NETLMM WG S. Gundavelli
Internet-Draft K. Leung
Intended status: Standards Track Cisco
Expires: March 14, 2008 V. Devarapalli
Azaire Networks
K. Chowdhury
Starent Networks
B. Patil
Nokia Siemens Networks
September 11, 2007
Proxy Mobile IPv6
draft-ietf-netlmm-proxymip6-04.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This specification describes a network-based mobility management
protocol. It is called Proxy Mobile IPv6 and is based on Mobile IPv6
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[RFC-3775]. This protocol enables mobility support to a host without
requiring its participation in any mobility related signaling. The
design principle in the case of network-based mobility management
protocol relies on the network being in control of the mobility
management. The mobility entities in the network are responsible for
tracking the movements of the host and initiating the required
mobility signaling on its behalf.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions & Terminology . . . . . . . . . . . . . . . . . . 5
2.1. Conventions used in this document . . . . . . . . . . . . 5
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
3. Proxy Mobile IPv6 Protocol Overview . . . . . . . . . . . . . 8
4. Proxy Mobile IPv6 Protocol Security . . . . . . . . . . . . . 13
4.1. Peer Authorization Database Entries . . . . . . . . . . . 13
4.2. Security Policy Database Entries . . . . . . . . . . . . . 14
5. Local Mobility Anchor Operation . . . . . . . . . . . . . . . 15
5.1. Extensions to Binding Cache Entry Data Structure . . . . . 15
5.2. Supported Home Network Prefix Models . . . . . . . . . . . 16
5.3. Signaling Considerations . . . . . . . . . . . . . . . . . 16
5.4. Timestamp Option for Message Ordering . . . . . . . . . . 21
5.5. Routing Considerations . . . . . . . . . . . . . . . . . . 23
5.5.1. Bi-Directional Tunnel Management . . . . . . . . . . . 23
5.5.2. Forwarding Considerations . . . . . . . . . . . . . . 23
5.6. Local Mobility Anchor Address Discovery . . . . . . . . . 24
5.7. Mobile Prefix Discovery Considerations . . . . . . . . . . 25
5.8. Route Optimizations Considerations . . . . . . . . . . . . 25
6. Mobile Access Gateway Operation . . . . . . . . . . . . . . . 25
6.1. Extensions to Binding Update List Entry Data Structure . . 26
6.2. Mobile Node's Policy Profile . . . . . . . . . . . . . . . 27
6.3. Supported Access Link Types . . . . . . . . . . . . . . . 28
6.4. Supported Address Configuration Models . . . . . . . . . . 28
6.5. Access Authentication & Mobile Node Identification . . . . 28
6.6. Acquiring Mobile Node's Identifier . . . . . . . . . . . . 29
6.7. Home Network Emulation . . . . . . . . . . . . . . . . . . 29
6.8. Link-Local and Global Address Uniqueness . . . . . . . . . 30
6.9. Signaling Considerations . . . . . . . . . . . . . . . . . 31
6.9.1. Binding Registrations . . . . . . . . . . . . . . . . 31
6.9.2. Router Solicitation Messages . . . . . . . . . . . . . 34
6.9.3. Retransmissions and Rate Limiting . . . . . . . . . . 35
6.10. Routing Considerations . . . . . . . . . . . . . . . . . . 35
6.10.1. Transport Network . . . . . . . . . . . . . . . . . . 36
6.10.2. Tunneling & Encapsulation Modes . . . . . . . . . . . 36
6.10.3. Routing State . . . . . . . . . . . . . . . . . . . . 37
6.10.4. Local Routing . . . . . . . . . . . . . . . . . . . . 38
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6.10.5. Tunnel Management . . . . . . . . . . . . . . . . . . 38
6.10.6. Forwarding Rules . . . . . . . . . . . . . . . . . . . 38
6.11. Interaction with DHCP Relay Agent . . . . . . . . . . . . 40
6.12. Home Network Prefix Renumbering . . . . . . . . . . . . . 40
6.13. Mobile Node Detachment Detection and Resource Cleanup . . 40
6.14. Allowing network access to other IPv6 nodes . . . . . . . 41
7. Mobile Node Operation . . . . . . . . . . . . . . . . . . . . 42
7.1. Moving into a Proxy Mobile IPv6 Domain . . . . . . . . . . 42
7.2. Roaming in the Proxy Mobile IPv6 Domain . . . . . . . . . 43
7.3. IPv6 Host Protocol Parameters . . . . . . . . . . . . . . 43
8. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 44
8.1. Proxy Binding Update Message . . . . . . . . . . . . . . . 45
8.2. Proxy Binding Acknowledgement Message . . . . . . . . . . 46
8.3. Home Network Prefix Option . . . . . . . . . . . . . . . . 46
8.4. Link-local Address Option . . . . . . . . . . . . . . . . 47
8.5. Timestamp Option . . . . . . . . . . . . . . . . . . . . . 48
8.6. Status Values . . . . . . . . . . . . . . . . . . . . . . 49
9. Protocol Configuration Variables . . . . . . . . . . . . . . . 50
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51
11. Security Considerations . . . . . . . . . . . . . . . . . . . 51
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 52
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 53
13.1. Normative References . . . . . . . . . . . . . . . . . . . 53
13.2. Informative References . . . . . . . . . . . . . . . . . . 54
Appendix A. Proxy Mobile IPv6 interactions with AAA
Infrastructure . . . . . . . . . . . . . . . . . . . 55
Appendix B. Supporting Shared-Prefix Model using DHCPv6 . . . . . 55
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 56
Intellectual Property and Copyright Statements . . . . . . . . . . 57
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1. Introduction
Mobile IPv6 [RFC-3775] is the enabler for IPv6 mobility. It requires
Mobile IPv6 client functionality in the IPv6 stack of a mobile node.
Signaling between the mobile node and home agent enables the creation
and maintenance of a binding between the mobile node's home address
and care-of-address. Mobile IPv6 has been designed to be an integral
part of the IPv6 stack in a host. However there exist IPv6 stacks
today that do not have Mobile IPv6 functionality and there would
likely be IPv6 stacks without Mobile IPv6 client functionality in the
future as well. It is desirable to support IP mobility for all hosts
irrespective of the presence or absence of mobile IPv6 functionality
in the IPv6 stack.
It is possible to support mobility for IPv6 nodes by extending Mobile
IPv6 [RFC-3775] signaling and reusing the home agent via a proxy
mobility agent in the network. This approach to supporting mobility
does not require the mobile node to be involved in the signaling
required for mobility management. The proxy mobility agent in the
network performs the signaling and does the mobility management on
behalf of the mobile node. Because of the use and extension of
Mobile IPv6 signaling and home agent functionality, this protocol is
referred to as Proxy Mobile IPv6 (PMIPv6).
Network deployments which are designed to support mobility would be
agnostic to the capability in the IPv6 stack of the nodes which it
serves. IP mobility for nodes which have mobile IP client
functionality in the IPv6 stack as well as those hosts which do not,
would be supported by enabling Proxy Mobile IPv6 protocol
functionality in the network. The advantages of developing a network
based mobility protocol based on Mobile IPv6 are:
o Reuse of home agent functionality and the messages/format used in
mobility signaling. Mobile IPv6 is a mature protocol with several
implementations that have been through interoperability testing.
o A common home agent would serve as the mobility agent for all
types of IPv6 nodes.
o Addresses a real deployment need.
