Network Working Group David B. Johnson
INTERNET DRAFT Carnegie Mellon University
15 March 1995 Charles Perkins
IBM Corporation
Andrew Myles
Macquarie University
Route Optimization in Mobile IP
draft-ietf-mobileip-optim-01.txt
Abstract
This document defines extensions to the operation of the basic
Mobile IP protocol to allow for optimization of datagram routing from
a correspondent node to a mobile node. Without Route Optimization,
all datagrams destined to a mobile node are routed through that
mobile node's home agent, which then tunnels each datagram to the
mobile node's current location. The protocol extensions described
here provide a means for correspondent nodes that implement them to
cache the location of a mobile node and to then tunnel their own
datagrams for the mobile node directly to that location, bypassing
the possibly lengthy route for each datagram to and from the mobile
node's home agent. Extensions are also provided to allow datagrams
in flight when a mobile node moves, and datagrams sent based on an
out-of-date cached location, to be forwarded directly to the mobile
node's new location.
Status of This Memo
This document is a product of the Mobile IP Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to working group mailing list at mobile-ip@tadpole.com. Distribution
of this memo is unlimited.
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at
any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress".
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To learn the current status of any Internet-Draft, please check
the "1id-abstracts.txt" listing contained in the Internet- Drafts
Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).
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Contents
Abstract i
Status of This Memo i
1. Introduction 1
2. Route Optimization Overview 3
2.1. Location Caching . . . . . . . . . . . . . . . . . . . . 3
2.2. Foreign Agent Handoff . . . . . . . . . . . . . . . . . . 3
2.3. Location Cache Updates . . . . . . . . . . . . . . . . . 6
3. Route Optimization Message Formats 8
3.1. Binding Warning Message . . . . . . . . . . . . . . . . . 9
3.2. Binding Request Message . . . . . . . . . . . . . . . . . 10
3.3. Binding Update Message . . . . . . . . . . . . . . . . . 11
3.4. Binding Acknowledge Message . . . . . . . . . . . . . . . 13
4. Route Optimization Extension Formats 14
4.1. Previous Foreign Agent Notification Extension . . . . . . 15
4.2. Route Optimization Authentication Extension . . . . . . . 17
4.3. Registration Key Request Extension . . . . . . . . . . . 18
4.4. Mobile Node Registration Key Extension . . . . . . . . . 19
4.5. Foreign Agent Registration Key Extension . . . . . . . . 20
4.6. Foreign Agent Public Key Extension . . . . . . . . . . . 21
5. Mobility Security Association Management 22
5.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 22
5.2. Mobility Security Associations . . . . . . . . . . . . . 23
6. Location Cache Considerations 24
6.1. Cache Management . . . . . . . . . . . . . . . . . . . . 24
6.2. Receiving Binding Warning Messages . . . . . . . . . . . 24
6.3. Receiving Binding Update Messages . . . . . . . . . . . . 25
6.4. Using Special Tunnels . . . . . . . . . . . . . . . . . . 25
7. Home Agent Considerations 26
7.1. Rate Limiting . . . . . . . . . . . . . . . . . . . . . . 26
7.2. Receiving Binding Request Messages . . . . . . . . . . . 26
7.3. Receiving Registration Key requests . . . . . . . . . . . 27
7.4. Receiving Special Tunnels . . . . . . . . . . . . . . . . 27
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8. Foreign Agent Considerations 28
8.1. Setting up Temporary Mobility Security Associations . . . 28
8.2. Previous Foreign Agent Notification . . . . . . . . . . . 29
8.3. Receiving Tunneled Datagrams . . . . . . . . . . . . . . 30
8.4. Sending Special Tunnels . . . . . . . . . . . . . . . . . 30
9. Mobile Node Considerations 31
9.1. Requesting a Registration Key . . . . . . . . . . . . . . 31
9.2. Notifying Previous Foreign Agents . . . . . . . . . . . . 31
References 33
Appendix A. Using a Master Key at the Home Agent 34
Chairs' Addresses 35
Authors' Addresses 36
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1. Introduction
The basic Mobile IP protocol [3] allows any mobile node to move
about, changing its point of attachment to the Internet, while
continuing to be addressed by its home IP address. Correspondent
nodes sending IP datagrams to a mobile node address them to the
mobile node's home address in the same way as to any destination.
While the mobile node is connected to the Internet away from its
home network, it is served by a "home agent" on its home network
and is associated with a "care-of address" indicating its current
location. The association between a mobile node's home address and
its care-of address is known as a "mobility binding". The care-of
address is generally the address of a "foreign agent" on the network
being visited by the mobile node, which forwards arriving datagrams
locally to the mobile node. Alternatively, the care-of address may
be temporarily assigned to the mobile node using DHCP [1] or other
means. All IP datagrams addressed to the mobile node are routed by
the normal IP routing mechanisms to the mobile node's home network,
where they are intercepted by the mobile node's home agent, which
then tunnels each datagram to the mobile node's current care-of
address. Datagrams sent by a mobile node use the foreign agent as a
default router but require no other special handling or routing.
This basic scheme allows transparent interoperation with mobile
nodes, but forces all datagrams for a mobile node to be routed
through its home agent; packets to the mobile node are often routed
along paths that are significantly longer than optimal. For example,
if a mobile node, say MN1, is visiting some subnet, even datagrams
from a correspondent node on this same subnet must be routed through
the Internet to MN1's home agent on MN1's home network, only to then
be tunneled back to the original subnet to MN1's foreign agent for
delivery to MN1. This indirect routing can significantly delay the
delivery of the datagram to MN1 and places an unnecessary burden on
the networks and routers along this path through the Internet. If
the correspondent node in this example is actually another mobile
node, say MN2, then datagrams from MN1 to MN2 must likewise be routed
through MN2's home agent on MN2's home network and back to the
original subnet for delivery to MN1.
