weighed before implementing
any behavior described with this label.
MAY MAY
This word, or the adjective "optional", means that this item is This word, or the adjective "OPTIONAL", means that an item
one of an allowed set of alternatives. An implementation which is truly optional. For example, one vendor may choose to
does not include this option MUST be prepared to interoperate include the item because a particular marketplace requires
with another implementation which does include the option. it or because the vendor feels that it enhances the product,
while another vendor may omit the same item. An implementation
which does not include a particular option MUST be prepared to
interoperate with another implementation which does include the
option.
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.
2. Overview of Mobile IPv6 Operation 3. Overview of Mobile IPv6 Operation
In addition to its (permanent) IPv6 home address, a mobile node A mobile node is always addressable by its home address, whether it
while away from home will have assigned to its network interface(s) is currently attached to its home subnet or is away from home. While
a "primary care-of address" and possibly other "care-of addresses". a mobile node is at home, packets addressed to the mobile node's
A care-of address is an IPv6 address assigned to a mobile node only home address are routed to it using conventional Internet routing
while visiting a particular foreign network, typically acquired mechanisms in the same way as if the node were never mobile. Since
through stateless [12] or stateful (e.g., DHCPv6 [3]) address the network prefix of a mobile node's home address is equal to the
autoconfiguration. The decision about which manner of address network prefix of its home subnet, packets addressed to it will be
autoconfiguration to use is made according to the methods of IPv6 routed to its home subnet.
Neighbor Discovery [9].
Each time a mobile node moves its link-level point of attachment from While a mobile node is attached to some foreign subnet away from
one IPv6 subnet to another, it will configure its primary care-of home, it is also addressable by one or more care-of addresses, in
address at its new point of attachment, and will send a Binding addition to its home address. A care-of address is an IP address
Update containing that care-of address to its home agent. The associated with a mobile node only while visiting a particular
care-of address for a mobile node registered with its home agent is foreign subnet. The network prefix of a care-of address being used
known as the mobile node's "primary" care-of address, and the mobile by a mobile node is equal to the network prefix of the foreign
node may also have additional care-of addresses, one for each of the subnet to which the mobile node is link-level connected, and thus
network prefixes that it currently considers to be on-link. Each packets addressed to this care-of address will be routed to the
time it changes its primary care-of address, a mobile node also sends mobile node's location away from home. The association between
a Binding Update to each other (correspondent) node that may have an a mobile node's home address and care-of address is known as a
out-of-date care-of address for the mobile node in its Binding Cache. "binding" for the mobile node. A mobile node typically acquires its
care-of address through stateless [14] or stateful (e.g., DHCPv6 [3])
address autoconfiguration, according to the methods of IPv6 Neighbor
Discovery [8], although other methods of acquiring a care-of address
are also possible.
A mobile node attached to the Internet can always be reached by While away from home, the mobile node registers one of its binding
sending packets to its home IPv6 address. If the mobile node is not with a router in its home subnet, requesting this router to function
present on its home network, any packet arriving there for it will be as the "home agent" for the mobile node. The care-of address in this
intercepted there by its home agent, which will tunnel the packet to binding registered with its home agent is known as the mobile node's
the mobile node's current primary care-of address. The home agent "primary care-of address". The mobile node's home agent thereafter
uses IPv6 encapsulation [5] to tunnel the packet. 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
packet using IPv6 encapsulation [4], addressed to the mobile node's
primary care-of address.
A correspondent node sending a packet checks its Binding Cache for Mobile IPv6 provides a mechanism for IPv6 nodes communicating with
an entry for the Destination Address of the packet, and uses a a mobile node, to dynamically learn and cache the mobile node's
Routing header (instead of encapsulation) to route the packet to the binding. When sending a packet to any IPv6 destination, a node
destination mobile node's care-of address if a cached binding is checks its cached bindings for an entry for the packet's destination
found. Otherwise, the correspondent node sends the packet normally address. If a cached binding for this destination address is
(with no Routing header), and the packet is then intercepted and found, the node uses an IPv6 Routing header [5] (instead of IPv6
tunneled by the mobile node's home agent as described above. When encapsulation) to route the packet to the mobile node through the
the tunneled packet reaches the mobile node, the mobile node returns care-of address indicated in this binding. If, instead, the sending
a Binding Update to the correspondent node, allowing it to cache the node has no cached binding for this destination address, the node
mobile node's binding for future packets. sends the packet normally (with no Routing header), and the packet
is subsequently intercepted and tunneled by the mobile node's home
agent as described above. A 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
cache the mobile node's binding through use of a set of new IPv6
destination options [5] defined for Mobile IPv6. Since an IPv6
Destination Options header containing one or more destination options
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
carrying any payload such as TCP [11] or UDP [10].
- A Mobile IPv6 option can be sent as a separate IPv6 packet
containing no payload. In this case, the Next Header field
in the Destination Options header is set to the value 59, to
indicate "No Next Header" [5].
The following three new IPv6 destination options are defined for
Mobile IPv6:
Binding Update
A Binding Update is used by a mobile node to notify a
correspondent node or its home agent of its current binding.
The Binding Update sent to the mobile node's home agent is
marked as a "home registration". Any packet that includes a
Binding Update option MUST also include an IPv6 Authentication
header [1]. The Binding Update option is described in detail
in Section 4.1.
Binding Acknowledgement
A Binding Acknowledgement is used to acknowledge receipt of
a Binding Update, if an acknowledgement was requested in the
Binding Update. Other Binding Updates MAY be acknowledged
but need not be. Any packet that includes a Binding
Acknowledgement option MUST also include an IPv6 Authentication
header [1]. The Binding Acknowledgement option is described in
detail in Section 4.2.
Binding Request
A Binding Request is used to request a mobile node to send a
Binding Update to this node, containing its current binding.
This option is typically used by a correspondent node to
refresh a cached binding for a mobile node, when the lifetime
on this cached binding is close to expiration. The Binding
Request option is described in detail in Section 4.3.
Extensions to the format of these options may be included after the
fixed portion of the option data specified in this document. The
presence of such extensions will be indicated by the Option Length
field within the option. When the Option Length is greater than the
length required for the option specified here, the remaining octets
are interpreted as extensions. Currently, no extensions have been
defined.
This document describes the Mobile IPv6 protocol in terms of the
following two conceptual data structures used in the maintenance of
cached bindings:
Binding Cache
A cache, maintained by each IPv6 node, of bindings for other
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"
entry and SHOULD NOT be deleted by the home agent until the
expiration of its binding lifetime, whereas other Binding Cache
entries MAY be replaced at any time by any reasonable local
cache replacement policy. 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 [8].
Binding Update List
A list, maintained by each mobile node, recording information
for each Binding Update sent by this mobile node, for which
the Lifetime of the binding sent in that Update has not yet
expired. For each such Binding Update, the Binding Update List
records the IP address of the node to which the Update was
sent, the home address for which the Update was sent, and the
remaining lifetime of the binding. The Binding Update List
MAY be implemented in any manner consistent with the external
behavior described in this document.
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
node registers this new binding with its home agent by sending
the home agent a Binding Update. The mobile node indicates
that an acknowledgement is needed for this Binding Update and
continues to periodically retransmit it until acknowledged. The
home agent acknowledges the Binding Update by returning a Binding
Acknowledgement to the mobile node.
When a mobile node receives a packet tunneled to it from its
home agent, the mobile node assumes that the original sending
correspondent node has no binding cache entry for the mobile node,
since the correspondent node would otherwise have sent the packet
directly to the mobile node using a Routing header. The mobile node
thus returns a Binding Update to the correspondent node, allowing
it to cache the mobile node's binding for routing future packets.
Although the mobile node may request an acknowledgement for this
Binding Update, it need not, since subsequent packets from the
correspondent node will continue to be intercepted and tunneled by
the mobile node's home agent, effectively causing any needed Binding
Update retransmission.
A correspondent node with a binding cache entry for a mobile node
may refresh this binding, for example if the binding's lifetime
is near expiration, by sending a Binding Request to the mobile
node. Normally, a correspondent node will only refresh a binding
cache entry in this way if it is actively communicating with the
mobile node and has indications, such as an open TCP connection to
the mobile node, that it will continue this communication in the
future. When a mobile node receives a Binding Request, it replies by
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,
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
agent will tunnel all intercepted packets for the mobile node to its
registered primary care-of address, but the mobile node will accept
packets that it receives at any of its current care-of addresses.
Use of more than one care-of address by a mobile node may be useful,
for example, to improve smooth handoff when the mobile node moves
from one wireless IP subnet to another. If each wireless subnet is
connected to the Internet through a separate base station, such that
the wireless transmission range from the two base stations overlap,
the mobile node may be able to remain link-level connected within
both subnets while in the area of overlap. In this case, the mobile
node could acquire a new care-of address in the new subnet before
moving out of transmission range and link-level disconnecting from
the old subnet. The mobile node may thus still accept packets at
its old care-of address while it works to update its home agent and
correspondent nodes, notifying them of its new care-of address.
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 between the correspondent node and 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
network. 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 network, or intervening networks leading to the home agent, the home subnet, or intervening networks leading to the
home network is drastically reduced, since these components are not home subnet is reduced, since these nodes and links are not involved
involved in the delivery of most packets to the mobile node. in the delivery of most packets to the mobile node.
3. Message and Option Formats
3.1. Binding Update Option 4. New IPv6 Destination Options
A Binding Update is a new IPv6 destination option, used by a mobile 4.1. Binding Update Option
node to notify a correspondent node or its home agent of its current
care-of address. As a destination option, it can appear in a
Destination Options header in any IPv6 packet [6], and thus can be
included in any normal data packet or can be sent in a separate
packet containing no data. The Binding Update contains the mobile
node's care-of address, an identification for the Update (to sequence
Updates and to protect against attempts to replay it), and a lifetime
for the binding. The mobile node's IPv6 home address MUST be the
source address of the packet containing the Binding Update, since
the option does not contain space to separately represent the mobile
node's home address.
Binding Updates should be considered a form of routing updates; The Binding Update destination option is used by a mobile node to
handled incorrectly, they could be a source of security problems and notify a correspondent node or its home agent of a new care-of
routing loops. Therefore, packets which include Binding Updates MUST address.
also include an IPv6 Authentication header [1]; sequencing and replay
protection is then achieved by use of the Identification field in the
Binding Update.
The Binding Update option is encoded in type-length-value (TLV) The Binding Update option is encoded in type-length-value (TLV)
format as follows: format as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | | Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L| Reserved | Lifetime | |A|H|L| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | Identification |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ Care-of Address + + Care-of Address +
| | | |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ + + +
| | | |
+ Home Link-Local Address + + Home Link-Local Address +
| (only present if L bit set) | | (only present if L bit set) |
+ + + +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type Option Type
16 192 ???
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, this field
must be set to 28. MUST be set to 24 if the Home Link-Local Address Present (L)
bit is not set, and MUST otherwise be set to 40.
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 message be returned upon receipt of the Binding Acknowledgement (Section 4.2) be returned upon receipt
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 IPv6 header of the packet The Destination Address in the IP header of the packet carrying
carrying this option MUST be that of a router sharing the same this option MUST be that of a router sharing the same network
network prefix as the mobile node's home IPv6 address. prefix as the home address of the mobile node in the binding.
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 mobile 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.
Reserved Reserved
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 Identification
a 64-bit number used to sequence Binding Updates and to match a 32-bit number used by the receiving node to sequence Binding
a returned Binding Acknowledgement message with this Binding Updates, and by the sending node to match a returned Binding
Update. The Identification field also serves to protect Acknowledgement message with this Binding Update.
against replay attacks for Binding Updates.