The problem statement and the need for a network based mobility
protocol solution has been documented in [RFC-4830]. Proxy Mobile
IPv6 is a solution that addresses these issues and requirements.
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2. Conventions & Terminology
2.1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC-2119].
2.2. Terminology
All the general mobility related terms used in this document are to
be interpreted as defined in the Mobile IPv6 base specification [RFC-
3775].
This document adopts the terms, Local Mobility Anchor (LMA) and
Mobile Access Gateway (MAG) from the NETLMM Goals document [RFC-
4831]. This document also provides the following context specific
explanation to the following terms used in this document.
Proxy Mobile IPv6 Domain (PMIPv6-Domain)
Proxy Mobile IPv6 domain refers to the network where the mobility
management of a mobile node is handled using Proxy Mobile IPv6
protocol as defined in this specification. The Proxy Mobile IPv6
domain includes local mobility anchors and mobile access gateways
between which security associations can be setup and authorization
for sending Proxy Binding Updates on behalf of the mobile nodes
can be ensured.
Local Mobility Anchor (LMA)
Local Mobility Anchor is the home agent for the mobile node in the
Proxy Mobile IPv6 domain. It is the topological anchor point for
the mobile node's home network prefix and is the entity that
manages the mobile node's reachability state. It is important to
understand that the local mobility anchor has the functional
capabilities of a home agent as defined in Mobile IPv6 base
specification [RFC-3775] and with the additional required
capabilities for supporting Proxy Mobile IPv6 protocol as defined
in this specification.
Mobile Access Gateway (MAG)
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Mobile Access Gateway is a function that manages the mobility
related signaling for a mobile node that is attached to its access
link. It is responsible for tracking the mobile node's movements
on the access link and for signaling the mobile node's local
mobility anchor.
Mobile Node (MN)
Through out this document, the term mobile node is used to refer
to an IP host whose mobility is managed by the network. The
mobile node may be operating in IPv6 mode, IPv4 mode or in IPv4/
IPv6 dual mode. The mobile node is not required to participate in
any mobility related signaling for achieving mobility for an IP
address that is obtained in that Proxy Mobile IPv6 domain. This
document further uses explicit text when referring to a mobile
node that is involved in mobility related signaling as per Mobile
IPv6 specification [RFC-3775].
LMA Address (LMAA)
The address that is configured on the interface of the local
mobility anchor and is the transport endpoint of the bi-
directional tunnel established between the local mobility anchor
and the mobile access gateway. This is the address to where the
mobile access gateway sends the Proxy Binding Update messages.
When supporting IPv4 traversal, i.e., when the network between the
local mobility anchor and the mobile access gateway is an IPv4
network, this address will be an IPv4 address and will be referred
to as IPv4-LMAA, as specified in [ID-IPV4-PMIP6].
Proxy Care-of Address (Proxy-CoA)
Proxy-CoA is the address configured on the interface of the mobile
access gateway and is the transport endpoint of the tunnel between
the local mobility anchor and the mobile access gateway. The
local mobility anchor views this address as the Care-of Address of
the mobile node and registers it in the Binding Cache entry for
that mobile node. When the transport network between the mobile
access gateway and the local mobility anchor is an IPv4 network
and if the care-of address that is registered at the local
mobility anchor is an IPv4 address, the term, IPv4-Proxy-CoA is
used, as specified in [ID-IPV4-PMIP6].
Mobile Node's Home Address (MN-HoA)
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MN-HoA is the home address of a mobile node in a Proxy Mobile IPv6
domain. It is an address from its home network prefix obtained by
a mobile node in a Proxy Mobile IPv6 domain. The mobile node can
continue to use this address as long as it is attached to the
network that is in the scope of that Proxy Mobile IPv6 domain.
Mobile Node's Home Network Prefix (MN-HNP)
This is the on-link IPv6 prefix that is always present in the
Router Advertisements that the mobile node receives when it is
attached to any of the access links in that Proxy Mobile IPv6
domain. This home network prefix is topologically anchored at the
mobile node's local mobility anchor. The mobile node configures
its interface with an address from this prefix.
Mobile Node's Home Link
This is the link on which the mobile node obtained its initial
address configuration after it moved into that Proxy Mobile IPv6
domain. This is the link that conceptually follows the mobile
node. The network will ensure the mobile node always sees this
link with respect to the layer-3 network configuration, on any
access link that it attaches to in that Proxy Mobile IPv6 domain.
Mobile Node Identifier (MN-Identifier)
The identity of a mobile node in the Proxy Mobile IPv6 domain.
This is the stable identifier of a mobile node that the mobility
entities in a Proxy Mobile IPv6 domain can always acquire and
using which a mobile node can predictably be identified. This is
typically an identifier such as Mobile Node NAI [RFC-4282].
Proxy Binding Update (PBU)
A binding registration request message sent by a mobile access
gateway to a mobile node's local mobility anchor for establishing
a binding between the mobile node's MN-HNP and the Proxy-CoA.
Proxy Binding Acknowledgement (PBA)
A binding registration reply message sent by a local mobility
anchor in response to a Proxy Binding Update request message that
it received from a mobile access gateway.
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3. Proxy Mobile IPv6 Protocol Overview
This specification describes a network-based mobility management
protocol. It is called Proxy Mobile IPv6 and is based on Mobile IPv6
[RFC-3775].
Proxy Mobile IPv6 protocol is intended for providing network-based
mobility management support to a mobile node, without requiring the
participation of the mobile node in any mobility related signaling.
The mobility entities in the network will track the mobile node's
movements and will initiate the mobility signaling and setup the
required routing state.
The core functional entities in the NETLMM infrastructure are the
Local Mobility Anchor and the Mobile Access Gateway. The local
mobility is responsible for maintaining the mobile node's
reachability state and is the topological anchor point for the mobile
node's home network prefix. While the mobile access gateway is the
entity that performs the mobility management on behalf of a mobile
node and it resides on the access link where the mobile node is
anchored. The mobile access gateway is responsible for detecting the
mobile node's movements on its access link and for sending binding
registrations to the mobile node's local mobility anchor.
+----+ +----+
|LMA1| |LMA2|
+----+ +----+
LMAA1 -> | | <-- LMAA2
| |
\\ //\\
\\ // \\
\\ // \\
+---\\------------- //------\\----+
( \\ IPv4/IPv6 // \\ )
( \\ Network // \\ )
+------\\--------//------------\\-+
\\ // \\
\\ // \\
\\ // \\
Proxy-CoA1--> | | <-- Proxy-CoA2
+----+ +----+
|MAG1|-----{MN2} |MAG2|
+----+ | +----+
| | |
MN-HoA1 --> | MN-HoA2 | <-- MN-HoA3
{MN1} {MN3}
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Figure 1: Proxy Mobile IPv6 Domain
Once a mobile node enters a Proxy Mobile IPv6 domain and attaches to
an access network, the mobile access gateway on that access network
after identifying the mobile node and acquiring its identifier, will
determine if the mobile node is authorized for network-based mobility
management service.