This document defines extensions to the basic Mobile IP protocol to
allow for the optimization of datagram routing from a correspondent
node to a mobile node. These extensions provide a means for nodes
that implement them to cache the care-of address of a mobile node
and to then tunnel their own datagrams directly there, bypassing the
possibly lengthy route to and from that mobile node's home agent.
Extensions are also provided to allow datagrams in flight when a
mobile node moves, and datagrams sent based on an out-of-date cached
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care-of address, to be forwarded directly to the mobile node's new
care-of address. These extensions are collectively referred to as
Route Optimization in this document.
All operation of Route Optimization that changes the routing of IP
datagrams to the mobile node is authenticated using the same type of
authentication mechanism used in the basic Mobile IP protocol. This
authentication generally relies on a "mobility security association"
established in advance between the node sending a message and the
node receiving the message that must authenticate it. When the
required mobility security association has not been established, a
Mobile IP implementation using Route Optimization operates in the
same way as the basic Mobile IP protocol.
Section 2 of this document provides an overview of the operation of
Route Optimization. Section 3 defines the message types used by
Route Optimization, and Section 4 defines the message extensions
used. Section 5 discusses the problem of managing the mobility
security associations needed to provide authentication of all
messages that affect the routing of datagrams to a mobile node.
The final four sections of this document define in detail the
operation of Route Optimization from the point of view of each of the
entities involved: considerations for nodes maintaining a location
cache are presented in Section 6, mobile node considerations in
Section 9, foreign agent considerations in Section 8, and home agent
considerations in Section 7.
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2. Route Optimization Overview
2.1. Location Caching
Route Optimization provides a means for any node that wishes to
optimize its own communication with mobile nodes to maintain a
"location cache" containing the mobility binding of one or more
mobile nodes. When sending an IP datagram to a mobile node, if the
sender has a location cache entry for the destination mobile node, it
may tunnel the datagram directly to the care-of address indicated in
the cached mobility binding.
In the absence of any location cache entry, datagrams destined for
a mobile node will be routed to the mobile node's home network in
the same way as any other IP datagram, and are then tunneled to the
mobile node's current care-of address by the mobile node's home
agent. This is the only routing mechanism supported by the basic
Mobile IP protocol. With Route Optimization, as a side effect of
this indirect routing of a datagram to a mobile node, the original
sender of the datagram may be informed of the mobile node's current
mobility binding, giving the sender an opportunity to cache the
binding.
A node may create a location cache entry for a mobile node only when
it has received and authenticated the mobile node's mobility binding.
Likewise, a node may update an existing location cache entry for a
mobile node, such as after the mobile node has moved to a new foreign
agent, only when it has received and authenticated the mobile node's
new mobility binding.
A location cache will, by necessity, have a finite size. Any node
implementing a location cache may manage the space in its cache
using any local cache replacement policy. If a datagram is sent
to a destination for which the cache entry has been dropped from
the cache, the datagram will be routed normally through the mobile
node's home network and will be tunneled to the mobile node's care-of
address by its home agent. This indirect routing to the mobile node
will result in the original sender of the datagram being informed of
the mobile node's current mobility binding, allowing it to add this
entry again to its location cache.
2.2. Foreign Agent Handoff
When a mobile node moves and registers with a new foreign agent, the
basic Mobile IP protocol does not notify the mobile node's previous
foreign agent. IP datagrams intercepted by the home agent after
the new registration are tunneled to the mobile node's new care-of
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address, but datagrams in flight that had already been intercepted
by the home agent and tunneled to the old care-of address when the
mobile node moved are lost and are assumed to be retransmitted by
higher-level protocols if neeeded. The old foreign agent eventually
deletes the mobile node's registration after the expiration of the
lifetime period established when the mobile node registered there.
Route Optimization provides a means for the mobile node's previous
foreign agent to be reliably notified of the mobile node's new
mobility binding, allowing datagrams in flight to the mobile
node's previous foreign agent to be forwarded to its new care-of
address. This notification also allows any datagrams tunneled to the
mobile node's previous foreign agent from correspondent nodes with
out-of-date location cache entries for the mobile node (that have not
yet learned that the mobile node has moved), to be forwarded to its
new care-of address. Finally, this notification allows any resources
consumed by the mobile node's binding at the previous foreign agent
(such as radio channel reservations) to be released immediately,
rather than waiting for the mobile node's registration to expire.
During registration with a new foreign agent, the mobile node and the
new foreign agent may establish a "registration key", which acts as a
session key for this registration. When a Registration Key Request
extension is included in the Registration Request message to the
mobile node's home agent, the home agent may choose a registration
key and include it in its Registration Reply message. The home agent
includes a Mobile Node Registration Key extension, containing a copy
of the chosen key encrypted under a key and algorithm shared between
the home agent and the mobile node, and a Foreign Agent Registration
Key extension, containing a copy of the same key encrypted under
a key and algorithm shared between the home agent and the foreign
agent. In order for the registration key to be established, the
foreign agent must have a mobility security association with the home
agent. This security association may either be preestablished or may
be established for purposes of this registration through exchange of
the foreign agent's public encryption key in the Agent Advertisement
and Registration Request messages. The registration key for a mobile
node can be stored by the foreign agent with the mobile node's
visitor list entry.
When a mobile node registers with a new foreign agent, if it
established a registration key during registration with its previous
foreign agent, it may use this key to notify the previous foreign
agent that it has moved. This notification may also optionally
include the mobile node's new care-of address, allowing the previous
foreign agent to create a location cache entry for the mobile node to
serve as a "forwarding pointer" to its new location. Any tunneled
datagrams for the mobile node that arrive at this previous foreign
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agent after this location cache entry has been created will then be
re-tunneled by this foreign agent to the mobile node's new location
using the mobility binding in this location cache entry. The
registration key is used to authenticate the notification sent to the
previous foreign agent.