Care-of Address Care-of Address
The current care-of address of the mobile node. When set equal The care-of address of the mobile node for this binding. When
to the home address of the mobile node, the Binding Update set equal to the home address of the mobile node, the Binding
option instead indicates that any existing binding for the Update option instead indicates that any existing binding for
mobile node should be deleted; no binding for the mobile node the mobile node should be deleted; no binding for the mobile
should be created. node should be created in this case.
Home Link-Local Address Home Link-Local Address
The link-local address of the mobile node used by the mobile The link-local address of the mobile node used by the mobile
node when it was last attached to its home network. This field node when it was last attached to its home subnet. This field
in the Binding Update is optional and is only present when the in the Binding Update is optional and is only present when the
Home Link-Local Address (L) bit is set. Home Link-Local Address (L) bit is set.
As with all IPv6 options, the highest-order three bits of the Option The home address of the mobile node in the binding is indicated by
Type Field (16) of the Binding Update option specify the following the Source Address field in the IP header of the packet containing
properties of the option: the Binding Update option.
- The highest-order two bits are 00: Any node receiving this Any packet that includes a Binding Update option MUST include an IPv6
option that does not recognize the Option Type MUST skip over Authentication header [1] in order to protect against forged Binding
this option and continue processing the header. Updates.
- The third-highest-order bit is 0: The Option Data does not The three highest-order bits of the Option Type are encoded to
change en-route, and thus, when an Authentication header is indicate specific processing of the option [5]. For the Binding
present in the packet, the entire Binding Update option MUST be Update option, these three bits are set to 110, indicating that the
included when computing or verifying the packet's authenticating data within the option cannot change en-route to the packet's final
value. 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 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 fixed portion of the Binding Update option specified above. The
The presence of such extensions will be indicated by the Option presence of such extensions will be indicated by the Option Length
Length field. When the Option Length is greater than 28 octets, field. When the Option Length is greater than 24 octets if the Home
the remaining octets are interpreted as extensions. Currently no Link-Local Address (L) bit is not set, or greater than 40 octets if
extensions have been defined. the Home Link-Local Address (L) bit is set, the remaining octets
are interpreted as extensions. Currently, no extensions have been
3.2. ICMP Binding Acknowledgement Message defined.
A Binding Acknowledgement message is an informational ICMP message
used to acknowledge acceptance of a Binding Update (Section 3.1)
option, if that Binding Update has the Acknowledge (A) bit set.
Upon receipt of a Binding Update requesting an acknowledgement, the 4.2. Binding Acknowledgement Option
receiving node returns a Binding Acknowledgement message addressed to
the care-of address in the Binding Update.
If a mobile node fails to receive an acceptable Binding The Binding Acknowledgement destination option is used to acknowledge
Acknowledgement message within INITIAL_BINDACK_TIMEOUT seconds receipt of a Binding Update option (Section 4.1). When a node
after transmitting the Binding Update, it SHOULD retransmit the receives a Binding Update addressed to itself, in which the
Binding Update until a Binding Acknowledgement is received. Such a Acknowledge (A) bit set, it MUST return a Binding Acknowledgement.
retransmitted Binding Update MUST use he same Identification value as
the original transmission. The retransmissions by the mobile node
MUST use an exponential back-off process, in which timeout period
is doubled upon each retransmission until either the node receives
a Binding Acknowledgement message or the timeout period reaches the
value MAX_BINDACK_TIMEOUT.
The ICMP Binding Acknowledgement message has the following format: The Binding Acknowledgement option is encoded in type-length-value
(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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum | | Refresh | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | Identification |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type Option Type
133 193 ???
Code 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 Binding Acknowledgement option, this
field MUST be set to 8.
Status
8-bit unsigned integer indicating the disposition of the 8-bit unsigned integer indicating the disposition of the
Binding Update. Values of the Code 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 values are currently defined: node. The following such Status values are currently defined:
0 Binding Update accepted 0 Binding Update accepted
Values of the Code field greater than or equal to 128 indicate
that the Binding Update was rejected by the receiving node. Values of the Status field greater than or equal to 128
The following such values are currently defined: indicate that the Binding Update was rejected by the receiving
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 network 133 Not home subnet
134 Identification field mismatch 134 Identification field mismatch
135 Unknown home agent address 135 Unknown home agent address
Checksum Up-to-date values of the Status field are to be specified in
the most recent "Assigned Numbers" [12].
The checksum of the message calculated as specified for ICMP Refresh
for IPv6 [4].
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
The granted lifetime for which this node will attempt to retain
the entry for this mobile node in its binding cache. If the
node sending the Binding Acknowledgement is serving as the
mobile node's home agent, the Lifetime period also indicates
the period for which this node will continue this service; if
the mobile node requires home agent service from this node
beyond this period, the mobile node MUST send a new Binding
Update to it before the expiration of this period to extend the
lifetime.
Identification Identification
The acknowledgement Identification is derived from the Binding The acknowledgement Identification is copied from the Binding
Update option, for use by the mobile node in matching the Update option, for use by the mobile node in matching the
acknowledgement with an outstanding Binding Update. acknowledgement with an outstanding Binding Update.
Up-to-date values of the Code field are to be specified in the most Any packet that includes a Binding Acknowledgement option MUST
recent "Assigned Numbers" [10]. include an IPv6 Authentication header [1] in order to protect against
forged Binding Acknowledgements.
Extensions to the Binding Acknowledgement message format may be If the node returning the Binding Acknowledgement accepted the
Binding Update for which the Acknowledgement is being returned (the
value of the Status field in the Acknowledgement is less than 128),
this node will have an entry for the mobile node in its Binding
Cache, and MUST use this entry (which includes the care-of address
received in the Binding Update) in sending the packet containing the
Binding Acknowledgement to the mobile node. The details of sending
this packet to the mobile node are the same as for sending any packet
to a mobile node using a Binding Cache entry, and are described in
Section 6.7. The packet is sent using a Routing header, routing the
packet to the mobile node through its care-of address recorded in the
Binding Cache entry.
If the node returning the Binding Acknowledgement instead
rejected the Binding Update (the value of the Status field in the
Acknowledgement is greater than or equal to 128), this node MUST
similarly use a Routing header in sending the packet containing the
Binding Acknowledgement, as described in Section 6.7, but MUST NOT
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
sending the packet containing the Binding Acknowledgement MUST be
copied from the care-of address received in the rejected Binding
Update; this node MUST NOT modify its Binding Cache in response
to receiving this rejected Binding Update and MUST ignore its
Binding Cache in sending the packet in which it returns this Binding
Acknowledgement. The packet is sent using a Routing header, routing
the packet to the Source Address of the rejected Binding Update
through the care-of address indicated in the Binding Update.
The three highest-order bits of the Option Type are encoded to
indicate specific processing of the option [5]. For the Binding
Acknowledgement 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 Binding Acknowledgement option format may be
included after the fixed portion of the Binding Acknowledgement included after the fixed portion of the Binding Acknowledgement
message specified above. The presence of such extensions will be option specified above. The presence of such extensions will be
indicated by the ICMP message length, derived from the IPv6 Payload indicated by the Option Length field. When the Option Length is
Length field. When the Option Length is greater than 16 octets, greater than 8 octets, the remaining octets are interpreted as
the remaining octets are interpreted as extensions. Currently no extensions. Currently, no extensions have been defined.
4.3. Binding Request Option
The Binding Request destination option is used to request a mobile
node's binding from the mobile node. When a mobile node receives
a packet containing a Binding Request option, it SHOULD return a
Binding Update (Section 4.1) to that node.
The Binding Request option is encoded in type-length-value (TLV)
format as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
194 ???
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 Binding Acknowledgement option, this
field MUST be set to 0.
The three highest-order bits of the Option Type are encoded to
indicate specific processing of the option [5]. For the Binding
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
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 Binding Request option format may be included after
the fixed portion of the Binding Request option specified above.
The presence of such extensions will be indicated by the Option
Length field. When the Option Length is greater than 0 octets,
the remaining octets are interpreted as extensions. Currently, no
extensions have been defined. extensions have been defined.
4. 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 itemizes 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 of a mobile Since any IPv6 node may at any time be a correspondent node of a
node, all IPv6 nodes MUST support the following requirements: mobile node, the following requirements pertain to all IPv6 nodes:
- Every IPv6 node MUST be able to process a received Binding Update - Every IPv6 node SHOULD be able to process a received Binding
option, and to return a Binding Acknowledgement message if Update option, and to return a Binding Acknowledgement message if
requested. requested.
- Every IPv6 node MUST 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.
- Every IPv6 node MUST be able to maintain Security Associations In order for a mobile node to operate correctly while away from
for use in IPv6 Authentication Headers [2, 1, 6]. An IPv6 home, at least one IPv6 router in the mobile node's home subnet must
node receiving a packet containing a Binding Update option function as a home agent for the mobile node. The following special
MUST verify, using the Authentication Header in the packet, requirements pertain to all IPv6 routers capable of serving as a home
the authenticity of the sender (the mobile node for which this agent:
binding applies) before modifying its Binding Cache in response
to that Binding Update option.
Since any IPv6 router may at any time have a Binding Cache entry
for a mobile node, all IPv6 router MUST support the following
requirement:
- Every IPv6 router MUST be able to use its Binding Cache in
forwarding packets; if the router has a Binding Cache entry for
the Destination Address of a packet it is forwarding, then the
router SHOULD encapsulate the packet and tunnel it to the care-of
address in the Binding Cache entry.
In order for a mobile node to correctly operate while away from
home, at least one IPv6 router in its home network must support
functioning as a home agent for the mobile node. All IPv6 routers
capable of serving as a home agent MUST support the following special
requirements:
- Every home agent MUST be able to maintain a registry of mobile - Every home agent MUST be able to maintain a registry of mobile
node bindings for those mobile nodes for which it is serving as node bindings, recording each mobile node's primary care-of
the home agent. address, for those mobile nodes for which it is serving as the
home agent.
- Every home agent MUST be able to intercept packets (e.g., using - Every home agent MUST be able to intercept packets (using proxy
Neighbor Advertisements) on the local network addressed to Neighbor Discovery) on the local subnet addressed to a mobile
a mobile node for which it holds a binding in its registry node for which it is currently serving as the home agent while
indicating that the mobile node is currently 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 care-of address for the packets in order to tunnel them to the primary care-of address
mobile node indicated in its binding. for the mobile node indicated in its binding.
- Every home agent MUST be able to issue Binding Acknowledgement
messages in response to Binding Updates received from a mobile
node.
- Every home agent MUST be able to maintain Security Associations - Every home agent MUST be able to return Binding Acknowledgements
for the mobile nodes from which it will accept Binding Updates. in response to Binding Updates received from a mobile node.
Finally, all IPv6 nodes capable of functioning as mobile nodes MUST Finally, the following requirements pertain all IPv6 nodes capable of
support the following requirements: 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 [5]. decapsulation [4].
- Every IPv6 mobile node MUST support sending Binding Updates, - Every IPv6 mobile node MUST support sending Binding Updates, as
as specified in Sections 6.3, 6.4, and 6.5; and MUST be able specified in Sections 8.3, 8.4, and 8.5; and MUST be able to
to receive and process Binding Acknowledgement messages, as receive and process Binding Acknowledgements, as specified in
specified in Section 6.7. Section 8.8.