If the network determines that the network-based mobility management
service needs to be offered to that mobile node, the network will
ensure that the mobile node using any of the address configuration
mechanisms permitted by the network, will be able to obtain an
address from its home network prefix and move anywhere in that proxy
mobile IPv6 domain. From the perspective of the mobile node, the
entire proxy mobile IPv6 domain appears as a single link, the network
ensures that the mobile node believes it is always on the same link
where it obtained its initial address configuration, even after
changing its point of attachment in that network.
The mobile node may be operating in an IPv4-only mode, IPv6-only mode
or in dual IPv4/IPv6 mode. Based on what is enabled in the network
for that mobile node, the mobile node will be able to obtain an IPv4,
IPv6 or dual IPv4/IPv6 addresses and move any where in that Proxy
Mobile IPv6 domain. However, the specific details related to the
IPv4 addressing or IPv4 transport support is specified in the
companion document [ID-IPV4-PMIP6].
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+-----+ +-----+ +-----+
| MN | | MAG | | LMA |
+-----+ +-----+ +-----+
| | |
MN Attached | |
| | |
| MN Attached Event |
| (Acquire MN-Id and Profile) |
| | |
| |----- PBU ----------->|
| | |
| | Accept PBU
| | (Allocate MN-HNP, Setup BCE and Tunnel)
| | |
| |<--------- PBA -------|
| | |
| Accept PBA |
| (Setup Tunnel and Routing) |
| | |
| |==== Bi-Dir Tunnel ===|
| | |
|--- Rtr Sol --------->| |
| | |
|<------- Rtr Adv -----| |
| | |
IP Address | |
Configuration | |
| | |
Figure 2: Mobile Node Attachment - Signaling Call Flow
Figure 2 shows the signaling call flow, when the mobile node enters
the Proxy Mobile IPv6 domain.
For updating the local mobility anchor about the current location of
the mobile node, the mobile access gateway sends a Proxy Binding
Update message to the mobile node's local mobility anchor. Upon
accepting this Proxy Binding Update message, the local mobility
anchor sends a Proxy Binding Acknowledgement message including the
mobile node's home network prefix. It also creates the Binding Cache
entry and establishes a bi-directional tunnel to the mobile access
gateway.
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The mobile access gateway on receiving the Proxy Binding
Acknowledgement message sets up a bi-directional tunnel to the local
mobility anchor and sets up the data path for the mobile node's
traffic. At this point the mobile access gateway will have all the
required information for emulating the mobile node's home link. It
sends Router Advertisement messages to the mobile node on the access
link advertising the mobile node's home network prefix as the hosted
on-link-prefix.
The mobile node on receiving these Router Advertisement messages on
the access link will attempt to configure its interface either using
stateful or stateless address configuration modes, based on the modes
that are permitted on that access link. At the end of a successful
address configuration procedure, the mobile node will end up with an
address from its home network prefix.
Once the address configuration is complete, the mobile node has a
valid address from its home network prefix, at the current point of
attachment. The serving mobile access gateway and the local mobility
anchor also have proper routing states for handling the traffic sent
to and from the mobile node using an address from its home network
prefix.
The local mobility anchor, being the topological anchor point for the
mobile node's home network prefix, receives any packets that are sent
by any corresponding node to the mobile node. Local mobility anchor
forwards these received packets to the mobile access gateway through
the bi-directional tunnel. The mobile access gateway on other end of
the tunnel, after receiving the packet, removes the outer header and
forwards the packet on the access link to the mobile node.
The mobile access gateway typically acts as a default router on the
access link. However, in some configurations where the functionality
of the mobile access gateway is split across different nodes, the
node sending the Router Advertisements will be the default-router for
the mobile node. Any packet that the mobile node sends to any
corresponding node will be received by the mobile access gateway and
will be sent to its local mobility anchor through the bi-directional
tunnel. The local mobility anchor on the other end of the tunnel,
after receiving the packet removes the outer header and routes the
packet to the destination.
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+-----+ +-----+ +-----+ +-----+
| MN | |p-MAG| | LMA | |n-MAG|
+-----+ +-----+ +-----+ +-----+
| | | |
| |==Bi-Dir Tunnel=| |
MN Detached | | |
| MN Detached Event | |
| | | |
| |-- PBU -------->| |
| | | |
| | Accept PBU |
| | (Start BCE delete timer) |
| | | |
| |<-------- PBA --| |
| | | |
MN Attached | | |
| | | MN Attached Event
| | | (Acquire MN-Id and Profile)
....
Registration steps as in fig 2.
....
| | |==Bi-Dir Tunnel=|
|--- Rtr Sol ------------------------------------->|
| | | |
|<------------------------------------ Rtr Adv ----|
| | | |
MN retains HoA/HNP
| | | |
Figure 3: Mobile Node Handoff - Signaling Call Flow
Figure 3 shows the signaling call flow for the mobile node's handoff
scenario.
After obtaining the initial address configuration in the Proxy Mobile
IPv6 domain, if the mobile node changes its point of attachment, the
mobile access gateway on the new access link, will signal the local
mobility anchor for updating the binding and routing state. The
mobile node will continue to receive the Router Advertisements
containing its home network prefix, making it believe its still on
the same link and can use the same address configuration on the new
access link.
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4. Proxy Mobile IPv6 Protocol Security
The signaling messages, Proxy Binding Update and Proxy Binding
Acknowledgement, exchanged between the mobile access gateway and the
local mobility anchor MUST be protected using end-to-end security
association(s) offering integrity and data origin authentication. A
security association with the mobile node for which the signaling
message is issued is not required for protection of these messages.
The mobile access gateway and the local mobility anchor MUST
implement IPsec for protecting the Proxy Mobile IPv6 signaling
messages [RFC-4301]. IPsec is the default security mechanism for
securing the signaling messages. However in certain deployments of
this protocol, other security mechanisms MAY be applied and the
signaling messages must be protected using the semantics provided by
that respective mechanism.
IPsec ESP [RFC-4303] in transport mode with mandatory integrity
protection SHOULD be used for protecting the signaling messages.
Confidentiality protection of these messages is not required.
IKEv2 [RFC-4306] SHOULD be used to setup security associations
between the mobile access gateway and the local mobility anchor to
protect the Proxy Binding Update and Proxy Binding Acknowledgement
messages. The mobile access gateway and the local mobility anchor
can use any of the authentication mechanisms, as specified in IKEv2,
for mutual authentication.
Mobile IPv6 specification [RFC-3775] requires the home agent to
prevent a mobile node from creating security associations or creating
binding cache entries for another mobile node's home address. In the
protocol described in this document, the mobile node is not involved
in creating security associations for protecting the signaling
messages or sending binding updates. Therefore, this is not a
concern. However, the local mobility anchor MUST allow only
authorized mobile access gateways to create binding cache entries on
behalf of the mobile nodes. The actual mechanism by which the local
mobility anchor verifies if a specific mobile access gateway is
authorized to send Proxy Binding Updates on behalf of a mobile node
is outside the scope of this document. One possible way this could
be achieved is by sending a query to the policy store, such as AAA.