As part of the registration procedure, the mobile node may
request that its new foreign agent attempt to notify its previous
foreign agent on its behalf, by including a Previous Foreign Agent
Notification extension in its Registration Request message sent to
the new foreign agent. The new foreign agent then builds a Binding
Update message and transmits it to the mobile node's previous foreign
agent as part of registration, requesting an acknowledgement from
the previous foreign agent. The Previous Foreign Agent Notification
extension includes only those values needed to construct the Binding
Update message that are not already contained in the Registration
Request message. The authenticator for the Binding Update message is
computed by the mobile node based on its registration key shared with
its previous foreign agent.
The mobile node is responsible for occasionally retransmitting a
Binding Update message to its previous foreign agent until the
matching Binding Acknowledge message is received, or until the mobile
node can be sure of the expiration of its registration with that
foreign agent.
The location cache entry created at the mobile node's previous
foreign agent is treated in the same way as any other location cache
entry. In particular, it is possible that this location cache
entry will be deleted from the cache at any time. In this case,
the foreign agent will be unable to re-tunnel subsequently arriving
tunneled datagrams for the mobile node directly to its new location.
Suppose a node (for instance, such a previous foreign agent) receives
a datagram that has been tunneled to this node, but this node is
unable to deliver the datagram locally to the destination mobile node
(the node is not the mobile node itself, and it is not a foreign
agent with a visitor list entry for the mobile node). To attempt
delivery of the datagram in this case, the node must encapsulate
the datagram as a "special tunnel" datagram (Section 8.4), destined
to the mobile node. Otherwise, the datagram would eventually reach
the mobile node's home network, be intercepted by the mobile node's
home agent, and be tunneled to the mobile node's current care-of
address. If the home agent were to tunnel the datagram back to the
same foreign agent, a loop would be created.
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2.3. Location Cache Updates
When a mobile node's home agent intercepts a datagram from the home
network and tunnels it to the mobile node, the home agent may deduce
that the original sender of the datagram has no location cache entry
for the destination mobile node. In this case, the home agent MAY
send a Binding Update message to the sender, informing it of the
mobile node's current mobility binding. No acknowledgement for this
Binding Update message is needed, since additional future datagrams
from this sender intercepted by the home agent for the mobile node
will cause transmission of another update. In order for this Binding
Update to be authenticated by the sender of the datagram, the home
agent and the sender must have established a mobility security
association.
Similarly, when any node receives a tunneled datagram tunneled
to this node, if it is not the current foreign agent serving the
destination as a mobile node the source of the tunneled datagram
probably has an out-of-date location cache entry for the destination
mobile node. In this case, this node MAY send a Binding Warning
message to the originator of the tunneled datagram. As above, no
acknowledgement of this Binding Warning is needed.
Unlike the Binding Update message, though, no authentication of the
Binding Warning message is necessary, since it does not directly
affect the routing of IP datagrams to the mobile node. Instead, when
a node receives a Binding Warning message, that node sends a Binding
Request message to the indicated mobile node's home agent, requesting
the mobile node's current mobility binding. The home agent then
answers this Binding Request message with a Binding Update message,
and when the Binding Update message is received, the node may then
create a location cache entry for the mobile node. In order for this
node and the home agent to exchange these Binding Request and Binding
Update messages, they must have established a mobility security
association.
Each Binding Update message indicates the maximum lifetime of any
location cache entry created from the Binding Update. When sending
the Binding Update message, the home agent SHOULD set this lifetime
to the remaining service lifetime associated with the mobile node's
current registration. Any location cache entry established or
updated in response to this Binding Update message must be marked
to be deleted after the expiration of this period. A node wanting
to provide continued service with a particular location cache entry
may attempt to reconfirm that mobility binding before the expiration
of this lifetime period. Location cache entry reconfirmation
may be appropriate when the node has indications (such as an open
transport-level connection to the mobile node) that the location
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cache entry is still needed. This reconfirmation is performed by
the node sending a Binding Request message to the mobile node's home
agent, requesting it to reply with the mobile node's current mobility
binding in a new Binding Update message.
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3. Route Optimization Message Formats
Route Optimization defines four message types used for management
of location cache entries. Each of these messages begins with a
one-octet field indicating the type of the message.
The following Type codes are defined in this document:
16 = Binding Warning message
17 = Binding Request message
18 = Binding Update message
19 = Binding Acknowledge message
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3.1. Binding Warning Message
A Binding Warning message is used to advise a node that it appears
to have either no location cache entry or an out-of-date location
cache entry for some mobile node. When any node receives a datagram
tunneled to itself, if it is not the current foreign agent for the
destination mobile node, it MAY send a Binding Warning message to the
node that originated the tunneled datagram.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mobile Node Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
16
Reserved
Sent as 0; ignored on reception.
Mobile Node Home Address
The home address of the mobile node to which the Binding
Warning message refers.
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3.2. Binding Request Message
A Binding Request message is used by a node to request a mobile
node's current mobility binding from the mobile node's home agent.
It is sent by a node upon receiving a Binding Warning message, or by
a node desiring to update the mobility binding in a location cache
entry that it holds for the mobile node.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mobile Node Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
17
Reserved
Sent as 0; ignored on reception.
Mobile Node Home Address
The home address of the mobile node to which the Binding
Request refers.
Identification
A 64-bit sequence number, assigned by the node sending the
Binding Request message, used to assist in matching requests
with replies, and in protecting against replay attacks.