- Every IPv6 mobile node MUST maintain a Binding Update List in - Every IPv6 mobile node MUST maintain a Binding Update List in
which it keeps track of which other IPv6 nodes it has sent a which it records the IP address of each other node to which it
Binding Update to, for which the Lifetime sent in that binding has sent a Binding Update, for which the Lifetime sent in that
has not yet expired. binding has not yet expired.
5. Binding Cache Management 6. Correspondent Node Operation
The Binding Cache is the central data structure in Mobile IPv6. A correspondent node is any node communicating with a mobile node.
All IPv6 nodes MUST support maintenance of a Binding Cache, and The correspondent node, itself, may be fixed or mobile, and may
MUST support processing of received Binding Updates. This section possibly also be functioning as a home agent for Mobile IPv6. The
describes the management aspects of a Binding Cache common to all procedures in this section thus apply to all IPv6 nodes.
nodes.
5.1. Receiving Binding Updates 6.1. 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 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 is
assumed to provide both authentication and integrity protection. assumed to provide both authentication and integrity protection.
- The length of the option specified in the Option Length field is - The Option Length field in the option is greater than or equal to
greater than or equal to 28 octets. 24 octets if the Home Link-Local Address (L) bit is not set, or
greater or equal to 40 octets if the Home Link-Local Address (L)
bit is set.
- The Identification field is valid. - The Identification field is valid.
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 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 differs from the Home Address, the specified Care-of Address is not equal to the Source Address
this is a request to cache a binding for the mobile node. in the IP header of the packet carrying the Binding Update,
Processing for this type of received Binding Update is described then this is a request to cache a binding for the mobile node
in Section 5.2. (the home address of the mobile node is specified by the Source
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 Home Address, then this is specified Care-of Address matches the Source Address field in the
a request to delete the mobile node's binding. Processing for IP header of the packet carrying the Binding Update, then this is
this type of received Binding Update is described in Section 5.3. a request to delete the mobile node's binding (as above, the home
address of the mobile node is specified by the Source Address
field in the packet's IP header). Processing for this type of
received Binding Update is described in Section 6.3.
5.2. Requests to Cache a Binding 6.2. 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 5.1, then the node binding for a mobile node, as specified in Section 6.1, 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 7.1.
If the Home Registration (H) bit is not set, then the receiving If the Home Registration (H) bit is not set, then the receiving node
node SHOULD create a new entry in its Binding Cache for this mobile SHOULD create a new entry in its Binding Cache for this mobile node
node's Home Address (or update its existing Binding Cache Entry for (or update its existing Binding Cache entry for this mobile node, if
this Home Address) to record the Care-of Address as specified in the such an entry already exists). The home address of the mobile node
Binding Update, and begin a timer to delete this Binding Cache entry is taken from the Source Address field in the packet's IP header.
The new Binding Cache entry records the association between this
address and the Care-of Address specified in the Binding Update.
The node must also begin a timer to delete this Binding Cache entry
after the expiration of the Lifetime period specified in the Binding after the expiration of the Lifetime period specified in the Binding
Update. Update.
5.3. Requests to Delete a Binding 6.3. 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 binding for a mobile node, as specified in Section 5.1, then the a binding for a mobile node, as specified in Section 6.1, then the
node MUST examine the Home Registration (H) bit in the Binding Update node 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 7.2. according to the procedure specified in Section 7.2.
If the Home Registration (H) bit is not set, and if a node receives a If the Home Registration (H) bit is not set, then the receiving node
valid Binding Update requesting it to delete a binding for a mobile MUST delete any existing entry in its Binding Cache for this mobile
node, as specified in Section 5.1, then it MUST delete any existing node. The home address of the mobile node is taken from the Source
entry in its Binding Cache for this mobile node's Home Address. Address field in the packet's IP header.
5.4. Sending Binding Acknowledgements 6.4. 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
it SHOULD return a Binding Acknowledgement message acknowledging in which the Acknowledge (A) bit is set, it SHOULD return a Binding
receipt of the Binding Update. If the node accepts the Binding Acknowledgement message acknowledging receipt of the Binding
Update and adds the binding contained in it to its Binding Cache, the Update. If the node accepts the Binding Update and adds the binding
Code field in the Binding Acknowledgement MUST be set to a value less contained in it to its Binding Cache, the Status field in the
than 128; if the node rejects the Binding Update and does not add Binding Acknowledgement MUST be set to a value less than 128; if
the binding contained in it to its Binding Cache, the Code field in the node rejects the Binding Update and does not add the binding
the Binding Acknowledgement MUST be set to a value greater than or contained in it to its Binding Cache, the Status field in the Binding
equal to 128. Specific values for the Code field are described in Acknowledgement MUST be set to a value greater than or equal to 128.
Section 3.2 and in the most recent "Assigned Numbers" [10].
The Destination Address in the IPv6 header for the Binding Specific values for the Status field are described in Section 4.2 and
Acknowledgement MUST be set to the Care-of Address copied from the in the most recent "Assigned Numbers" [12].
Binding Update option. This ensures that the Binding Acknowledgement
As described in Section 4.2, the packet in which the Binding
Acknowledgement is returned MUST include an IPv6 Authentication
header [1] in order to protect against forged Binding
Acknowledgements, and the packet MUST be sent using a Routing
header through the care-of address contained in the Binding Update
being acknowledged. This ensures that the Binding Acknowledgement
will be routed to the current location of the node sending the will be routed to the current location of the node sending the
Binding Update, whether the Binding Update was accepted or rejected. Binding Update, whether the Binding Update was accepted or rejected.
5.5. Cache Replacement Policy 6.5. 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 the Lifetime specified in the Binding Update from which expiration of the Lifetime specified in the Binding Update from which
the entry was created. Conceptually, a node MUST maintain a separate the entry was created or was last updated. Conceptually, a node
timer for each entry in its Binding Cache. When creating or updating maintains a separate timer for each entry in its Binding Cache. When
a Binding Cache entry in response to a received Binding Update, the creating or updating a Binding Cache entry in response to a received
node sets the timer for this entry to the specified Lifetime period. and accepted Binding Update, the node sets the timer for this entry
When a Binding Cache entry's timer expires, the node MUST delete the to the specified Lifetime period. When a Binding Cache entry's timer
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) SHOULD NOT be deleted from the cache registration" (Section 7.1) MUST NOT be deleted from the cache until
until the expiration of its lifetime period. When attempting to the expiration of its lifetime period. When attempting to add a new
add a new "home registration" entry in response to Binding Update "home registration" entry in response to a Binding Update with the
with the Home Registration (H) bit set, if insufficient space exists Home Registration (H) bit set, if insufficient space exists (or can
(or can be reclaimed) in the node's Binding Cache, the node MUST be reclaimed) in the node's Binding Cache, the node MUST reject the
reject the Binding Update and SHOULD return a Binding Acknowledgement Binding Update and SHOULD return a Binding Acknowledgement message
message to the sending mobile node, in which the Code field is set to to the sending mobile node, in which the Status field is set to 131
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 the 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 is
likely to work well. likely to work well.
If a packet is sent by a node to a destination for which it has If a packet is sent by a node to a destination for which it has
dropped the cache entry from its Binding Cache, the packet will be dropped the cache entry from its Binding Cache, the packet will be
routed normally, leading to the mobile node's home network, where it routed normally, leading to the mobile node's home subnet. There,
will be intercepted by the mobile node's home agent and tunneled to the packet will be intercepted by the mobile node's home agent and
the mobile node's current primary care-of address. As when a Binding tunneled to the mobile node's current primary care-of address. As
Cache entry is initially created, this indirect routing to the mobile when a Binding Cache entry is initially created, this indirect
node will result in the mobile node sending a Binding Update to this routing to the mobile node through its home agent will result in the
sending node, allowing it to add this entry again to its Binding mobile node sending a Binding Update to this sending node, allowing
this node to add an entry again for this destination to its Binding
Cache. Cache.
5.6. Receiving ICMP Error Messages 6.6. 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 node mobile node's address (its home address), then the correspondent
uses a Routing header to deliver the packet to the mobile node's node uses a Routing header to deliver the packet to the mobile node
care-of address, and then to the mobile node's home address. Any through the care-of address recorded in the Binding Cache entry. Any
ICMP error message caused by the packet on its way to the mobile node ICMP error message caused by the packet on its way to the mobile node
will be returned normally to the correspondent node. will 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 network, where it will be intercepted by the mobile node's home subnet, where it will be intercepted by the mobile node's
node's home agent, encapsulated, and tunneled to the mobile node's home agent, encapsulated, and tunneled to the mobile node's care-of
care-of address. Similarly, if a packet for a mobile node arrives address. Any ICMP error message caused by the packet on its way to
at the mobile node's previous default router (e.g., the mobile node the mobile node while in the tunnel, will be returned to the mobile
moved after the packet was sent), the router will encapsulate and node's home agent (the source of the tunnel) By the definition of
tunnel the packet to the mobile node's new care-of address (if it has IPv6 encapsulation [4], this encapsulating node MUST relay certain
a Binding Cache entry for the mobile node). Any ICMP error message ICMP error messages back to the original sender of the packet, which
caused by the packet on its way to the mobile node while in the in this case is the correspondent node.
tunnel, will be returned to the node that encapsulated the packet
(the home agent or the previous default router, respectively). By
the definition of IPv6 encapsulation [5], however, this encapsulating
node MUST relay certain ICMP error messages back to the original
sender of the packet (the correspondent node).
Thus, whether the correspondent node has a Binding Cache entry Likewise, if a packet for a mobile node arrives at the mobile node's
for the destination mobile node or not, the correspondent node previous default router (e.g., the mobile node moved after the packet
will receive any meaningful ICMP error message that is caused by was sent), the router will encapsulate and tunnel the packet to the
its packet on its way to the mobile node. If the correspondent mobile node's new care-of address (if it has a Binding Cache entry
node receives an ICMP Host Unreachable or Network Unreachable for the mobile node). As above, any ICMP error message caused by the
error message after sending a packet to a mobile node using its packet while in this tunnel will be returned to the previous default
cached care-of address, the correspondent node SHOULD delete its router (the source of the tunnel), which MUST relay certain ICMP
Binding Cache entry for this mobile node. If the correspondent node error messages back to the correspondent node [4].
subsequently transmits another packet to the mobile node, the packet
will be routed to the mobile node's home network, intercepted by the
mobile node's home agent, and tunneled to the mobile node's care-of
address using IPv6 encapsulation. The mobile node will then return a
Binding Update to the correspondent node, allowing it to recreate a
(correct) Binding Cache entry for the mobile node.
6. Mobile Node Considerations Thus, in all cases, any meaningful ICMP error messages caused by
packets from a correspondent node to a mobile node will be returned
to the correspondent node. If the correspondent node receives
persistent ICMP Host Unreachable or Network Unreachable error
messages after sending packets to a mobile node based on an entry in
its Binding Cache, the correspondent node SHOULD delete this Binding
Cache entry. If the correspondent node subsequently transmits
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
agent, and tunneled to the mobile node's care-of address using IPv6
encapsulation. The mobile node will then return a Binding Update to
the correspondent node, allowing it to recreate a (correct) Binding
Cache entry for the mobile node.
6.1. Movement Detection 6.7. Sending Packets to a Mobile Node
Before sending any packet, the sending node SHOULD examine its
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
for this address, the sending node SHOULD use a Routing header to
route the packet to this mobile node (the destination node) through
the care-of address recorded in that Binding Cache entry. For
example, assuming use of a Type 0 Routing header [5], if no other use
of a Routing header is involved in the routing of this packet, the
mobile node sets the following fields in the packet's IP header and
Routing header as indicated below:
- The Destination Address in the packet's IP header is set to the
mobile node's care-of address copied from the Binding Cache
entry.