4.1. Peer Authorization Database Entries
This section describes PAD entries on the mobile access gateway and
the local mobility anchor. The PAD entries are only example
configurations. Note that the PAD is a logical concept and a
particular mobile access gateway or a local mobility anchor
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implementation can implement the PAD in any implementation specific
manner. The PAD state may also be distributed across various
databases in a specific implementation.
mobile access gateway PAD:
- IF remote_identity = lma_identity_1
Then authenticate (shared secret/certificate/EAP)
and authorize CHILD_SA for remote address lma_addres_1
local mobility anchor PAD:
- IF remote_identity = mag_identity_1
Then authenticate (shared secret/certificate/EAP)
and authorize CHILD_SAs for remote address mag_address_1
The list of authentication mechanisms in the above examples is not
exhaustive. There could be other credentials used for authentication
stored in the PAD.
4.2. Security Policy Database Entries
This section describes the security policy entries on the mobile
access gateway and the local mobility anchor required to protect the
Proxy Mobile IPv6 signaling messages. The SPD entries are only
example configurations. A particular mobile access gateway or a
local mobility anchor implementation could configure different SPD
entries as long as they provide the required security.
In the examples shown below, the identity of the mobile access
gateway is assumed to be mag_1, the address of the mobile access
gateway is assumed to be mag_address_1, and the address of the local
mobility anchor is assumed to be lma_address_1.
mobile access gateway SPD-S:
- IF local_address = mag_address_1 &
remote_address = lma_address_1 &
proto = MH & local_mh_type = BU & remote_mh_type = BA
Then use SA ESP transport mode
Initiate using IDi = mag_1 to address lma_1
local mobility anchor SPD-S:
- IF local_address = lma_address_1 &
remote_address = mag_address_1 &
proto = MH & local_mh_type = BA & remote_mh_type = BU
Then use SA ESP transport mode
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5. Local Mobility Anchor Operation
For supporting the Proxy Mobile IPv6 protocol specified in this
document, the home agent function, specified in [RFC-3775] requires
certain functional modifications and enhancements. The home agent
with these modifications and enhanced capabilities for supporting
Proxy Mobile IPv6 protocol is referred to as the local mobility
anchor.
The section describes the operational details of the local mobility
anchor.
5.1. Extensions to Binding Cache Entry Data Structure
Every local mobility anchor MUST maintain a Binding Cache entry for
each currently registered mobile node. Binding Cache entry is a
conceptual data structure, described in Section 9.1 [RFC-3775].
For supporting this specification, the Binding Cache Entry data
structure needs to be extended with the following additional fields.
o A flag indicating whether or not this Binding Cache entry is
created due to a proxy registration. This flag is enabled for
Binding Cache entries that are proxy registrations and is turned
off for all other entries that are created due to the
registrations directly sent by the mobile node.
o The identifier of the registered mobile node, MN-Identifier. This
identifier is obtained from the NAI Option [RFC-4283] present in
the received Proxy Binding Update request.
o The Link-local address of the mobile node on the interface
attached to the access link. This is obtained from the Link-local
Address option, present in the Proxy Binding Update request.
o The IPv6 home network prefix of the registered mobile node. The
home network prefix of the mobile node may have been statically
configured in the mobile node's policy profile, or, it may have
been dynamically allocated by the local mobility anchor. The IPv6
home network prefix also includes the corresponding prefix length.
o The interface identifier of the bi-directional tunnel established
between the local mobility anchor and the mobile access gateway
where the mobile node is currently anchored. The tunnel interface
identifier is acquired during the tunnel creation.
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o The 64-bit timestamp value of the most recently accepted Proxy
Binding Update request sent for this mobile node. This is
obtained from the Timestamp option, present in the request.
5.2. Supported Home Network Prefix Models
This specification supports Per-MN-Prefix model and does not support
Shared-Prefix model. As per the Per-MN-Prefix model, there will be
an unique home network prefix assigned to each mobile node and no
other node shares an address from that prefix.
The mobile node's home network prefix is always hosted on the access
link where the mobile node is anchored. Conceptually, the entire
home network prefix follows the mobile node as it moves within the
Proxy Mobile IPv6 domain. The local mobility anchor is not required
to perform any proxy ND operations [RFC-2461] for defending the
mobile node's home address on the home link. However, from the
routing perspective, the home network prefix is topologically
anchored on the local mobility anchor.
5.3. Signaling Considerations
Processing Binding Registrations
Upon receiving a Proxy Binding Update request from a mobile access
gateway on behalf of a mobile node, the local mobility anchor MUST
process the request as defined in Section 10.3 [RFC-3775], with one
exception that this request is a proxy binding registration request
and hence the following additional considerations must be applied.
o The local mobility anchor MUST observe the rules described in
Section 9.2 [RFC-3775] when processing Mobility Headers in the
received Proxy Binding Update request.
o The local mobility anchor MUST identify the mobile node from the
identifier present in the NAI option [RFC-4283] of the Proxy
Binding Update request. If the NAI option is not present in the
Proxy Binding Update request, the local mobility anchor MUST
reject the request and send a Proxy Binding Acknowledgement
message with Status field set to MISSING_MN_IDENTIFIER_OPTION
(Missing mobile node identifier).
o If the local mobility anchor cannot identify the mobile node, from
the NAI option [RFC-4283] present in the request, it MUST reject
the Proxy Binding Update request and send a Proxy Binding
Acknowledgement message with Status field set to 133 (Not home
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agent for this mobile node).
o If the local mobility anchor determines that the mobile node is
not authorized for network-based mobility management service, it
MUST reject the request and send a Proxy Binding Acknowledgement
message with Status field set to PROXY_REG_NOT_ENABLED (Proxy
Registration not enabled).
o The local mobility anchor MUST ignore the check, specified in
Section 10.3.1 [RFC-3775], related to the presence of Home Address
destination option in the Proxy Binding Update request.
o The local mobility anchor MUST authenticate the Proxy Binding
Update request as described in Section 4.0. It MUST use the SPI
in the IPSec header [RFC-4306] of the received packet for locating
the security association needed for authenticating the Proxy
Binding Update request.
o The local mobility anchor MUST apply the required policy checks,
as explained in Section 4.0, to verify the sender is a trusted
mobile access gateway, authorized to send proxy binding
registration requests on behalf of this mobile node.
o If the local mobility anchor determines that the requesting node
is not authorized to send proxy binding registration requests, it
MUST reject the Proxy Binding Update request and send a Proxy
Binding Acknowledgement message with Status field set to
MAG_NOT_AUTHORIZED_FOR_PROXY_REG (Not authorized to send proxy
registrations).
o If the Home Network Prefix option is not present in the Proxy
Binding Update request, the local mobility anchor MUST reject the
Proxy Binding Update request and send a Proxy Binding
Acknowledgement message with Status field set to 129
(Administratively Prohibited).
o The local mobility anchor MUST apply the considerations specified
in Section 5.4, for processing the Sequence Number field and the
Timestamp option, in the Proxy Binding Update request.
o The local mobility anchor MUST use the identifier in the NAI
option [RFC-4283] present in the Proxy Binding Update request for
performing the Binding Cache entry existence test. If the entry
does not exist, the local mobility MUST consider this request as
an initial binding registration request.