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3.3. Binding Update Message
The Binding Update message is used to notify another node of a mobile
node's current mobility binding. It MAY be sent by the mobile node's
home agent in response to a Binding Request message. It MAY also
be sent by a mobile node, or by the foreign agent with which the
mobile node is registering, when notifying the mobile node's previous
foreign agent that the mobile node has moved.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |A|I| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mobile Node Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Care-of Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
+-+-+-+-+-+-+-+-
Type
18
Acknowledge (A)
The Acknowledge (A) bit is set by the node sending the Binding
Update message to request a Binding Acknowledge message be
returned acknowledging its receipt.
Identification Present (I)
The (I) bit is set by the node sending the Binding Update
message to indicate whether or not the Identification field is
present.
Reserved
Sent as 0; ignored on reception.
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Lifetime
The number of seconds remaining before the location cache entry
must be considered expired. A value of all ones indicates
infinity. A value of zero indicates that no location cache
entry for the mobile node should be created, and any existing
location cache entry (and visitor list entry, in the case of
a mobile node's previous foreign agent) for the mobile node
should be deleted. The lifetime is typically equal to the
remaining lifetime of the mobile node's registration.
Mobile Node Home Address
The home address of the mobile node to which the Binding Update
message refers.
Care-of Address
The current care-of address of the mobile node. When set equal
to the home address of the mobile node, the Binding Update
message instead indicates that no location cache entry for the
mobile node should be created, and any existing location cache
entry (and visitor list entry, in the case of a mobile node's
previous foreign agent) for the mobile node should be deleted.
Identification
If present, a 64-bit number, assigned by the node sending the
Binding Request message, used to assist in matching requests
with replies, and in protecting against replay attacks.
The Route Optimization Authentication extension (Section 4.2) is
required.
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3.4. Binding Acknowledge Message
A Binding Acknowledge message is used to acknowledge receipt of a
Binding Update message. It is sent by a node receiving the Binding
Update message, if the Acknowledge (A) bit is set in the Binding
Update message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |N| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mobile Node Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
19
N
This bit is set if the acknowledgement is negative. For
instance, if the binding update was not accepted, but the
incoming datagram has the Acknowledge flag set, then the N bit
is set in this Binding Acknowledge message.
DISCUSSION: Alternatively, we could replace this bit with a
status code, as in the Registration Reply message. The mobile
node could log the error, but currently has no real way to
recover from it.
Reserved
Sent as 0; ignored on reception.
Mobile Node Home Address
Copied from the Binding Update message being acknowledged.
Identification
Copied from the Binding Update message being acknowledged, if
present there.
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4. Route Optimization Extension Formats
Route Optimization defines the following Mobile IP message
extensions:
96 = Previous Foreign Agent Notification extension
97 = Route Optimization Authentication extension
98 = Registration Key Request extension
99 = Mobile Node Registration Key extension
100 = Foreign Agent Registration Key extension
101 = Foreign Agent Public Key extension
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4.1. Previous Foreign Agent Notification Extension
The Previous Foreign Agent Notification Extension may be included in
a Registration Request message sent to a foreign agent. It requests
the new foreign agent to send a Binding Update message on behalf of
the mobile node, to the mobile node's previous foreign agent, to
notify it that the mobile node has moved. The previous foreign agent
deletes the mobile node's visitor list entry and creates a location
cache entry for the mobile node pointing to its new care-of address.
The extension contains only those values not otherwise already
contained in the Registration Request message, which are needed for
the new foreign agent to construct the Binding Update message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Cache Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Previous Foreign Agent Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authenticator ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
96
Length
6 plus the length of the Authenticator
Cache Lifetime
The number of seconds remaining before the location cache
entry created by the previous foreign agent must be considered
expired. A value of all ones indicates infinity. A value
of zero indicates that the previous foreign agent should not
create a location cache entry for the mobile node once it
has deleted the mobile node's visitor list entry. The Cache
Lifetime value is copied into the Lifetime field of the Binding
Update message.
Previous Foreign Agent Address
The IP address of the mobile node's previous foreign agent
to which the new foreign agent should send a Binding Update
message on behalf of the mobile node.
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Authenticator
The authenticator value to be used in the Route Optimization
Authentication extension in the Binding Update message sent by
the new foreign agent to the mobile node's previous foreign
agent. This authenticator is calculated only over the Binding
Update message body.
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4.2. Route Optimization Authentication Extension
The Route Optimization Authentication Extension is used to
authenticate certain Route Optimization management messages.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Authenticator ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
97
Length
The length of the Authenticator
Authenticator
(variable length) A hash value taken over a stream of bytes
including the shared secret, all prior extensions in their
entirety, the the Route Optimization management data, and
the type and length of this extension, but not including the
Authenticator field itself.
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4.3. Registration Key Request Extension
The Registration Key Request extension may be used on Registration
Request messages to request a registration key from the mobile
node's home agent. The extension is authenticated along with the
rest of the Registration Request message, and thus no additional
authenticator is included in the extension. In response to a
Registration Key Request extension, the home agent MAY include
a Mobile Node Registration Key extension and a Foreign Agent
Registration Key extension in its Registration Reply message,
containing encrypted copies of the registration key for the mobile
node the foreign agent.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Foreign Agent Public Key ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
98
Length
The length of the Foreign Agent Public Key, or 0 if no Foreign
Agent Public Key is present
Foreign Agent Public Key
If the mobile node received a Foreign Agent Public Key
extension in the foreign agent's Agent Advertisement message,
this field is present and contains the key advertised in that
message, if the mobile node chooses to use the key.
The mobility security association assumed to exist between the home
agent and the mobile node will be used to encrypt the key unless a
Key Identification extension is also included with the Registration
Request message. The key returned by the home agent will be assumed,
by default, to be 128 bits long.