- The Routing header is initialized to contain a single route
segment, with an Address of the mobile node's home address (the
original destination address to which the packet was being sent).
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
delivered to the mobile node (the mobile node has associated the
care-of address with its network interface). Normal processing of
the Routing header by the mobile node will then proceed as follows:
- The mobile node swaps the Destination Address in the packet's IP
header and the Address specified in the Routing header. This
results in the packet's IP Destination Address being set to the
mobile node's home address.
- The mobile node then resubmits the packet to its IPv6 module for
further processing. Since the mobile node recognizes its own
home address as one if its current IP addresses, the packet is
processed further within the mobile node, in the same way then as
if the mobile node was at home.
If, instead, the sending node has no Binding Cache entry for the
destination address to which the packet is being sent, the sending
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
is currently at home), the packet will be delivered directly to this
node and processed normally by it. If, however, the destination node
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
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
a Binding Update to the sending node, as described in Section 8.4,
allowing the sending node to create a Binding Cache entry for its use
in sending subsequent packets to this mobile node.
7. Home Agent Operation
7.1. Primary Care-of Address Registration
General processing of a received Binding Update that requests a
binding to be cached, is described in Section 6.2. However, if the
Home Registration (H) bit is set in the Binding Update, then the
receiving node MUST process the Binding Update as specified in this
section, rather than following the general procedure specified in
Section 6.2.
To begin processing the Binding Update, the home agent MUST perform
the following sequence of tests:
- If the node is not a router that implements home agent
functionality, then the node MUST reject the Binding Update and
SHOULD return a Binding Acknowledgement message to the mobile
node, in which the Status field is set to 132 (Home registration
not supported).
- Else, if the home address for the binding in the Binding Update
(the Source Address in the packet's IP header) is not an on-link
IPv6 address with respect to the home agent's current Prefix
List, then the home agent MUST reject the Binding Update and
SHOULD return a Binding Acknowledgement message to the mobile
node, in which the Status field is set to 133 (Not home subnet).
- Else, if the home agent chooses to reject the Binding Update for
any other reason (e.g., insufficient resources to serve another
mobile node as a home agent), then the home agent SHOULD return
a Binding Acknowledgement message to the mobile node, in which
the Status field is set to an appropriate value to indicate the
reason for the rejection.
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
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
home address, as described in Section 6.2. In addition, the home
agent MUST mark this Binding Cache entry as a "home registration"
to indicate that the node is serving as a home agent for this
binding. Binding Cache entries marked as a "home registration" MUST
be excluded from the normal cache replacement policy used for the
Binding Cache (Section 6.5) and MUST NOT be removed from the Binding
Cache until the expiration of the Lifetime period.
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
entry for this address marked as a "home registration"), then the
home agent MUST multicast onto the home subnet (to the all-nodes
multicast address) a Neighbor Advertisement message [8] on behalf
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
the Neighbor Advertisement message MUST be set to the mobile node's
home address, and the Advertisement MUST include a Target Link-layer
Address option specifying the home agent's link-layer address. The
Solicited Flag (S) in the Advertisement MUST NOT be set, since it was
not solicited by any Neighbor Solicitation message. The Override
Flag (O) in the Advertisement MUST be set, indicating that the
Advertisement SHOULD override any existing Neighbor Cache entry at
any node receiving it.
Any node on the home subnet receiving this Neighbor Advertisement
message will thus update its Neighbor Cache to associate the mobile
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
mobile node's home agent. Since multicasts on the local link (such
as Ethernet) are typically not guaranteed to be reliable, the home
agent MAY retransmit this Neighbor Advertisement message up to
MAX_ADVERT_REXMIT times to increase its reliability. It is still
possible that some nodes on the home subnet will not receive any of
these Neighbor Advertisements, but these nodes will eventually be
able to detect the link-layer address change for the mobile node's
home address, through use of Neighbor Unreachability Detection [8].
In addition, while this node is serving as a home agent to this
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 to reply to any received Neighbor Solicitation messages for it.
When a home agent receives a Neighbor Solicitation message, it MUST
check if the Target Address specified in the message matches the home
address of any mobile node for which it has a Binding Cache entry
marked as a "home registration". If such an entry exists in its
Binding Cache, the home agent MUST reply to the Neighbor Solicitation
message with a Neighbor Advertisement message, giving the home
agent's own link-layer address as the link-layer address for the
specified Target Address. Likewise, if the mobile node included its
home link-local address and set the Home Link-Local Address (L) bit
in its Binding Update with which it registered with its home agent,
its home agent MUST also similarly act as a proxy for the mobile
node's home link-local address while it has a "home registration"
entry in its Binding Cache for the mobile node. Acting as a proxy
in this way allows other nodes on the mobile node's home subnet to
resolve the mobile node's IPv6 home address and IPv6 link-local
address, and allows the home agent to to defend these addresses on
the home subnet for Duplicate Address Detection [8].
7.2. Primary Care-of Address De-registration
General processing of a received Binding Update that requests a
binding to be deleted, is described in Section 6.3. However, if the
Home Registration (H) bit is set in the Binding Update, then the
receiving node MUST process the Binding Update as specified in this
section, rather than following the general procedure specified in
Section 6.3.
To begin processing the Binding Update, the home agent MUST perform
the following sequence of tests:
- If the node is not a router that implements home agent
functionality, then the node MUST reject the Binding Update and
SHOULD return a Binding Acknowledgement message to the mobile
node, in which the Status field is set to 132 (Home registration
not supported).
- Else, if the home address for the binding in the Binding Update
(the Source Address in the packet's IP header) is not an on-link
IPv6 address with respect to the home agent's current Prefix
List, then it MUST reject the Binding Update and SHOULD return a
Binding Acknowledgement message to the mobile node, in which the
Status field is set to 133 (Not home subnet).
If the home agent does not reject the Binding Update as described
above, then it MUST delete any existing entry in its Binding Cache
for this mobile node.
In addition, the home agent MUST multicast a Neighbor Advertisement
message (to the all-nodes multicast address), giving the mobile
node's home address as the Target Address, and specifying the mobile
node's link-layer address in a Target Link-layer Address option in
the Neighbor Advertisement message. The home agent MAY retransmit
this Neighbor Advertisement message up to MAX_ADVERT_REXMIT times
to increase its reliability; any nodes on the home subnet that miss
all of these Neighbor Advertisements can also eventually detect the
link-layer address change for the mobile node's home address, through
use of Neighbor Unreachability Detection [8].
7.3. Tunneling Intercepted Packets to a Mobile Node
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,
the home agent is operating as a correspondent node of the mobile
node for this packet and the procedures described in Section 6.7
apply. The home agent uses a Routing header to route the packet
to the mobile node through the care-of address in the home agent's
Binding Cache (the mobile node's primary care-of address, in this
case).
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
any packets on the home subnet addressed to the mobile node's
home address, as described in Section 7.1. The home agent cannot
use a Routing header to forward these intercepted packets to the
mobile node, since it cannot modify the packet in flight without
invalidating any existing IPv6 Authentication header present in the
packet [1].
For forwarding each intercepted packet to the mobile node, the
home agent MUST tunnel the packet to the mobile node using IPv6
encapsulation [4]; the tunnel entry point node is the home agent,
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
home agent encapsulates an intercepted packet for forwarding to the
mobile node, the home agent sets the Source Address in the prepended
tunnel IP header to its own IP address, and sets the Destination
Address in the tunnel IP header to the mobile node's primary care-of
address. When received by the mobile node (using its primary care-of
address), normal processing of the tunnel header [4] will result in
decapsulation and processing of the original packet by the mobile
node.
7.4. Renumbering the Home Subnet
Neighbor Discovery [8] specifies a mechanism by which all nodes on a
subnet can gracefully autoconfigure new addresses, say by each node
combining a new routing prefix with its existing link-layer address.
As currently specified, this mechanism works when the nodes are on
the same link as the router issuing the necessary multicast packets
to advertise the new routing prefix(es) appropriate for the link.
However, for mobile nodes away from home, special care must be taken
to allow the mobile nodes to renumber gracefully. The most direct
method of ensuring this is for the home agent to encapsulate and
tunnel the multicast packets to the primary care-of address of each
mobile node for which it is serving as the home agent. The rules for
this are as follows:
- A mobile node assumes that its routing prefix has not changed
unless it receives authenticated Router Advertisement messages
from its home agent that the prefix has changed.
- When the mobile node is at home, the home agent does not tunnel
Router Advertisements to it.
- The mobile node's home agent serves as a proxy for the mobile
node's home address and link-local address, including defending
these addresses for Duplicate Address Detection, while the mobile
node is registered with the home agent away from home.
- When a home subnet prefix changes, the home agent tunnels Router
Advertisement packets to each mobile node which is currently
away from home and using a home address with the affected
routing prefix. Such tunneled Router Advertisements MUST be
authenticated [1].
- When a mobile node receives a tunneled Router Advertisement
containing a new routing prefix, it must perform the standard
autoconfiguration operation to create its new address
- When a mobile node returns to its home subnet, it must again
perform Duplicate Address Detection at the earliest possible
moment after it has registered with its home agent.
- A mobile node may send a Router Solicitation to its home agent at
any time, within the constraints imposed by rate control in the
Neighbor Discovery specification [8]
8. Mobile Node Operation
8.1. 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 IPv6 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 [9]. Neighbor Discovery [8].
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 [9]. Based on received messages, as specified for Router Discovery [8]. 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, router, and an entry in its Prefix List for each network prefix, that
that it currently considers to be on-link. Each entry in these it currently considers to be on-link. Each entry in these lists has
lists has an associated invalidation timer value (extracted from the 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 6.2. The mobile node registers prefixes is described in Section 8.2. 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 6.3. Section 8.3.
While away from home and using some router as its default router, While away from home and using some router as its default router,
it is important for a mobile node to be able to quickly detect when it is important for a mobile node to be able to quickly detect when
that router becomes unreachable, so that it can switch to a new that router becomes unreachable, so that it can switch to a new
default router and to a new primary care-of address. Since some default router and to a new primary care-of address. Since some
links (notably wireless) do not necessarily work equally well in links (notably wireless) do not necessarily work equally well in both
both directions, it is likewise important for the mobile node to directions, it is likewise important for the mobile node to detect
detect when it becomes unreachable to its default router, so that any when it becomes unreachable to its default router, so that the mobile
correspondent nodes attempting to communicate with the mobile node node can take steps to ensure that any correspondent nodes attempting
can still reach it. to communicate with the it can 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 node SHOULD use Neighbor Unreachability Detection. As specified in
in Neighbor Discovery [9], while the mobile node is actively Neighbor Discovery [8], while the mobile node is actively sending
sending packets to (or through) its default router, the mobile node packets to (or through) its default router, the mobile node can
can detect that the router has become unreachable either through detect that the router is still reachable either through indications
indications from upper layer protocols on the mobile node that a from upper layer protocols on the mobile node that a connection is
connection is not making "forward progress" (e.g., TCP timing out making "forward progress" (e.g., receipt of TCP acknowledgements for
waiting for an acknowledgement after a number of retransmissions), new data transmitted), or through receipt of a Neighbor Advertisement
or through the failure to receive a Neighbor Advertisement messages message form its default router in response to an explicit Neighbor
form its default router in response to retransmitted explicit Solicitation messages to it. Note that although this mechanism only
Neighbor Solicitation messages to it. No exceptions to Neighbor detects that the mobile node's default router has become unreachable
Unreachability Detection are necessary for this aspect of movement to the mobile node while the mobile node is actively sending packets
detection in Mobile IPv6. to it, this is the only time that this direction of reachability
confirmation is needed. Confirmation that the mobile node is still
reachable from the router is handled separately, as described below.