Initial Binding Registration:
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o If the Home Network Prefix option present in the Proxy Binding
Update request has the value 0::/0, the local mobility anchor MUST
allocate a prefix for the mobile node and send a Proxy Binding
Acknowledgement message including the Home Network Prefix option
containing the allocated prefix value. The specific details on
how the local mobility anchor allocates the home network prefix is
outside the scope of this document. The local mobility anchor
MUST ensure the allocated prefix is not in use by any other mobile
node.
o If the local mobility anchor is unable to allocate a home network
prefix for the mobile node, it MUST reject the request and send a
Proxy Binding Acknowledgement message with Status field set to 130
(Insufficient resources).
o If the Home Network Prefix option present in the request has a
specific prefix hint, the local mobility anchor before accepting
that request, MUST ensure the prefix is owned by the local
mobility anchor and further the mobile node is authorized to use
that prefix. If the mobile node is not authorized to use that
prefix, the local mobility anchor MUST reject the request and send
a Proxy Binding Acknowledgement message with Status field set to
NOT_AUTHORIZED_FOR_HOME_NETWORK_PREFIX (Mobile node not authorized
to use that prefix).
o Upon accepting the request, the local mobility anchor MUST create
a Binding Cache entry for the mobile node. It must set the fields
in the Binding Cache entry to the accepted values for that
binding. If there is a Link-local Address option present in the
request, the address must be copied to the link-local address
field in the Binding Cache entry.
o Upon accepting the Proxy Binding Update request, the local
mobility anchor MUST establish a bi-directional tunnel to the
mobile access gateway, as described in [RFC-2473]. Considerations
from Section 5.5 must be applied.
Binding Re-Registration:
o If the requesting prefix in the Home Network Prefix option is a
non 0::/0 value and is different from what is present in the
currently active Binding Cache entry for that mobile node, the
local mobility anchor MUST reject the request and send a Proxy
Binding Acknowledgement message with Status field set to 129
(Administratively Prohibited).
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o Upon accepting a Proxy Binding Update request for extending the
lifetime of a currently active binding for a mobile node, the
local mobility anchor MUST update the existing Binding Cache entry
for this mobile node. Unless there exists an established bi-
directional tunnel to the mobile access gateway with the same
transport and encapsulation mode, the local mobility anchor MUST
create a tunnel to the mobile access gateway, as described in
[RFC-2473] and also delete the existing tunnel route to the
previous mobile access gateway. It MUST also send a Proxy Binding
Acknowledgement message to the mobile access gateway with the
Status field set to 0 (Proxy Binding Update Accepted).
Binding De-Registration:
o If the received Proxy Binding Update request with the lifetime
value of 0, has a Source Address in the IPv6 header, different
from what is present in the Proxy-CoA address field in its Binding
Cache entry, the local mobility anchor MAY either choose to ignore
the request or send a valid Proxy Binding Acknowledgement message
with the Status field set to 0 (Proxy Binding Update Accepted).
o Upon accepting the Proxy Binding Update request for a mobile node,
with the lifetime value of zero, the local mobility anchor MUST
wait for MinDelayBeforeBCEDelete amount of time, before it deletes
the mobile node's Binding Cache entry. Within this wait period,
if the local mobility anchor receives a Proxy Binding Update
request message for the same mobile node and from a different
mobile access gateway, with the lifetime value of greater than
zero, and if that request is accepted, then the Binding Cache
entry MUST NOT be deleted, but must be updated with the new
values. However, the local mobile anchor MUST send the Proxy
Binding Acknowledgement message, immediately upon accepting the
request.
o Upon accepting the request, the local mobility anchor MUST delete
the mobile node's Binding Cache entry and remove the Routing state
for the mobile node's home network prefix.
Constructing the Proxy Binding Acknowledgement Message:
o The local mobility anchor when sending the Proxy Binding
Acknowledgement message to the mobile access gateway MUST
construct the message as specified below.
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IPv6 header (src=LMAA, dst=Proxy-CoA)
Mobility header
-BA /*P flag is set*/
Mobility Options
- Home Network Prefix Option
- Link-local Address Option (optional)
- Timestamp Option (optional)
- NAI Option
Proxy Binding Acknowledgement message format
o The Source Address field in the IPv6 header of the message SHOULD
be set to the destination address of the received Proxy Binding
Update request.
o The Destination Address field in the IPv6 header of the message
SHOULD be set to the source address of the received Proxy Binding
Update request.
o If the Status field is set to a value greater less than 128, i.e.
if the binding request was rejected, then the prefix value in the
Home Network Prefix option MUST be set to the prefix value from
the received Home Network Prefix option. For all other cases, the
prefix value MUST be set to the allocated prefix value for that
mobile node.
o The Link-local Address option MUST be present in the Proxy Binding
Acknowledgement message, if the same option was present in the
corresponding Proxy Binding Update request message. If there is
an existing Binding Cache entry for that mobile node with the
link-local address value of ALL_ZERO (value not set), or if there
was no existing Binding Cache entry, then the link-local address
MUST be copied from the received Link-local Address option in the
received Proxy Binding Update request. For all other cases, it
MUST be copied from the Binding Cache entry.
o Considerations from Section 5.4 must be applied for constructing
the Timestamp option.
o The identifier in the NAI option [RFC-4283] MUST be copied from
the received Proxy Binding Update request. If the Status field
value is set to MISSING_MN_IDENTIFIER_OPTION, the NAI option MUST
NOT be present in the reply message.
o The message MUST be protected by using IPsec, using the security
association existing between the local mobility anchor and the
mobile access gateway.
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o The Type 2 Routing header, MUST NOT be present in the IPv6 header
of the packet.
5.4. Timestamp Option for Message Ordering
Mobile IPv6 [RFC-3775] uses the Sequence Number field in binding
registration messages as a way for the home agent to process the
binding updates in the order they were sent by a mobile node. The
home agent and the mobile node are required to manage this counter
over the lifetime of a binding. However, in Proxy Mobile IPv6, as
the mobile node moves from one mobile access gateway to another and
in the absence of context transfer mechanism, the serving mobile
access gateway will be unable to determine the sequence number that
it needs to use in the signaling messages. Hence, the sequence
number scheme as specified in [RFC-3775], will be insufficient for
Proxy Mobile IPv6.
If the local mobility anchor cannot determine the sending order of
the received binding registration messages, it may potentially
process an older message sent by a mobile access gateway, where the
mobile node was previously anchored, resulting in an incorrect
Binding Cache entry.
For solving this problem, this specification RECOMMENDS the use of
Timestamp option [Section 8.4]. The basic principle behind the use
of timestamps in binding registration messages is that the node
generating the message inserts the current time-of-day, and the node
receiving the message checks that this timestamp is greater than all
previously accepted timestamps.
Alternatively, the specification also allows the use of Sequence
Number based scheme, as per [RFC-3775]. The sequence number MUST be
maintained on a per mobile node basis and MUST be synchronized
between the serving mobile access gateways. However, the specific
details on how a mobile node's sequence number is synchronized
between different mobile access gateways is outside the scope of this
document.