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4.4. Mobile Node Registration Key Extension
The Mobile Node Registration Key extension may be used on
Registration Reply messages to send a registration key from the
mobile node's home agent to the mobile node. When used, the home
agent must also include a Foreign Agent Registration Key extension in
the Registration Reply message, giving a copy of the same key to the
mobile node's new foreign agent. The Mobile Node Registration Key
extension is authenticated along with the rest of the Registration
Reply message, and thus no additional authenticator is included in
the extension.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Mobile Node Encrypted Key ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
99
Length
The length of the Mobile Node Encrypted Key
Mobile Node Encrypted Key
(variable length) The registration key, chosen by the home
agent, encrypted based on the mobility security association
between the home agent and the mobile node. The same key must
be sent, encrypted for the foreign agent in a Foreign Agent
Registration Key extension in this Registration Reply message.
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4.5. Foreign Agent Registration Key Extension
The Foreign Agent Registration Key extension may be used on
Registration Reply messages to send a registration key from
the mobile node's home agent to the mobile node's new foreign
agent. When used, the home agent must also include a Mobile Node
Registration Key extension in the Registration Reply message,
giving a copy of the same key to the mobile node. The Foreign
Agent Registration Key extension is authenticated by including an
authenticator in the extension, computed based on the mobility
security association shared between the home agent and the foreign
agent.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Foreign Agent Encrypted Key ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authenticator ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
100
Length
The length of the Foreign Agent Encrypted Key plus the length
of the Authenticator
Foreign Agent Encrypted Key
(variable length) The registration key, chosen by the home
agent, encrypted based on the mobility security association
between the home agent and the foreign agent, if one exists, or
based on the foreign agent public key from the Registration Key
Request message. The same key must be sent, encrypted for the
mobile node in a Mobile Node Registration Key extension in this
Registration Reply message.
Authenticator
(variable length) A hash value taken over a stream of bytes
including the shared secret and the fields in this extension
other than the Authenticator field itself.
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4.6. Foreign Agent Public Key Extension
The Foreign Agent Public Key Extension MAY be included by a foreign
agent in the Agent Advertisement messages that it sends. The
extension advertises the foreign agent's public encryption key, to
allow mobile nodes to include the key in a Registration Key Request
extension to their Registration Request message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Foreign Agent Public Key ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
101
Length
The length of the Foreign Agent Public Key
Foreign Agent Public Key
The foreign agent's public encryption key
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5. Mobility Security Association Management
5.1. Motivation
One of the most difficult aspects of Route Optimization for Mobile IP
in the Internet today is that of providing authentication for all
messages that affect the routing of datagrams to a mobile node.
In the basic Mobile IP protocol, all routing of datagrams to the
mobile node while away from its home network is controlled by the
home agent, since only the home agent is aware of the mobile node's
mobility binding and only the home agent tunnels datagrams to
the mobile node. Authentication is achieved based on a manually
established "mobility security association" between the home agent
and the mobile node. Since the home agent and the mobile node are
both owned by the same organization (both are assigned IP addresses
within the same IP subnet), this manual configuration is manageable,
and (for example) can be performed while the mobile node is at home.
With Route Optimization, though, there is a need in general to
authenticate messages between two nodes belonging to different
organizations, making establishment of a mobility security
association more difficult. Since no general authentication or key
distribution protocol is available in the Internet today, the Route
Optimization procedures defined in this document rely partially on
the same type of manually configured mobility security associations
used in the basic Mobile IP protocol.
For a correspondent node to be able to create a location cache entry
for a mobile node so that it can tunnel its own IP datagrams directly
to the mobile node at its current location, the correspondent node
and the mobile node's home agent must have established a mobility
security association. This mobility security association, though,
may be used in creating and updating location cache entries at
this correspondent node for all mobile nodes served by this home
agent. This places the correspondent node in a fairly natural
relationship with respect to the mobile nodes served by this home
agent. For example, these mobile nodes may represent different
people affiliated with the organization owning the home agent and
these mobile nodes, with which the user of this correspondent node
often collaborates. In this case, the effort of establishing the
necessary mobility security association with this home agent may be
justified. It is similarly possible for a mobile node to have a
manually established mobility security association with the foreign
agents that it commonly uses; when it does, there is no need to
obtain a registration key from the home agent.
However, the possibility of obtaining a registration key, as outlined
in Section 8.1, allows smooth handoffs to occur even in the absence
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of mutually assured identification between the mobile node and the
foreign agent. This feature depends for its operation on the fact
that the foreign agent has already agreed to provide service for the
mobile node; no additional verification of identity is required. In
other words, for the purposes of mobility protocols, if an agent acts
like a foreign agent, then it is a foreign agent.
In general, if the movement and communication patterns of a mobile
node or the group of mobile nodes served by the same home agent are
sufficient to justify establishing a mobility security association
with the mobile node's home agent, users or network administrators
are likely to do so. Establishing a mobility security association
is not a requirement to using the protocol. In that case, however,
the ability of correspondent nodes to use the Mobile IP protocol with
Route Optimization is severely restricted; datagrams destined for a
mobile node have to be routed through the mobile node's home agent,
to be tunneled to the mobile node's current location.
5.2. Mobility Security Associations
For use with Route Optimization, a mobility security association held
by a correspondent node or a foreign agent must in general include
the same parameters as required by the base Mobile IP protocol
specification [3].
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6. Location Cache Considerations
Any node may maintain a location cache in order to optimize its
own communication with mobile nodes. When sending a datagram, if
the node has a location cache entry for the destination node, it
may tunnel the datagram to the mobile node's care-of address using
the encapsulation techniques described for home agents in the base
Mobile IP protocol specification [3].
When a node other than the foreign agent currently serving a mobile
node receives a datagram for a mobile node, and this datagram has
been tunneled to that node, the node tunneling the datagram generally
has an out-of-date binding for the mobile node in its location
cache. In such cases, the node receiving the tunneled datagram may
send a Binding Warning message to the tunneling node, which should
then request a new binding for the mobile node by sending a Binding
Request message to the mobile node's home agent. Similarly, when a
mobile node's home agent intercepts a datagram on the home network
and tunnels it to the mobile node, the originating node typically
has no location cache entry for the destination mobile node. In
such cases, the home agent may send a Binding Update message to the
originator.