For a mobile node to detect when it has become unreachable to its For a mobile node to detect when it has become unreachable to its
default router, however, the mobile node cannot efficiently rely on default router, however, the mobile node cannot efficiently rely on
Neighbor Unreachability Detection alone, since the network overhead Neighbor Unreachability Detection alone, since the network overhead
would be prohibitively high in many cases for a mobile node to would be prohibitively high in many cases for a mobile node to
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 IPv6 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 to its default router,
even in the absence of other packets to it from the router. On some even in the absence of other packets to it from the router. On some
types of network interfaces, the mobile node MAY also supplement types of network interfaces, the mobile node MAY also supplement this
this by setting its network interface into "promiscuous" receive by setting its network interface into "promiscuous" receive mode,
mode, so that is able to receive all packets on the link, including so that it is able to receive all packets on the link, including
those not link-level addressed to it. The mobile node will then those not link-level addressed to it. The mobile node will then
be able to detect any packets sent by the router, in order to to 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 form 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 Unreachability Detection probes above, and thus, such extra Neighbor Solicitation probes should
should rarely be necessary. rarely be necessary.
With some types of networks, it is possible that additional With some types of networks, it is possible that additional
indications about link-layer mobility can be obtained from indications about link-layer mobility can be obtained from
lower-layer protocol or device driver software within the mobile lower-layer protocol or device driver software within the mobile
node. However, a mobile node MUST NOT assume that all link-layer node. However, a mobile node MUST NOT assume that all link-layer
mobility indications from lower layers indicate a movement of the mobility indications from lower layers indicate a movement of the
mobile node's link-layer connection to a new IPv6 subnet, such that mobile node's link-layer connection to a new IP subnet, such that the
the mobile node would need to switch to a new default router and mobile node would need to switch to a new default router and primary
primary care-of address. Upon lower-layer indication of link-layer care-of address. Upon lower-layer indication of link-layer mobility,
mobility, the mobile node SHOULD send Router Solicitation messages the mobile node SHOULD send Router Solicitation messages to determine
to determine if new routers (and new on-link network prefixes) are if new routers (and new on-link network prefixes) are present on its
present on its new link. new link.
Such lower-layer information might also be useful to a mobile node in Such lower-layer information might also be useful to a mobile node in
deciding to switch its primary care-of address to one of the other deciding to switch its primary care-of address to one of the other
care-of addresses it has formed from the on-link network prefixes care-of addresses it has formed from the on-link network prefixes
currently available through different default routers from which the currently available through different default routers from which the
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.
6.2. Forming New Care-of Addresses 8.2. 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 (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 a time (registered with its home agent), but it MAY have an at a time (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 each network prefix on its current
link. Furthermore, since a wireless network interface may actually link. Furthermore, since a wireless network interface may actually
allow a mobile node to be reachable on more than one link at a time allow a mobile node to be reachable on more than one link at a time
(i.e., within wireless transmitter range of routers on more than one (i.e., within wireless transmitter range of routers on more than one
separate link), a mobile node MAY have care-of addresses on more than separate link), a mobile node MAY have care-of addresses on more than
one link at a time. For more information on using more than one one link at a time. The use of more than one care-of address at a
care-of address at a time, see Section 6.8. time is described in Section 8.9.
As described in Section 2, in order to form a new care-of address, As described in Section 3, in order to form a new care-of address,
a mobile node MAY use either stateless [12] or stateful (e.g., a mobile node MAY use either stateless [14] 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, it send packets as part of the method of address autoconfiguration,
MUST use an IPv6 link-local address rather than its own IPv6 home it MUST use an IPv6 link-local address rather than its own IPv6
address as the Source Address. home address as the Source Address in the IP header of each such
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 while visiting this address that has been assigned to it for its use only while visiting
network. For example, it may be statically configured with an IPv6 a specific foreign subnet. For example, a mobile node may be
address assigned by the system administrator of the new network. If statically configured with an IPv6 address assigned by the system
so, rather than using address autoconfiguration to form a new care-of administrator of some foreign subnet, for its use while visiting that
address using this network prefix, the mobile node SHOULD use its own subnet. If so, rather than using address autoconfiguration to form
pre-assigned address as its care-of address on this network. 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
this subnet.
6.3. Sending Binding Updates to the Home Agent 8.3. Sending Binding Updates to the Home Agent
After changing its primary care-of address as described in After deciding to change its primary care-of address as described
Sections 6.1 and 6.2, a mobile node SHOULD register its new primary in Sections 8.1 and 8.2, a mobile node MUST register this care-of
care-of address with its home agent. To do so, the mobile node sends address with its home agent in order to make this its primary care-of
a packet to its home agent containing a Binding Update option with address. To do so, the mobile node sends a packet to its home agent
the Acknowledge (A) bit set, requesting the home agent to return a containing a Binding Update option with the Home Registration (H)
Binding Acknowledgement message in response to this Binding Update. bit is set in the Binding Update. The mobile node also sets the
As described in Section 3.2, the mobile node SHOULD retransmit this Acknowledge (A) bit in the Binding Update, requesting the home
Binding Update to its home agent until it receives a matching Binding agent to return a Binding Acknowledgement message in response to
Acknowledgement message. Once reaching a retransmission timeout this Binding Update. As described in Section 4.2, the mobile node
period of MAX_BINDACK_TIMEOUT, the mobile node SHOULD continue SHOULD retransmit this Binding Update to its home agent until it
to periodically retransmit the Binding Update at this rate until receives a matching Binding Acknowledgement message. Once reaching a
acknowledged. 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).
It is useful for a mobile node to be able to send a Binding Update 8.4. Sending Binding Updates to Correspondent Nodes
its home agent without explicitly knowing the home agent's address.
For example, since the mobile node was last at home, it may have
become necessary to replace the node serving as its home agent due
to the failure of the original node or due to reconfiguration of the
home network. It thus may not always be possible or convenient for a
mobile node to know the exact address of its own home agent.
Mobile nodes can dynamically discover the address of a home agent A mobile node MAY send a Binding Update to any correspondent node at
by sending a Binding Update to the anycast address on their home any time (subject to the rate limiting defined in Section 8.7). In
network. Each router on the home network which receives this Binding any Binding Update sent by a mobile node, the Care-of Address field
Update MUST reject the Binding Update and include its address in the MUST be set to one of the care-of addresses currently in use by the
Binding Acknowledgement message indicating the rejection. The mobile mobile node or to the mobile node's home address. If set to one of
node is assumed to know a proper anycast address on its home network the mobile node's current care-of addresses (the care-of address
before making use of this method for determining a particular home given MAY differ from the mobile node's primary care-of address), the
agent's address. Binding Update requests the correspondent node to create or update
a an entry for the mobile node in the correspondent node's Binding
Cache to record this care-of address for use in sending future
packets to the mobile node. If, instead, the Care-of Address field
is set to the mobile node's home address, the Binding Update requests
the correspondent node to delete any existing Binding Cache entry
that it has for the mobile node. A mobile node MAY set the Care-of
Address field differently for sending Binding Updates to different
correspondent nodes.
6.4. Sending Binding Updates to Correspondent Nodes When sending any Binding Update, the mobile node MUST record in its
Binding Update List the following fields from the Binding Update:
A mobile node MAY also include a Binding Update in any normal data - The IP address of the node to which the Binding Update was sent.
packet sent to a correspondent node. For each correspondent node
to which it has sent a Binding Update, the mobile node MUST keep - The home address for which the Binding Update was sent,
information to determine whether or not the correspondent node has
been sent a fresh Binding Update since the last time the mobile node - The remaining lifetime of the binding, initialized from the
switched to a new primary care-of address. When a packet is to be Lifetime field of the Binding Update.
sent to a correspondent node that has not been sent a fresh Binding
Update, the mobile node SHOULD include the Binding Update within the The mobile node MUST retain in its Binding Update List information
packet. Thus, correspondent nodes are generally kept updated and about all Binding Updates sent, for which the lifetime of the
can send almost all data packets directly to the mobile node using binding has not yet expired. When sending a Binding Update, if an
the mobile node's current binding. Such Binding Updates are not entry already exists in the mobile node's Binding Update List for
generally required to be acknowledged; however, if the mobile node an earlier Binding Update sent to that same destination node, the
wants to be sure, an acknowledgement can be requested, although in existing Binding Update List is updated to reflect the new Binding
this case, the mobile node SHOULD NOT continue to retransmit the Update rather than creating a new Binding Update List entry.
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
Section 8.3), the mobile node will also typically send a Binding
Update to each correspondent node for which an entry exists in the
mobile node's Binding Update List. Thus, correspondent nodes are
generally kept updated and can send almost all packets directly to
the mobile node using the mobile node's current binding.
The mobile node, however, need not send these Binding Updates
immediately after configuring a new care-of address. For example,
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
sending a new Binding Update to any correspondent node for a
short period of time, in hopes that the needed Binding Update
can be included in some packet that the mobile node sends to that
correspondent node for some other reason (for example, as part of
some TCP connection in use). In this case, when sending a packet
to some correspondent node, the mobile node SHOULD check in its
Binding Update List to determine if a new Binding Update to this
correspondent node is needed, and SHOULD include the new Binding
Update in this packet as necessary.
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
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
care-of address in its Binding Cache entry for the mobile node, the
mobile node SHOULD return a Binding Update to the sender giving its
current care-of address. In particular, the mobile node SHOULD
return a Binding Update in response to receiving a packet that meets
all of the following tests:
- The packet was tunneled using IPv6 encapsulation.
- The Destination Address in the tunnel (outer) IP header is equal
to any of the mobile node's care-of addresses.
- The Destination Address in the original (inner) IP header is
equal to the mobile node's home address. If the original packet
contains a Routing header, the final Address indicated in the
Routing header should be used in this comparison rather than the
Destination Address in the original IP header.
- The Source Address in the tunnel (outer) IP header differs from
the Source Address in the original (inner) IP header.
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
Source Address in the original (inner) IP header of the packet.
Binding Updates sent to correspondent nodes are not generally
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
node's Binding Cache, the mobile node MAY request an acknowledgement
by setting the Acknowledge (A) bit in the Binding Update. In this
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 also send a Binding Update in any otherwise empty
packet, whenever the mobile node wishes to update a correspondent
node as to its current binding. This is normally done only if
the mobile suspects that its home agent is not operational or is
too far away, a correspondent node is not sending the traffic to
the proper care-of address, or there is an immediate need for the
correspondent node to obtain the binding. A mobile node can detect
that a correspondent node is not sending packets to the proper
care-of address because in that case the packets arrive at the mobile
node's care-of address by encapsulation instead by inclusion in a
routing header within the packet.
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 3.1. 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.
6.5. Sending Binding Updates to the Previous Default Router 8.5. 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 primary care-of address), a mobile node SHOULD send a Binding its primary care-of address), a mobile node SHOULD send a Binding
Update message to its previous default router, giving its new care-of Update message to its previous default router, giving its new care-of
address. If it sends such a Binding Update, the mobile node MUST set address. If the mobile node sends such a Binding Update, the Source
the Home Address field to its old primary care-of address (that it Address in the packet carrying this Binding Update MUST be set the
used while using this default router), and set the Care-of Address mobile node's old primary care-of address (that it used while using
field to its new primary care-of address. Note that the previous this default router), and the Care-of Address field MUST be set to
router does not necessarily know the mobile node's home address as the mobile node's new primary care-of address. In addition, the Home
part of this sequence of events. Registration (H) bit MUST also be set in this Binding Update, to
request the mobile node's previous default router to temporarily act
as a home agent for the mobile node's old primary care-of address.