Using Timestamps based approach:
o An implementation MUST support Timestamp option. If the Timestamp
option is present in the received Proxy Binding Update request
message, then the local mobility anchor MUST include a valid
Timestamp option in the Proxy Binding Acknowledgement message that
it sends to the mobile access gateway.
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o All the mobility entities in a Proxy Mobile IPv6 domain,
exchanging binding registration messages using Timestamp option
must have adequately synchronized time-of-day clocks. These nodes
SHOULD synchronize their clocks to a common time source, using
Network Time Protocol [RFC-4330] or in any other ways suitable for
that specific deployment.
o When generating the timestamp value for building the Timestamp
option, the mobility entities MUST ensure that the generated
timestamp is the elapsed time past the same reference epoch, as
specified in the format for the Timestamp option [Section 8.5].
o Upon receipt of a Proxy Binding Update message with the Timestamp
option, the local mobility anchor MUST check the timestamp field
for validity. In order for it to be considered valid, the
timestamp value contained in the Timestamp option MUST be close
enough to the local mobility anchor's time-of-day clock and the
timestamp MUST be greater than all previously accepted timestamps
in the Proxy Binding Update messages sent for that mobile node.
o If the Timestamp option is present in the received Proxy Binding
Update message, the local mobility anchor MUST ignore the sequence
number field in the message. However, it MUST copy the sequence
number from the received Proxy Binding Update message to the Proxy
Binding Acknowledgement message.
o If the timestamp value in the received Proxy Binding Update is
valid, the local mobility anchor MUST return the same timestamp
value in the Timestamp option included in the Proxy Binding
Acknowledgement message that it sends to the mobile access
gateway.
o If the timestamp value in the received Proxy Binding Update is not
valid, the local mobility anchor MUST reject the Proxy Binding
Update and send a Proxy Binding Acknowledgement message with
Status field set to TIMESTAMP_MISMATCH (Timestamp mismatch). The
message MUST also include the Timestamp option with the value set
to the current time-of-day on the local mobility anchor.
Using Sequence Number based approach:
o If the Timestamp option is not present in the received Proxy
Binding Update request, the local mobility anchor MUST fallback to
the Sequence Number based scheme. It MUST process the sequence
number field as specified in [RFC-3775]. Also, it MUST NOT
include the Timestamp option in the Proxy Binding Acknowledgement
messages that it sends to the mobile access gateway.
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5.5. Routing Considerations
5.5.1. Bi-Directional Tunnel Management
o A bi-directional tunnel is established between the local mobility
anchor and the mobile access gateway with IP-in-IP encapsulation,
as described in [RFC-2473]. The tunnel end points are the Proxy-
CoA and LMAA. When using IPv4 transport with a specific
encapsulation mode, the end points of the tunnel are the IPv4-LMAA
and IPv4-Proxy-CoA, as specified in [ID-IPV4-PMIP6].
o The bi-directional tunnel is used for routing the mobile node's
data traffic between the mobile access gateway and the local
mobility anchor. The tunnel hides the topology and enables a
mobile node to use an address from its home network prefix from
any access link attached to the mobile access gateway.
o The bi-directional tunnel is established after accepting the Proxy
Binding Update request message. The created tunnel may be shared
with other mobile nodes attached to the same mobile access gateway
and with the local mobility anchor having a Binding Cache entry
for those mobile nodes. Implementations MAY choose to use static
tunnels as supposed to dynamically creating and tearing them down
on a need basis.
o The tunnel between the local mobility anchor and the mobile access
gateway is typically a shared tunnel and can be used for routing
traffic streams for different mobile nodes attached to the same
mobile access gateway.
o Implementations typically use a software timer for managing the
tunnel lifetime and a counter for keeping a count of all the
mobile nodes that are sharing the tunnel. The timer value will be
set to the accepted binding life-time and will be updated after
each periodic registrations for extending the lifetime. If the
tunnel is shared for multiple mobile nodes, the tunnel lifetime
will be set to the highest binding lifetime that is granted to any
one of those mobile nodes sharing that tunnel.
5.5.2. Forwarding Considerations
Intercepting Packets Sent to the Mobile Node's Home Network:
o When the local mobility anchor is serving a mobile node, it MUST
be able to receive packets that are sent to the mobile node's home
network. In order for it to receive those packets, it MUST
advertise a connected route in to the Routing Infrastructure for
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the mobile node's home network prefix or for an aggregated prefix
with a larger scope. This essentially enables IPv6 routers in
that network to detect the local mobility anchor as the last-hop
router for that prefix.
Forwarding Packets to the Mobile Node:
o On receiving a packet from a corresponding node with the
destination address matching a mobile node's home network prefix,
the local mobility anchor MUST forward the packet through the bi-
directional tunnel setup for that mobile node. The format of the
tunneled packet is shown below. However, when using IPv4
transport, the format of the packet is as described in [ID-IPV4-
PMIP6].
IPv6 header (src= LMAA, dst= Proxy-CoA /* Tunnel Header */
IPv6 header (src= CN, dst= MN-HOA ) /* Packet Header */
Upper layer protocols /* Packet Content*/
Figure 7: Tunneled Packets from LMA to MAG
Forwarding Packets Sent by the Mobile Node:
o All the reverse tunneled packets that the local mobility anchor
receives from the mobile access gateway, after removing the tunnel
header MUST be routed to the destination specified in the inner
packet header. These routed packets will have the source address
field set to the mobile node's home address.
5.6. Local Mobility Anchor Address Discovery
Dynamic Home Agent Address Discovery, as explained in Section 10.5
[RFC-3775], allows a mobile node to discover all the home agents on
its home link by sending an ICMP Home Agent Address Discovery Request
message to the Mobile IPv6 Home-Agents anycast address, derived from
its home network prefix.
The DHAAD message in the current form cannot be used in Proxy Mobile
IPv6 for discovering the address of the mobile node's local mobility
anchor. In Proxy Mobile IPv6, the local mobility anchor will not be
able to receive any messages sent to the Mobile IPv6 Home-Agents
anycast address corresponding to the mobile node's home network
prefix, as the prefix is not hosted on any of its interfaces.
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Further, the mobile access gateway will not predictably be able to
locate the serving local mobility anchor that has the mobile node's
binding cache entry. Hence, this specification does not support
Dynamic Home Agent Address Discovery protocol.
In Proxy Mobile IPv6, the address of the local mobility anchor
configured to serve a mobile node can be discovered by the mobility
entities in other ways. This may be a configured entry in the mobile
node's policy profile, or it may be obtained through mechanisms
outside the scope of this document.
5.7. Mobile Prefix Discovery Considerations
The ICMP Mobile Prefix Advertisement message, described in Section
6.8 and Section 11.4.3 of [RFC-3775], allows a home agent to send a
Mobile Prefix Advertisement to the mobile node.
In Proxy Mobile IPv6, the mobile node's home network prefix is hosted
on the access link connected to the mobile access gateway. but it is
topologically anchored on the local mobility anchor. Since, there is
no physical home-link for the mobile node's home network prefix on
the local mobility anchor and as the mobile node is always on the
link where the prefix is hosted, any prefix change messages can just
be advertised by the mobile access gateway on the access link and
thus there is no applicability of this message for Proxy Mobile IPv6.