6.1. Cache Management
A node maintaining a location cache may use any reasonable strategy
for managing the space within the cache. When a new entry needs to
be added to the location cache, the node may choose to drop any entry
already in the cache, if needed, to make space for the new entry.
For example, a "least-recently used" (LRU) strategy for cache entry
replacement is likely to work well.
Each binding in the location cache also has an associated lifetime,
specified by in the Binding Update message in which the node obtained
the binding. After the expiration of this time period, the binding
MUST be dropped from the cache.
6.2. Receiving Binding Warning Messages
A node maintaining and using a location cache will receive a Binding
Warning message if its location cache entry for a datagram it has
tunneled is out-of-date, as determined by the node which receives the
tunneled datagram. The node receiving the Binding Warning message
then constructs a Binding Request message to obtain a new binding
from the home agent serving the mobile node. Included in the Binding
Request message is a 64-bit identification field, in the same format
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described in the base Mobile IP protocol document, for matching the
request with the returned Binding Update message. The node should
silently discard any Binding Update messages that do not correspond
with its latest Binding Request message for this mobile node.
6.3. Receiving Binding Update Messages
When a node receives a Binding Update message, it uses the
authentication technique indicated by the mobility security
association between itself and the mobile node's home agent. The
authentication data is found in the Route Optimization Authentication
Extension (Section 4.2). If the authentication succeeds, then a
location cache entry may be updated for use in future transmissions
of data to the mobile node. Otherwise, an authentication exception
SHOULD be raised.
6.4. Using Special Tunnels
Whenever any node receives a tunneled datagram for a mobile node,
for which no location cache entry or visitor list entry is known,
the node may determine that it has received the tunneled datagram
in error. In this case, the node should use a "special tunnel" to
make sure the datagram arrives at the home agent for the mobile node.
The home agent will then notify the originator of the tunnel about
its out-of-date location cache entry, and take steps to deliver the
datagram to the current care-of address of the mobile node. As part
of this service, the home agent must also check to make sure that the
datagram is not tunneled again to the node originating the special
tunnel.
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7. Home Agent Considerations
The home agent will be the frequent source of and Binding Update
messages sent to correspondent nodes which are communicating with its
mobile nodes. Any correspondent node which has no cached bindings
for a mobile node, will send normal, untunneled datagrams through
the home agent by the normal routing in the Internet. When the home
agent first gets a datagram for a mobile node, it SHOULD also send
a Binding Update message to the originator of the datagram in hopes
that the originator will be able to create a location cache entry for
that mobile node. Then, future transmissions for the mobile node
will not necessarily involve the home agent.
As time goes on, more and more Internet nodes will be able to
maintain location caches, and it is hoped that home agents will need
to be involved only rarely with routing datagrams to mobile nodes.
This might usually happen only when correspondent nodes first try to
initiate a session from a mobile node which has not been in contact
with the correspondent node for a long period of time.
7.1. Rate Limiting
A home agent must provide some mechanism to limit the rate at which
it sends Binding Update messages to to the same node about any given
mobility binding, after tunneling a datagram intercepted on the home
network. This is especially true because it is expected that most
Internet nodes will not be equipped with location caches for a long
time, and continual transmissions of Binding Warning messages to such
nodes will only exacerbate the problem of the traffic bottleneck at
the home agent.
7.2. Receiving Binding Request Messages
When the home agent receives a Binding Request message, it consults
its home list and determines the correct binding information to be
sent to the requesting node. Before satisfying the request, the
home agent must check whether or not the mobile node has allowed the
information to be disseminated. If the mobile node specified the 'P'
bit in its Registration Request, then the home agent must not satisfy
any binding Requests. Nevertheless, the home agent can return an
empty Binding Update, with a zero care-of address and zero lifetime,
so that the correspondent node will not go to the trouble of trying
to obtain a binding. This situation can never arise by the action of
any correctly operating node maintaining a location cache, but it is
still possible that an intelligent correspondent node might try to
obtain bindings for mobile nodes.
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7.3. Receiving Registration Key requests
When the home agent receives a Registration Request message, it may
also be asked to compute registration keys for use with foreign
agent handoffs (Section 2.2). In that event, the home agent employs
a good algorithm for producing random keys [2] and encrypts the
result separately for use by the foreign agent and by the mobile
node. The chosen key is encrypted under a key and algorithm shared
between the home agent and the mobile node, and the encrypted key
is placed in a Mobile Node Registration Key extension (Section 4.4)
in the Registration Reply message. The same key also is encrypted
under a key and algorithm shared between the home agent and the
foreign agent, and the encrypted key is placed in a Foreign Agent
Registration Key extension (Section 4.5) in the Registration Reply
message. By default, the home agent uses its mobility security
association for the mobile node and for the foreign agent to encrypt
the registration key. If the home agent has no preestablished
mobility security association with the foreign agent and the
Registration Key Request extension contained a public key from the
foreign agent, the home agent may instead use this key to encrypt the
registration key for the foreign agent.
7.4. Receiving Special Tunnels
The home agent can also receive tunneled datagrams destined for the
mobile node. If the tunnel source is the same as the foreign agent
shown in the home list entry for the mobile node, then the home
agent MUST NOT send the datagram back to that same foreign agent.
Otherwise, the home agent can tunnel the tunneled datagram to the
current foreign agent, encapsulating the incoming tunneled datagram
in its entirety.
The home agent also, in this case, takes responsibility for sending
information to the originator of the datagram (whose source address
will be in the inner datagram header inside the encapsulation),
to allow that originator to update its location cache entry for
the target mobile node. If the home agent has a mobility security
association with the correspondent node which originated the
datagram, an authenticated Binding Update message can be sent
directly.