Note that the previous router does not necessarily know the mobile
node's home address as part of this sequence of events.
The mobile node's previous default router then, in effect, If any subsequent packets arrive at this previous router for
temporarily act as a home agent for the mobile node's old primary forwarding to the mobile node's old primary care-of address,
care-of address. If any subsequent packets arrive at this previous the router SHOULD encapsulate each such packet (using IPv6
router for forwarding to the mobile node's old primary care-of encapsulation [4]) and tunnel it to the mobile node at its new
address, the router SHOULD encapsulate each and tunnel it to the primary care-of address. Moreover, for the lifetime of the "home
mobile node at its new primary care-of address. Moreover, the registration" Binding Cache entry at this router, this router MUST
previous router should issue Neighbor Advertisement packets for the act as a proxy for the mobile node's previous care-of address,
previous care-of address, so that on-link neighbors will send packets for purposes of participation in Neighbor Discovery [8], in the
destined to the mobile node's old primary care-of address to the same way as any home agent does for a mobile node's home address
previous router for encapsulation and tunneling to its new care-of (Section 7.1). This allows the router to intercept packets addressed
address. to the mobile node's previous care-of address, and to encapsulate and
tunnel them to the mobile node's new care-of address, as described in
Section 7.3.
6.6. Rate Limiting for Sending Binding Updates 8.6. Retransmitting Binding Updates
A mobile node MUST NOT send Binding Update messages more often than If, after sending a Binding Update in which the Acknowledge (A)
once per MAX_UPDATE_RATE seconds to any correspondent node. After bit is set, a mobile node fails to receive an acceptable Binding
sending 5 consecutive Binding Updates to a particular correspondent Acknowledgement within INITIAL_BINDACK_TIMEOUT seconds, the
node with the same care-of address, the mobile node SHOULD reduce its mobile node SHOULD retransmit the Binding Update until a Binding
rate of sending Binding Updates to that correspondent node, to the Acknowledgement is received. Such a retransmitted Binding
rate of SLOW_UPDATE_RATE per second. The mobile node MAY continue Update MUST use he same Identification value as the original
to send Binding Updates at the slower rate indefinitely, in hopes transmission. The retransmissions by the mobile node MUST use
that the correspondent node will finally be able to process a Binding an exponential back-off process, in which timeout period is
doubled upon each retransmission until either the node receives a
Binding Acknowledgement or the timeout period reaches the value
MAX_BINDACK_TIMEOUT.
8.7. Rate Limiting for Sending Binding Updates
A mobile node MUST NOT send Binding Updates more often than once per
MAX_UPDATE_RATE seconds to any correspondent node. After sending 5
consecutive Binding Updates to a particular correspondent node with
the same care-of address, the mobile node SHOULD reduce its rate
of sending Binding Updates to that correspondent node, to the rate
of SLOW_UPDATE_RATE per second. The mobile node MAY continue to
send Binding Updates at the slower rate indefinitely, in hopes that
the correspondent node will eventually be able to process a Binding
Update and begin to route its packets directly to the mobile node at Update and begin to route its packets directly to the mobile node at
its current primary care-of address. its new care-of address.
6.7. Receiving Binding Acknowledgements 8.8. Receiving Binding Acknowledgements
Upon receiving a packet carrying a Binding Acknowledgement message, Upon receiving a packet carrying a Binding Acknowledgement, a mobile
a mobile node MUST validate the packet according to the following node MUST validate the packet according to the following tests:
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 is
assumed to provide both authentication and integrity protection. assumed to provide both authentication and integrity protection.
- The ICMP Checksum is valid. - The Option Length field in the option is greater than or equal to
8 octets.
- The length of the ICMP message (derived from the IPv6 Payload
Length field) is greater than or equal to 16 octets.
- The Identification field is valid. - The Identification field is valid.
Any Binding Acknowledgement not satisfying all of these tests MUST be Any Binding Acknowledgement not satisfying all of these tests MUST be
silently discarded. silently ignored, although the remainder of the packet (i.e., other
options, extension headers, or payload) SHOULD be processed normally
according to any procedure defined for that part of the packet.
If the Binding Acknowledgement is valid, the mobile node MUST examine When a mobile node receives a packet carrying a valid Binding
the Code field as follows: Acknowledgement, the mobile node MUST examine the Status field as
follows:
- If the Code field indicates that the Binding Update was accepted - If the Status field indicates that the Binding Update was
(the Code field is less than 128), then the mobile node MUST accepted (the Status field is less than 128), then the mobile
update the corresponding entry in its Binding Update List to node MUST update the corresponding entry in its Binding Update
indicate that the Binding Update has been acknowledged. The List to indicate that the Binding Update has been acknowledged.
mobile node SHOULD thus stop retransmitting the Binding Update. The mobile node MUST thus stop retransmitting the Binding Update.
- If the Code field indicates that the Binding Update was not - If the Status field indicates that the Binding Update was not
accepted (the Code 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. Optionally, the mobile node MAY take steps to correct the
cause of the error and retransmit the Binding Update, subject to cause of the error and retransmit the Binding Update, subject to
the rate limiting restriction specified in Section 6.6. the rate limiting restriction specified in Section 8.7.
6.8. Using Multiple Care-of Addresses 8.9. Using Multiple Care-of Addresses
As described in Section 6.2, a mobile node MAY have more than As described in Section 8.2, a mobile node MAY have more than
one care-of address at a time. Particularly in the case of many one care-of address at a time. Particularly in the case of many
wireless networks, a mobile node effectively may be reachable through wireless networks, a mobile node effectively may be reachable
multiple link-level points of attachment at the same time (e.g., through multiple link-level points of attachment at the same time
with overlapping wireless cells), on which different on-link network (e.g., with overlapping wireless cells), on which different on-link
prefixes may exist. A mobile node SHOULD select a primary care-of network prefixes may exist. A mobile node SHOULD select a primary
address from among those care-of addresses it has formed using any care-of address from among those care-of addresses it has formed
of these network prefixes, based on the movement detection mechanism using any of these network prefixes, based on the movement detection
in use (Section 6.1). When the mobile node selects a new primary mechanism in use (Section 8.1). When the mobile node selects a new
care-of address, it MUST register it with its home agent through a primary care-of address, it MUST register it with its home agent
Binding Update message with the Acknowledge (A) bit set, as described through a Binding Update message with the Home Registration (H) and
in Section 6.3. Acknowledge (A) bits set, as described in Section 8.3.
To assist in smooth handoffs, a mobile node SHOULD retain its To assist with smooth handoffs, a mobile node SHOULD retain
previous primary care-of address as a care-of address, and SHOULD its previous primary care-of address as a (non-primary) care-of
still accept packets at this address, even after registering its new address, and SHOULD still accept packets at this address, even after
primary care-of address with its home agent. This is reasonable, registering its new primary care-of address with its home agent.
since the mobile node could only receive packets at its previous This is reasonable, since the mobile node could only receive packets
primary care-of address if it were indeed still connected to that at its previous primary care-of address if it were indeed still
link. If the previous primary care-of address was allocated using connected to that link. If the previous primary care-of address
stateful address autoconfiguration [3], the mobile node may not wish was allocated using stateful address autoconfiguration [3], the
to release the address immediately upon switching to a new primary mobile node may not wish to release the address immediately upon
care-of address. The stateful address autoconfiguration server switching to a new primary care-of address. The stateful address
will allow mobile nodes to acquire new addresses while still using autoconfiguration server will allow mobile nodes to acquire new
previously allocated addresses. addresses while still using previously allocated addresses.
6.9. Returning Home 8.10. Returning Home
A mobile node detects that it has returned to its home network A mobile node detects that it has returned to its home subnet through
through the movement detection algorithm in use (Section 6.1), the movement detection algorithm in use (Section 8.1), when the
when the mobile node detects that its home network prefix is again mobile node detects that the network prefix of its home subnet is
on-link. The mobile node SHOULD then send a Binding Update to its again on-link. The mobile node SHOULD then send a Binding Update to
home agent, to instruct its home agent to no longer intercept or its home agent, to instruct its home agent to no longer intercept
tunnel packets for it. In this Binding Update, the mobile node MUST or tunnel packets for it. In this Binding Update, the mobile node
set the Care-of Address field to its own IPv6 home address. As with MUST set the Care-of Address field to its own IPv6 home address. As
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 message is received.
The mobile node MUST also send out the appropriate Neighbor In addition, the mobile node MUST multicast onto the home subnet
Advertisement packets with the Override flag set, so that its (to the all-nodes multicast address) a Neighbor Advertisement
neighbors on its home network will update the relevant information message [8], to advertise its link-layer address for its own IPv6
for the mobile node in their Neighbor Caches. The mobile node home address. The Target Address in this Neighbor Advertisement
MUST do this for both its link-local address and its home address. message MUST be set to the mobile node's home address, and the
The Neighbor Advertisement packets can be repeated a small number Advertisement MUST include a Target Link-layer Address option
of times to guard against occasional loss of packets on the home specifying the mobile node's link-layer address. Similarly, the
network. mobile node MUST multicast a Neighbor Advertisement message to
advertise its link-layer address for its IPv6 link-local address.
7. Home Agent Considerations The Solicited Flag (S) in these Advertisements MUST NOT be set, since
they were not solicited by any Neighbor Solicitation message. The
7.1. Home Agent Care-of Address Registration Override Flag (O) in these Advertisements MUST be set, indicating
that the Advertisements SHOULD override any existing Neighbor Cache
General processing of a received Binding Update that requests a entries at any node receiving them.
binding to be cached, is described in Section 5.2. However, if the
Home Registration (H) bit is set in the Binding Update, then the
receiving node MUST process the Binding Update as specified in this
section, rather than following the generall procedure specified in
Section 5.2.
To begin processing the Binding Update, the home agent MUST perform
the following sequence of tests:
- If the node is not a router that implements home agent
functionality, then the node MUST reject the Binding Update and
SHOULD return a Binding Acknowledgement message to the mobile
node, in which the Code field is set to 132 (Home registration
not supported).
- Else, if the Home Address field in the Binding Update is not an
on-link IPv6 address with respect to the home agent's current
Prefix List, then the home agent MUST reject the Binding Update
and SHOULD return a Binding Acknowledgement message to the mobile
node, in which the Code field is set to 133 (Not home network).
- Else, if the home agent chooses to reject the Binding Update for
any other reason (e.g., insufficient resources to serve another
mobile node as a home agent), then the home agent SHOULD return a
Binding Acknowledgement message to the mobile node, in which the
Code field is set to an appropriate value to indicate the reason
for the rejection.
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 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 Home Address, as described in Section 5.2. In
addition, the home agent MUST mark this Binding Cache entry as a
"home registration" to indicate that the node is serving as a home
agent for this binding. Binding Cache entries marked as a "home
registration" SHOULD be excluded from the normal cache replacement
policy used for the Binding Cache (Section 5.5) and SHOULD NOT be
removed from the Binding Cache until the expiration of the Lifetime
period.