Hence, this specification does not support Mobile Prefix Discovery.
5.8. Route Optimizations Considerations
The Route Optimization in Mobile IPv6, as defined in [RFC-3775],
enables a mobile node to communicate with a corresponding node
directly using its care-of address and further the Return Routability
procedure enables the corresponding node to have reasonable trust
that the mobile node is reachable at both its home address and
care-of address.
In Proxy Mobile IPv6, the mobile node is not involved in any mobility
related signaling. The mobile node uses only its home address for
all its communication and the Care-of address (Proxy-CoA) is not
visible to the mobile node. Hence, the Return Routability procedure
as defined in Mobile IPv6 cannot be used in Proxy Mobile IPv6.
6. Mobile Access Gateway Operation
The Proxy Mobile IPv6 protocol described in this document, introduces
a new functional entity, the Mobile Access Gateway (MAG). The mobile
access gateway is the entity that is responsible for detecting the
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mobile node's movements on its access link and sending the binding
registration requests to the local mobility anchor. In essence, the
mobile access gateway performs mobility management on behalf of a
mobile node.
The mobile access gateway is a function that typically runs on an
access router. However, implementations MAY choose to split this
function and run it across multiple systems. The specifics on how
that is achieved or the signaling interactions between those
functional entities is beyond the scope of this document.
The mobile access gateway has the following key functional roles:
o It is responsible for detecting the mobile node's movements on the
access link and for initiating the mobility signaling with the
mobile node's local mobility anchor.
o Emulation of the mobile node's home link on the access link by
sending Router Advertisements with the mobile node's home network
prefix information.
o Responsible for setting up the data path for enabling the mobile
node to configure an address from its home network prefix and use
it from its access link.
6.1. Extensions to Binding Update List Entry Data Structure
Every mobile access gateway MUST maintain a Binding Update List.
Each entry in the Binding Update List represents a mobile node's
mobility binding with its local mobility anchor. The Binding Update
List is a conceptual data structure, described in Section 11.1 [RFC-
3775].
For supporting this specification, the conceptual Binding Update List
entry data structure needs be extended with the following additional
fields.
o The Identifier of the attached mobile node, MN-Identifier. This
identifier is acquired during the mobile node's attachment to the
access link or through mechanisms outside the scope of this
document.
o The Link-layer address of the mobile node. This address can be
acquired from the received Router Solicitation messages from the
mobile node or during the mobile node's attachment to the access
network.
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o The IPv6 home network prefix of the attached mobile node. The
home network prefix of the mobile node is acquired from the mobile
node's local mobility anchor through the received Proxy Binding
Acknowledgement messages. The IPv6 home network prefix also
includes the corresponding prefix length.
o The Link-local address of the mobile node on the interface
attached to the access link.
o The IPv6 address of the local mobility anchor serving the attached
mobile node. This address is acquired from the mobile node's
policy profile.
o The interface identifier of the access link where the mobile node
is currently attached. The interface identifier is acquired
during the mobile node's attachment to the access link.
o The interface identifier of the bi-directional tunnel between the
mobile node's local mobility anchor and the mobile access gateway.
The tunnel interface identifier is acquired during the tunnel
creation.
6.2. Mobile Node's Policy Profile
A mobile node's policy profile contains the essential operational
parameters that are required by the network entities for managing the
mobile node's mobility service. These policy profiles are stored in
a local or a remote policy store, the mobile access gateway and the
local mobility anchor MUST be able to obtain a mobile node's policy
profile. The policy profile may also be handed over to a serving
mobile access gateway as part of a context transfer procedure during
a handoff. The exact details on how this achieved is outside the
scope of this document. However, this specification requires that a
mobile access gateway serving a mobile node MUST have access to its
policy profile.
The following are the mandatory fields of the policy profile:
o The mobile node's identifier (MN-Identifier)
o The IPv6 address of the local mobility anchor (LMAA)
o Supported address configuration procedures on the link (Stateful,
Stateless or both)
The following are the optional fields of the policy profile:
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o The mobile node's IPv6 home network prefix (MN-HNP)
6.3. Supported Access Link Types
This specification supports only point-to-point access link types and
thus it assumes that the mobile node and the mobile access gateway
are the only two nodes on the access link. The link is assumed to
have multicast capability.
6.4. Supported Address Configuration Models
A mobile node in the Proxy Mobile IPv6 domain can configure one or
more IPv6 addresses on its interface using Stateless or Stateful
address autoconfiguration procedures. The Router Advertisement
messages sent on the access link, specify the address configuration
methods permitted on that access link for that mobile node. However,
the advertised flags with respect the address configuration will be
consistent for a mobile node, on any of the access links in that
Proxy Mobile IPv6 domain. Typically, these configuration settings
will be based on the domain wide policy or based on a policy specific
to each mobile node.
When stateless address autoconfiguration is supported on the link,
the mobile node can generate one or more IPv6 addresses by combining
the network prefix advertised on the access link with an interface
identifier, using the techniques described in Stateless
Autoconfiguration specification [RFC-2462] or as per Privacy
extension specification [RFC-3041].
When stateful address autoconfiguration is supported on the link, the
mobile node can obtain the address configuration from the DHCPv6
server using DHCPv6 client protocol, as specified in DHCPv6
specification [RFC-3315].
Additionally, other address configuration mechanisms specific to the
access link between the mobile node and the mobile access gateway may
also be used for pushing the address configuration to the mobile
node.
6.5. Access Authentication & Mobile Node Identification
When a mobile node attaches to an access link connected to the mobile
access gateway, the deployed access security protocols on that link
SHOULD ensure that the network-based mobility management service is
offered only after authenticating and authorizing the mobile node for
that service. The exact specifics on how this is achieved or the
interactions between the mobile access gateway and the access
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security service is outside the scope of this document. This
specification goes with the stated assumption of having an
established trust between the mobile node and mobile access gateway,
before the protocol operation begins.
6.6. Acquiring Mobile Node's Identifier
All the network entities in a Proxy Mobile IPv6 domain MUST be able
to identify a mobile node, using its MN-Identifier. This identifier
MUST be stable across the Proxy Mobile IPv6 domain and the entities
must be able to use this identifier in the signaling messages.
Typically, this identifier is obtained as part of the access
authentication or through other means as specified below.
o The identifier of the mobile node that the mobile access gateway
obtains as part of the access authentication or from the notified
network attachment event, can be a temporary identifier and this
identifier may also change at each re-authentication. However,
the mobile access gateway MUST be able to authenticate the mobile
node based on this identifier and MUST be able to obtain the MN-
Identifier from the policy store, such as from the RADIUS
attribute, Chargeable-User-Identifier.
o The MN-Identifier that the policy store delivers to the mobile
access gateway may not be the true identifier of the mobile node.
However, the mobility access gateway MUST be able to use this
identifier in the signaling messages exchanged with the local
mobility anchor.
o The mobile access gateway MUST be able identify the mobile node by
its MN-Identifier and it MUST be able to associate this identity
to the sender of any IPv4 or IPv6 packets on the access link.