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8. Foreign Agent Considerations
In addition to managing the resources needed to handle basic
Mobile IP registrations, the foreign agent assisting with Route
Optimization assumes two additional responsibilities. The first
is the maintenance of a location cache for forwarding datagrams to
mobile nodes as they switch connections to new foreign agents. The
second is a slight modification of the registration procedure, to
allow for timely notification possible for previous foreign agents.
8.1. Setting up Temporary Mobility Security Associations
As part of the registration procedure, a mobile node and foreign
agent can agree on a registration key. This registration key is, as
described in Section 7.3, computed by the mobile node's home agent
and transmitted back to the foreign agent along with the Registration
Reply message. Within this document, the registration key is used
only for authentication of a single Binding Update message; other
uses for the registration key are possible, but are outside the scope
of this discussion. For instance, the foreign agent and mobile node
may negotiate to use the registration key to provide confidentiality
along the wireless link connecting them. If a foreign agent is
unable to process a registration request because the mobile node also
expects a registration key, the foreign agent returns the appropriate
status code immediately in a Registration Reply message.
DISCUSSION: Alternatively, we could add a bit to the Agent
Advertisement message.
The actual request for the registration key is made by the mobile
node (Section 2.2). Since the foreign agent and the home agent
may have no mobility security association, the home agent cannot
be assured of the identity of the foreign agent. This does not
matter, however, for the production of the registration key. When
the foreign agent receives the registration reply, with both foreign
agent registration key extensions, it strips off the extension
containing its own registration key, and relays the rest to the
mobile node.
This registration key can be trusted for the purposes outlined, even
though the mobile node and the foreign agent cannot be expected to
always authenticate each other's identity. They can, however, expect
each other to follow the operational procedures comprising the Route
Optimization protocols. Any further use made of the registration key
must take into account the fact that the nodes involved have not yet
mutually identified each other in a trustworthy fashion; they have
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only agreed that the foreign agent will provide certain desirable
services to the mobile node.
8.2. Previous Foreign Agent Notification
When a mobile node registers with a new foreign agent, it may request
that the new foreign agent send a Binding Update message to its
previous foreign agent. This Binding Update must be authenticated,
using the Route Optimization Authentication extension (Section 4.2),
as must all Binding Updates. The Acknowledge bit in this Binding
Update message must be set.
When the previous foreign agent receives the Binding Update, it will
use the mobility security association set up with the mobile node
during its previous registration to authenticate the message. If
the message authentication is correct, the old visitor list entry
will be deleted and a Binding Acknowledge message returned to the
sender. In addition, if a new care-of address was included with the
new binding, a location cache entry will be created for it, and the
previous foreign agent can tunnel datagrams to the mobile node's
current care-of address using that location cache, just as any node
maintaining a location cache.
In particular, the previous foreign agent can tunnel the Binding
Acknowledge message back to the new care-of address specified in
the received binding. This creates an interesting problem for the
new foreign agent when it receives the acknowledgment before the
registration reply from the home agent. It is suggested that the new
foreign agent deliver the acknowledgment to the mobile node anyway,
even though the mobile node is technically unregistered. If there
is concern that this provides a loophole for unauthorized traffic
to the mobile node, the new foreign agent could limit the number of
datagrams delivered to the unregistered mobile node to this single
instance. Alternatively, a new extension to the Registration Reply
message can be defined to carry along the acknowledgement from the
previous foreign agent. This latter approach would have the benefit
that fewer datagrams would be transmitted over bandwidth-constrained
wireless media during registrations.
The lifetime associated with the location cache, in this situation,
can be substantially shorter than other location caches for several
reasons. First, the home agent is presumably tunneling datagrams to
the new foreign agent; second, any active correspondent node will
probably get a new location cache entry for the mobile node after
receiving the Binding Warning message from the previous foreign
agent. Lastly, even if the location cache entry expires prematurely,
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the previous foreign agent can special tunnel any straggling
datagrams back to the home agent for further delivery.
8.3. Receiving Tunneled Datagrams
If the mobile node's current foreign agent receives a tunneled
datagram for the mobile node, it can be assumed that the tunneled
datagram was originated by a node maintaining a location cache.
There may be pathological or special cases where this assumption is
false, but one would almost have to intentionally run custom code
to invalidate the assumption. Since the foreign agent currently
serving a mobile node can assume that the sending node forwarded the
datagram based on correct location cache information, the foreign
agent can also assume that the sending cache agent has already issued
notification to the source of the original datagram. Thus, the
current foreign agent never needs to send a Binding Warning message
to the node which last tunneled the datagram.
On the other hand, a foreign agent which is tunneling received
datagrams on behalf of a mobile node not in its visitor list should,
just as any other node implementing Route Optimization, send Binding
Warning messages to the originator of these datagrams. If the
datagrams it receives are not tunneled, the foreign agent should
limit the rate at which it sends Binding Warning messages to the
originators, since those originators may be unable to interpret such
notifications. It is expected that reception of such un-tunneled
datagrams by any foreign agent will be rare.
8.4. Sending Special Tunnels
If a foreign agent receives a tunneled datagram for a mobile node
which is unknown, then the foreign agent can tunnel the datagram back
to the home agent. This requires special care at the home agent.
The foreign agent must use the mobile node's address as the tunnel
destination, and its own address as the tunnel source. The home
agent will then capture the special tunneled datagram and re-tunnel
it to the mobile node via its current foreign agent. The foreign
agent sending the special tunnel should not notify the originator of
the datagram about its out-of-date binding, as this will be done by
the home agent which receives the special tunnel datagram.