If the home agent was not already serving as a home agent for the
Home Address specified in the Binding Update (the home agent did
not already have a Binding Cache entry for this address marked as
a "home registration"), then the home agent MUST multicast onto
the home network (to the all-nodes multicast address), a Neighbor
Advertisement message on behalf of the mobile node, with the fields
in the Neighbor Advertisement set as follows:
Router Flag (R)
1 -- the sending node (the home agent) is a router.
Solicited Flag (S)
0 -- the Neighbor Advertisement message is unsolicited.
Override Flag (O)
1 -- the advertisement SHOULD override any existing Neighbor
Cache entry at the receiver, updating the receiver's cached
link-layer address for this Target Address.
Target Address
The mobile node's home address, copied from the Home Address
field of the Binding Update.
Options
The home agent MUST include at least a Target Link-layer
Address option in the Neighbor Advertisement message, in which
the Link-Layer Address gives the link-layer address of the home
agent itself.
Any node on the home network receiving this Neighbor Advertisement
message will thus update its Neighbor Cache to associate the mobile
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
mobile node's home agent. Since multicasts on the local link (such
as Ethernet) are typically not guaranteed to be reliable, the home
agent MAY retransmit this Neighbor Advertisement message a small
number of times to increase its reliability. It is still possible
that some nodes on the home network will not receive any of these
Neighbor Advertisements, but these nodes will eventually be able
to detect the link-layer address change for the mobile node's home
address, through use of Neighbor Unreachability Detection [9].
In addition, while this node is serving as a home agent to any mobile
node (it has at least one entry marked as a "home registration" in
its Binding Cache), it SHOULD act as a proxy for each such mobile
node to reply to any received Neighbor Solicitation messages for
it. When a home agent receives a Neighbor Solicitation message, it
MUST check if the Target Address specified in the message matches
the Home Address of any mobile node for which it has a Binding Cache
entry marked as a "home registration". If such an entry exists
in its Binding Cache, the home agent MUST reply to the Neighbor
Solicitation message with a Neighbor Advertisement message, giving
the home agent's own link-layer address as the link-layer address for
the specified Target Address.
7.2. Home Agent Care-of Address De-registration
General processing of a received Binding Update that requests a
binding to be deleted, is described in Section 5.3. However, if the
Home Registration (H) bit is set in the Binding Update, then the
receiving node MUST process the Binding Update as specified in this
section, rather than following the generall procedure specified in
Section 5.3.
To begin processing the Binding Update, the home agent MUST perform
the following sequence of tests:
- If the node is not a router that implements home agent
functionality, then the node MUST reject the Binding Update and
SHOULD return a Binding Acknowledgement message to the mobile
node, in which the Code field is set to 132 (Home registration
not supported).
- Else, if the Home Address field in the Binding Update is not an
on-link IPv6 address with respect to the home agent's current
Prefix List, then it MUST reject the Binding Update and SHOULD
return a Binding Acknowledgement message to the mobile node, in
which the Code field is set to 133 (Not home network).
If the home agent does not reject the Binding Update as described
above, then it MUST delete any existing entry in its Binding Cache
for this mobile node's Home Address, as specified in the Binding
Update.
In addition, the home agent SHOULD multicast a Neighbor Advertisement
message (to the all-nodes multicast address), giving the mobile
node's home address as the Target Address, and specifying the mobile
node's link-layer address in a Target Link-layer Address option in
the Neighbor Advertisement message. The home agent MAY retransmit
this Neighbor Advertisement message a small number of times to
increase its reliability, and any nodes on the home network that miss
all of these Neighbor Advertisements can also eventually detect the
link-layer address change for the mobile node's home address, through
use of Neighbor Unreachability Detection [9].
7.3. Delivering Packets to a Mobile Node
Home agents cannot use Routing headers to deliver packets to the
mobile node, because they can't modify the packet and add to it
in flight. They must always use IPv6 encapsulation [5] for this
purpose.
When a home agent encapsulates a packet for delivery to the mobile
node, the home agent uses the care-of address as the destination
address in the outer IPv6 header. Since the mobile node is presumed
to be receiving packets at the care-of address, the delivery path
from the care-of address to the mobile node's home address is then
trivial.
Note that the home agent cannot insert a routing header, or
modify the destination address of the mobile node, because of IPv6
authentication mechanisms [1]. The home agent is expected to be
involved only rarely with the transmission of data to the mobile
node, because the mobile node will send Binding Updates as soon as
possible to its correspondent nodes.
7.4. Renumbering the Home Network
Neighbor Discovery [9] specifies a mechanism by which all nodes on a
network can gracefully autoconfigure new addresses, say by combining
a new routing prefix with their existing MAC address. As currently
specified, this mechanism works when the nodes are on the same link
as the router issuing the necessary multicast packets to advertise
the new routing prefix(es) appropriate for the link.
However, for mobile nodes away from home, special care must be taken
to allow the mobile nodes to renumber gracefully. The most direct
method of insuring this is for the home agent to encapsulated and
tunnel the multicast packets to the care-of address of the mobile
node as necessary. The rules for this are as follows:
- A mobile node assumes that its routing prefix has not changes
unless it receives authenticated router advertisement messages
from its home agent that the prefix has changed.
- When the mobile node is at home, the home agent does not tunnel
router advertisements to it.
- When a home network prefix changes, the home agent tunnels router
advertisement packets to each mobile node which is currently
away from home and using a home address with the affected
routing prefix. Such tunneled router advertisements MUST be
authenticated [1].
- When a mobile node receives a tunneled router advertisement
containing a new routing prefix, it must perform the standard
autoconfiguration operation to create its new address
- When a mobile node returns to its home network, it must again
perform Duplicate Address Detection at the earliest possible
moment after it has registered with its home agent.
- A mobile node may send a router solicitation to its home agent at
any time, within the constraints imposed by rate control in the
Neighbor Discovery specification [9]
Note that a mobile node is guaranteed that its home address is unique
and used by no other mobile node. However, in some circumstances it
may nevertheless be true that other nodes on its home network form
the same link-local address as the mobile node during the time when
the mobile node is away from its home network. Thus, there is the
requirement above that the mobile node perform Duplicate Address
Detection when it returns again to its home network.
8. Correspondent Node Considerations
8.1. Delivering Packets to a Mobile Node
The routing infrastructure of the Internet will normally route a
packet destined to a mobile node to the mobile node's home network,
if the Destination Address in the packet's IPv6 header is the mobile
node's home address. Once the packet reaches the home network, it
will be intercepted by the mobile node's home agent if the mobile
node is away from home, and will then be encapsulated using IPv6
encapsulation and tunneled to the mobile node's current primary
care-of address. Using this delivery mechanism, the sender need not
know that the node is mobile.
Correspondent nodes that have received and cached a Binding Update
for a mobile node, MAY instead route packets directly to that mobile
node's care-of address. To do so, the correspondent node includes
a Routing header in each packet to the mobile node, to cause the
packet to be routed to the mobile node's care-of address as the last
intermediate routing point before reaching the final destination
of the mobile node's home address. When the packet arrives at the
care-of address (which the mobile node has associated with its
network interface), normal processing of the Routing header by the
mobile node will result in delivery of the packet to the mobile node
as the final destination of the packet.
For example, assuming no other use of the Routing header in the
packet, the sender initializes the Destination Address in the IPv6
header to the mobile node's care-of address, and includes a Type 0
Routing header [6] in the packet initialized as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type=0|Segments Left=1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Strict/Loose Bit Map |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Home Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header
8-bit selector. Identifies the type of header immediately
following the Routing header.
Hdr Ext Len
8-bit unsigned integer. Length of the Routing header in
8-octet units, not including the first 8 octets. For this use
of the Type 0 Routing header, Hdr Ext Len is equal to 2.
Routing Type
0
Segments Left
8-bit unsigned integer. Number of route segments remaining
before reaching the final destination. For this use of the
Type 0 Routing header, Segments Left is initialized to 1 by the
sender.
Reserved
8-bit reserved field. Initialized to zero for transmission;
ignored on reception.
Strict/Loose Bit Map
24-bit bit-map, numbered 0 to 23, left-to-right. For this use
of the Type 0 Routing header, bit 0 of the Strict/Loose Bit Map
is set to 1, indicating strict routing from the care-of
address to the mobile node's home address (both addresses are
associated with the mobile node itself).
Home Address
The home address of the destination mobile node.
If a correspondent node receives an ICMP Host Unreachable or Network
Unreachable message after sending a packet to a mobile node using
its cached care-of address, it SHOULD delete the cache entry from
its Binding Cache until information about the mobile node's current
care-of address becomes available (via a Binding Update).
9. Authentication and Replay Protection
When sending Binding Updates, a mobile node uses the Identification Since multicasts on the local link (such as Ethernet) are typically
field in the option, in conjunction with the IPv6 Authentication not guaranteed to be reliable, the mobile node MAY retransmit
Header, to protect against replays of the Binding Update. The style these Neighbor Advertisement messages up to MAX_ADVERT_REXMIT times
of replay protection specified for the IPv6 Binding Update involves to increase their reliability. It is still possible that some
the use of a timestamp as the Identification data. Accordingly the nodes on the home subnet will not receive any of these Neighbor
mobile node and the target of its Binding Update have to roughly Advertisements, but these nodes will eventually be able to recover
agree on the current time. Stale Binding Updates MUST be rejected. through use of Neighbor Unreachability Detection [8].
10. Routing Multicast Packets 9. Routing Multicast Packets
A mobile node that is connected to its home network functions just A mobile node that is connected to its home subnet functions in the
like any other (stationary) node. Thus, when it is at home, a mobile same way as any other (stationary) node. Thus, when it is at home,
node functions identically to other multicast senders and receivers. a mobile node functions identically to other multicast senders and
This section therefore describes the behavior of a mobile node that receivers. This section therefore describes the behavior of a mobile
is not on its home network. node that is not on its home subnet.
In order receive multicasts, a mobile node must join the multicast In order receive packets sent to some multicast group, a mobile node
group. Mobile nodes MAY join multicast groups in order to receive must join the that multicast group. One method by which a mobile
transmissions in one of two ways. First, they MAY join the group node MAY join the group is via a (local) multicast router on the
via a (local) multicast router on the visited subnet. This option foreign subnet being visited. This option assumes that there is a
assumes that there is a multicast router present on the visited multicast router present on the foreign subnet. The mobile node
subnet. The mobile node SHOULD use its dynamically acquired care-of SHOULD use its care-of address sharing a network prefix with the
address (if it has acquired one) as the source IPv6 address of its multicast router, as the source IPv6 address of its multicast group
multicast group membership control message packets. Otherwise, it membership control message packets.
MAY use its home address.
Alternatively, a mobile node which wishes to receive multicasts can Alternatively, a mobile node MAY join multicast groups via a
join groups via a bi-directional tunnel to its home agent, assuming bi-directional tunnel to its home agent, assuming that its home agent
that its home agent is a multicast router. The mobile node tunnels is a multicast router. The mobile node tunnels the appropriate
the appropriate multicast group membership control packets to its multicast group membership control packets to its home agent, and the
home agent and the home agent forwards multicast packets down the home agent forwards multicast packets down the tunnel to the mobile
tunnel to the mobile node. The home agent must tunnel the packet node. The home agent MUST tunnel the packet directly to the mobile
directly to the mobile node's dynamically acquired care-of address, node's primary care-of address.
or, the packet must be tunneled first to the mobile node's home
address and then recursively tunneled to the mobile node's care-of
address.