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9. Mobile Node Considerations
9.1. Requesting a Registration Key
When a mobile node makes a registration request, it can request a
registration key to be shared between itself and the prospective
foreign agent. The key will be used to authenticate a future
disconnection notice from the mobile node, when the mobile node
has moved to a new cell. The mobile node allows the home agent to
pick the registration key, because it is expected that the mobile
node is less likely to have good means for computing pseudo-random
numbers [2]. The registration key will be returned in an extension
to the expected registration reply, and the foreign agent can use
it to compute a "mobile-foreign" authentication extension to the
registration reply. If this is done, the mobile node will have
complete confidence that it does in fact share a secret registration
key. If not, the mobile node can still act on the supposition that
the key has been correctly received by the foreign agent, but the
delivery of the key to the foreign agent can be compromised by an
active attack which modifies some of the bits of the extension which
the home agent uses to deliver the key to the foreign agent. In the
latter case, the foreign agent does not have a good way to detect the
corruption. Since the problem will only show up by possibly causing
some datagrams to be lost after some unpredictably distant future
movement by the mobile node, it is not absolutely required to test
the validity of the registration key.
If the mobile node detects that the foreign agent has a corrupted
registration key, it can re-register immediately.
9.2. Notifying Previous Foreign Agents
If the mobile node wishes to instruct its prospective foreign agent
to send a Binding Update message to the mobile node's previous
foreign agent, it uses the appropriate extension (see 4.1) to the
Registration Request message. This usually results in quicker
establishment of a location cache entry at the previous foreign
agent, because the previous foreign agent is likely to be much closer
to the new foreign agent than the home agent is.
Since the prospective new foreign agent does not have access to
the registration key which was established between the mobile node
and its previous foreign agent, the mobile node has to compute
the appropriate authentication value for use by the prospective
foreign agent. This authentication is computed over the fields of
the expected Binding Update message, with the 'I' bit set and no
identification present. Reply protection is considered unnecessary
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since the binding update is expected to be sent only once with the
registration key.
When the acknowledgment arrives, the new foreign agent detunnels
it and sends it to the mobile node. In this way, the mobile node
can still discover that its previous foreign agent has updated
its visitor list and location cache. This is important, because
otherwise the previous foreign agent would often become a "black
hole" for datagrams destined for the mobile node. The new foreign
agent has no further responsibility for helping to update the
location cache at the previous foreign agent.
The mobile node expects to eventually receive an acknowledgement
from its previous foreign agent, signifying that the mobile node's
entry has been erased from its visitor list. If the acknowledgement
has not been received after sufficient time, the mobile node is
responsible for retransmitting another Binding Update message to
its previous foreign agent. Although the previous foreign agent
may have already deleted the registration key from its records, the
mobile node should continue to retransmit its Binding Update message
until the previous foreign agent responds with either a positive or
negative acknowledgment.
Since the mobile node is responsible for fielding the acknowledgement
from its previous foreign agent, there is no need to add any status
code or bit to the Registration Reply from its prospective new
foreign agent
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References
[1] Ralph Droms. Dynamic Host Configuration Protocol. RFC 1541,
October 1993.
[2] Donald E. Eastlake 3rd, Stephen D. Crocker, and Jeffrey I.
Schiller. Randomness recommendations for security. RFC 1750,
December 1994.
[3] Charles Perkins, editor. IP mobility support. Internet Draft,
draft-ietf-mobileip-protocol-08.txt, January 1995. Work in
progress.
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Appendix A. Using a Master Key at the Home Agent
Rather than storing each mobility security association that it has
established with many different correspondent nodes and foreign
agents, a home agent may manage its mobility security associations so
that each of them can be generated from a single "master" key. With
the master key, the home agent could build a key for any given other
node by computing the node-specific key as
MD5(node-address || master-key || node-address)
where node-address is the IP address of the particular node for which
the home agent is building a key, and master-key is the single master
key held by the home agent for all mobility security associations it
has established with correspondent nodes. The node-specific key is
built by computing an MD5 hash over a string consisting of the master
key with the node-address concatenated as a prefix and as a suffix.
Using this scheme, when establishing each mobility security
association, the network administrator managing the home agent
computes the node-specific key and communicates this key to the
network administrator of the other node through some "secure"
channel, such as over the telephone. The mobility security
association is configured at this other node in the same way as any
mobility security association. At the home agent, though, no record
need be kept that this key has been given out. The home agent need
only be configured to know that this scheme is in use for all of its
mobility security associations.
When the home agent then needs a mobility security association as
part of the Route Optimization protocol, it builds the node-specific
key based on the master key and the IP address of the other node with
which it is attempting to authenticate. If the other node knows
the correct node-specific key, the authentication will succeed;
otherwise, it will fail as it should.
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Chairs' Addresses
The working group can be contacted via the current chairs:
Tony Li
cisco Systems
170 W. Tasman Dr.
San Jose CA 95134
Phone: +1-408-526-8186
E-mail: tli@cisco.com
Jim Solomon
Motorola, Inc.
Phone: +1-708-576-2753
E-mail: solomon@comm.mot.com
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Authors' Addresses
Questions about this document can also be directed to the authors:
David B. Johnson
Computer Science Department
Carnegie Mellon University
5000 Forbes Avenue
Pittsburgh, PA 15213-3891
Phone: +1-412-268-7399
Fax: +1-412-268-5576
E-mail: dbj@cs.cmu.edu
Charles Perkins
Room J1-A25
T. J. Watson Research Center
IBM Corporation
30 Saw Mill River Rd.
Hawthorne, NY 10532
Phone: +1-914-784-7350
Fax: +1-914-784-7007
E-mail: perk@watson.ibm.com
Andrew Myles
Electronics Department
Macquarie University 2109
Sydney, Australia
Phone: +61-2-8059071
Fax: +61-2-8059128
E-mail: andrewm@mpce.mq.edu.au
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