A mobile node which wishes to send packets to a multicast group also A mobile node that wishes to send packets to a multicast group
has two options: (1) send directly on the visited network; or (2) also has two options: (1) send directly on the foreign subnet
send via a tunnel to its home agent. Because multicast routing in being visited; or (2) send via a tunnel to its home agent. Because
general depends upon the IPv6 source address, a mobile node which multicast routing in general depends upon the Source Address used
sends multicast packets directly on the visited network MUST use a in the IP header of the multicast packet, a mobile node that sends
dynamically acquired care-of address as the IPv6 source address. multicast packets directly on the foreign subnet MUST use its
Similarly, a mobile node which tunnels a multicast packet to its home care-of address as the IPv6 Source Address of each multicast packet.
agent MUST use its home address as the IPv6 source address of both 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
the (inner) multicast packet and the (outer) encapsulating packet. the (inner) multicast packet and the (outer) encapsulating packet.
This second option assumes that the home agent is a multicast router. This second option assumes that the home agent is a multicast router.
11. 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 1 per second MAX_UPDATE_RATE once per second
SLOW_UPDATE_RATE once per 10 seconds SLOW_UPDATE_RATE once per 10 seconds
Acknowledgements MAX_ADVERT_REXMIT 3
We would like to thank Thomas Narten for contributing valuable
discussion and reviewing this draft, and for helping to shape some of
the recent changes relevant to the operation of Neighbor Discovery.
References
[1] R. Atkinson. IP Authentication Header. RFC 1826, August 1995.
[2] R. Atkinson. Security Architecture for the Internet Protocol.
RFC 1825, August 1995.
[3] J. Bound and C. Perkins. Dynamic Host Configuration Protocol
for IPv6. draft-ietf-dhc-dhcpv6-05.txt -- work in progress,
June 1996.
[4] A. Conta and S. Deering. Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6). RFC 1885,
December 1995.
[5] A. Conta and S. Deering. Generic Packet Tunneling in IPv6.
draft-ietf-ipngwg-ipv6-tunnel-01.txt - work in progress,
February 1996.
[6] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6)
Specification. RFC 1883, December 1995.
[7] D. Haskin and E. Allen. IP Version 6 over PPP. 11. Security Considerations
draft-ietf-ipngwg-pppext-ipv6cp-03.txt - work in progress, June
1996.
[8] David B. Johnson and Charles E. Perkins. Route Optimization The Binding Update option described in this document will result
in Mobile-IP. draft-ietf-mobileip-optim-04.txt -- work in in packets addressed to a mobile node being delivered instead to
progress, February 1996. its care-of address. This ability to change the routing of these
packets could be a significant vulnerability if any packet containing
a Binding Update option was not authenticated. Such use of "remote
redirection", for instance as performed by the Binding Update option,
is widely understood to be a security problem in the current Internet
if not authenticated [2].
[9] T. Narten, E. Nordmark, and W. Simpson. IPv6 Neighbor The mobile computing environment is potentially very different from
Discovery. draft-ietf-ipngwg-discovery-03.txt -- work in the ordinary computing environment. In many cases, mobile computers
progress, November 1995. will be connected to the network via wireless links. Such links
are particularly vulnerable to passive eavesdropping, active replay
attacks, and other active attacks.
[10] Joyce K. Reynolds and Jon Postel. Assigned Numbers. RFC 1700, Users who have sensitive data that they do not wish others to see
October 1994. should use mechanisms outside the scope of this document (such as
encryption) to provide appropriate protection. Users concerned about
traffic analysis should consider appropriate use of link encryption.
If absolute location privacy is desired, the mobile node can create a
tunnel to its home agent. Then, packets destined for correspondent
nodes will appear to emanate from the home subnet, and it may be
more difficult to pinpoint the location of the mobile node. Such
mechanisms are all beyond the scope of this document.
[11] Fumio Teraoka. draft-teraoka-ipv6-mobility-sup-02.txt. Acknowledgements
Internet Draft -- work in progress, January 1996.
[12] S. Thomson and T. Narten. IPv6 Stateless Address We would like to thank the members of the Mobile IP and IPng Working
Autoconfiguration. draft-ietf-addrconf-ipv6-auto-06.txt Groups for their comments and suggestions on this draft. We would
- work in progress, November 1995. 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. Open Issues
A.1. Session Keys with Local Routers A.1. Session Keys with Local Routers
In the IPv4 route optimization proposal [8], a mechanism is outlined In the IPv4 route optimization proposal [7], a mechanism is outlined
whereby a session key can be established between foreign agents whereby a session key can be established between foreign agents
and mobile nodes, without requiring any pre-established security and mobile nodes, without requiring any pre-established security
relationship between them. A similar mechanism could be defined for relationship between them. A similar mechanism could be defined for
IPv6, to avoid the need for a possibly time-consuming negotiation IPv6, to avoid the need for a possibly time-consuming negotiation
between routers and mobile nodes for the purpose of obtaining the between routers and mobile nodes for the purpose of obtaining the
session key, which under many circumstances would only be used once. session key, which under many circumstances would only be used once.
This mechanism, if needed, can be specified completely outside This mechanism, if needed, can be specified completely outside
the Mobile IPv6 protocol and would amount to a way of creating a the Mobile IPv6 protocol and would amount to a way of creating a
dynamic security association between two nodes which do not share an dynamic security association between two nodes which do not share an
existing trust relationship, but which need to agree on a key for existing trust relationship, but which need to agree on a key for
skipping to change at page 40, line 34 skipping to change at page 45, line 34
A.2. Source Address Filtering by Firewalls A.2. Source Address Filtering by Firewalls
The current specification does nothing to permit mobile nodes to The current specification does nothing to permit mobile nodes to
send their packets through firewalls which filter out packets with send their packets through firewalls which filter out packets with
the "wrong" source IPv6 addresses in the IPv6 packet header. The the "wrong" source IPv6 addresses in the IPv6 packet header. The
mobile node's home address may be unlikely to fall within the ranges mobile node's home address may be unlikely to fall within the ranges
required to satisfy the firewall's criteria for further delivery. required to satisfy the firewall's criteria for further delivery.
As indicated by recent discussion, firewalls are unlikely to As indicated by recent discussion, firewalls are unlikely to
disappear. Any standardized solution [11] to the firewall problem disappear. Any standardized solution [13] to the firewall problem
based on hiding the non-local source address outside the source based on hiding the non-local source address outside the source
address field of the IPv6 header is likely to fail. Any vendor or address field of the IP header is likely to fail. Any vendor or
facilities administrator wanting to filter based on the address in facilities administrator wanting to filter based on the address in
the IPv6 source address field would also quickly begin filtering on the IPv6 source address field would also quickly begin filtering on
hidden source addresses. hidden source addresses.
Assume, for the moment, that a mobile node is able to establish a Assume, for the moment, that a mobile node is able to establish a
secure tunnel through a firewall protecting the domain in which secure tunnel through a firewall protecting the domain in which
a correspondent node is located. The mobile node could then a correspondent node is located. The mobile node could then
encapsulate its packet so that the outer IPv6 header was addressed 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 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 source address. When the firewall decapsulates, it would be able to
authenticate the inner packet based (correctly) on the mobile node's authenticate the inner packet based (correctly) on the mobile node's
home address. After the authentication is performed, the firewall home address. After the authentication is performed, the firewall
could forward the packet to the correspondent node as desired. This could forward the packet to the correspondent node as desired. This
simple procedure has the feature that it requires the minimal amount simple procedure has the feature that it requires the minimal amount
of encapsulation, no assistance by routers or other agents, and that of encapsulation, no assistance by routers or other agents, and that
the firewall can establish a security relationship with the mobile the firewall can establish a security relationship with the mobile
node based on its home (i.e., permanent) address. node based on its home (i.e., permanent) address.
A.3. Dynamic Home Agent Address Discovery
It is useful for a mobile node to be able to send a Binding Update
its home agent without explicitly knowing the home agent's address.
For example, since the mobile node was last at home, it may have
become necessary to replace the node serving as its home agent due
to the failure of the original node or due to reconfiguration of the
home subnet. It thus may not always be possible or convenient for a
mobile node to know the exact address of its own home agent. Several
methods of allowing a mobile node to dynamically discover the address
of a router in its home subnet are currently under consideration.
A.4. Replay Protection for Binding Updates
Some transforms for use in conjunction with the IP Authentication
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
Acknowledgement) is currently specified in this document for use
in sequencing Binding Updates at the receiver, and in matching
returned Binding Acknowledgements with outstanding Binding Updates
at the sender. The use of this field in this manner, together with
the use of the current IP Authentication transforms that supports
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
[1] Randall Atkinson. IP Authentication header. RFC 1826, August
1995.
[2] S. M. Bellovin. Security problems in the TCP/IP protocol suite.
ACM Computer Communications Review, 19(2), March 1989.
[3] Jim Bound and Charles Perkins. Dynamic Host Configuration
Protocol for IPv6 (DHCPv6). Internet-Draft,
draft-ietf-dhc-dhcpv6-07.txt, August 1996. Work in progress.
[4] Alex Conta and Stephen Deering. Generic packet
tunneling in IPv6 specification. Internet-Draft,
draft-ietf-ipngwg-ipv6-tunnel-02.txt, June 1996. Work
in progress.
[5] Stephen E. Deering and Robert M. Hinden. Internet Protocol
version 6 (IPv6) specification. RFC 1883, December 1995.
[6] Shu jen Chang and Robert Glenn. HMAC-SHA IP authentication with
replay prevention. Internet-Draft,
draft-ietf-ipsec-ah-hmac-sha-04.txt, November 1996. Work in
progress.
[7] David B. Johnson and Charles Perkins. Route optimization in
Mobile IP. Internet-Draft, draft-ietf-mobileip-optim-04.txt,
February 1996. Work in progress.
[8] Thomas Narten, Erik Nordmark, and William Allen Simpson.
Neighbor Discovery for IP version 6 (IPv6). RFC 1970, August
1996.
[9] Michael J. Oehler and Robert Glenn. HMAC-MD5 IP
authentication with replay prevention. Internet-Draft,
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] J. B. Postel, editor. Transmission Control Protocol. RFC 793,
September 1981.
[12] Joyce K. Reynolds and Jon Postel. Assigned numbers. RFC 1700,
October 1994.
[13] Fumio Teraoka. Mobility support in IPv6. Internet-Draft,
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.
Chair's Address Chair's Address
The Working Group can be contacted via its current chair: 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
USA
Work: +1-847-576-2753 Phone: +1 847 576-2753
E-mail: solomon@comm.mot.com E-mail: solomon@comm.mot.com
Erik Nordmark
Sun Microsystems, Inc.
2550 Garcia Avenue
Mt. View, CA 94041
USA
Phone: +1 415 786-5166
Fax: +1 415 786-5896
E-mail: nordmark@sun.com
Authors' Addresses Authors' Addresses
Questions about this document can also be directed to the authors: Questions about this document can also be directed to the authors:
David B. Johnson David B. Johnson
Computer Science Department
Carnegie Mellon University Carnegie Mellon University
Computer Science Department
5000 Forbes Avenue 5000 Forbes Avenue
Pittsburgh, PA 15213-3891 Pittsburgh, PA 15213-3891
USA
Work: +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
Room H3-D34
T. J. Watson Research Center
IBM Corporation IBM Corporation
T. J. Watson Research Center
Room H3-D34
30 Saw Mill River Rd. 30 Saw Mill River Rd.
Hawthorne, NY 10532 Hawthorne, NY 10532
USA
Work: +1 914 789-7350 Phone: +1 914 789-7350
Fax: +1 914 784-6205 Fax: +1 914 784-6205
E-mail: perk@watson.ibm.com E-mail: perk@watson.ibm.com
 End of changes. 

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