6.7. Home Network Emulation
One of the key functions of a mobile access gateway is to emulate the
mobile node's home network on the access link. It must ensure, the
mobile node believes it is still connected to its home link or on the
link where it obtained its initial address configuration after it
moved into that Proxy Mobile IPv6 domain.
For emulating the mobile node's home link on the access link, the
mobile access gateway must be able to send Router Advertisements
advertising the mobile node's home network prefix and other address
configuration parameters consistent with its home link properties.
Typically, the mobile access gateway learns the mobile node's home
network prefix information from the received Proxy Binding
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Acknowledgement message or it may be obtained from the mobile node's
policy profile. However, the mobile access gateway SHOULD send the
Router Advertisements advertising the mobile node's home network
prefix only after successfully completing the binding registration
with the mobile node's local mobility anchor.
6.8. Link-Local and Global Address Uniqueness
A mobile node in the Proxy Mobile IPv6 domain, as it moves from one
mobile access gateway to the other, it will continue to detect its
home network and thus making it believe it is still on the same link.
Every time the mobile node attaches to a new link, the event related
to the interface state change, will trigger the mobile node to
perform DAD operation on the link-local and global addresses.
However, if the mobile node is DNAv6 enabled, as specified in [ID-
DNAV6], it may not detect the link change due to DNAv6 optimizations
and may not trigger the duplicate address detection (DAD) procedure
for establishing the link-local address uniqueness on that new link.
Further, if the mobile node uses an interface identifier that is not
based on EUI-64 identifier, such as specified in IPv6 Stateless
Autoconfiguration specification [RFC-2462], there is a possibility,
with the odds of 1 to billion, of a link-local address collision
between the two neighbors on that access link.
One of the workarounds for this issue is to set the DNAv6
configuration parameter, DNASameLinkDADFlag to TRUE and that will
force the mobile node to redo DAD operation every time the interface
detects a handover, even when DNAv6 does not detect a link change.
However, this issues will not impact point-to-point links based on
PPP session. Each time the mobile node moves and attaches to a new
mobile access gateway, either the PPP session [RFC-1661] is
reestablished or the PPP session may be moved as part of context
transfer procedures between the old and the new mobile access
gateway.
When the mobile node tries to establish a PPP session with the mobile
access gateway, the PPP goes through the Network layer Protocol phase
and the IPv6 Control Protocol, IPCP6 [RFC-2472] gets triggered. Both
the PPP peers negotiate a unique identifier using Interface-
Identifier option in IPV6CP and the negotiated identifier is used for
generating a unique link-local address on that link. Now, if the
mobile node moves to a new mobile access gateway, the PPP session
gets torn down with the old mobile access gateway and a new PPP
session gets established with the new mobile access gateway, and the
mobile node obtains a new link-local address. So, even if the mobile
node is DNAv6 capable, the mobile node always configures a new link-
local address when ever it moves to a new link.
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If the PPP session state is moved to the new mobile access gateway,
as part of context transfer procedures that are in place, there will
not be any change to the interface identifiers of the two nodes on
that point-to-point change. The whole link is moved to the new
mobile access gateway and there will not be any need for establishing
link-local address uniqueness on that link.
Alternatively, this specification allows the mobile access gateway to
upload the mobile node's link-local address to the local mobility
anchor using the Link-local Address option, exchanged in the binding
registration messages. The mobile access gateway can learn the
mobile node's link-local address, by snooping the DAD messages sent
by the mobile node for establishing the link-local address uniqueness
on the access link. Subsequently, at each handoff, the mobile access
gateway can obtain this address from the local mobility anchor and
can change its own link-local address, if it detects an address
collision.
This issue is not relevant to the mobile node's global address.
Since, there is a unique home network prefix for each mobile node,
the uniqueness for the mobile node's global address is assured on the
access link.
6.9. Signaling Considerations
6.9.1. Binding Registrations
Initial Binding Registration:
o After detecting a new mobile node on its access link, the mobile
access gateway must identify the mobile node and acquire its MN-
Identifier. If it determines that the network-based mobility
management service needs to offered to the mobile node, it MUST
send a Proxy Binding Update message to the local mobility anchor.
o The Proxy Binding Update message MUST have the NAI option [RFC-
4283], identifying the mobile node, the Home Network Prefix
option, Timestamp option or a valid sequence number and optionally
the Link-local Address option.
o If the mobile access gateway learns the mobile node's home network
prefix either from its policy store or from other means, the
mobile access gateway MAY choose to specify the same in the Home
Network Prefix option for requesting the local mobility anchor to
allocate that prefix. If the specified value is 0::/0, then the
local mobility anchor will consider this as a request for prefix
allocation.
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Receiving Binding Registration Reply:
o The mobile access gateway MUST observe the rules described in
Section 9.2 [RFC-3775] when processing Mobility Headers in the
received Proxy Binding Acknowledgement message.
o The message MUST be authenticated as described in Section 4.0.
The SPI in the IPSec header [RFC-4306] of the received packet must
be used for locating the security association needed for
authenticating the message.
o The mobile access gateway MUST apply the considerations specified
in Section 5.4, for processing the Sequence Number field and the
Timestamp option, in the message.
o The mobile access gateway MUST ignore any checks, specified in
[RFC-3775] related to the presence of Type 2 Routing header in the
Proxy Binding Acknowledgement message.
o If the received Proxy Binding Acknowledgement message has the
Status field value set to PROXY_REG_NOT_ENABLED (Proxy
registration not enabled for the mobile node), the mobile access
gateway SHOULD not send binding registration requests again for
that mobile node. It must also deny the mobility service to that
mobile node.
o If the received Proxy Binding Acknowledgement message has the
Status field value set to TIMESTAMP_MISMATCH (Invalid Timestamp),
the mobile access gateway SHOULD try to register again only after
it synchronized its clock with the local mobility anchor's system
clock or to a common time source that is used by all mobility
entities in that domain for their clock synchronization.
o If the received Proxy Binding Acknowledgement message has the
Status field value set to NOT_AUTHORIZED_FOR_HOME_NETWORK_PREFIX
(Not authorized for that prefix), the mobile access gateway SHOULD
try to request for that prefix in the binding registration
request, only after it learned the validity of that prefix.
o If the received Proxy Binding Acknowledgement message has the
Status field value set to any value greater than 128 (i.e., the
binding is rejected), the mobile access gateway MUST NOT advertise
the mobile node's home network prefix in the Router Advertisements
sent on that access link and there by denying mobility service to
the mobile node.
o If the received Proxy Binding Acknowledgement message has the
Status field value set to 0 (Proxy Binding Update accepted), the
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mobile access gateway MUST create Binding Update List entry for
the mobile node and must setup a tunnel to the mobile node's local
mobility anchor, as explained in section 6.10.
o If the received Proxy Binding Acknowledgement message has the
address in the Link-local Address option set to a value that
matches its own link-local address on that access interface where
the mobile node is anchored, the mobile access gateway MUST change
its link-local address on that interface.
Binding Re-Registration:
o For extending the lifetime of a currently existing binding at the
local mobility, the mobile access gateway MUST send a Proxy
Binding Update message to the local mobility anchor. The prefix
value in the Home Network Prefix option present in the request
SHOULD be set to the currently registered home network prefix and
the value in the Link-local Address option may be set to ALL_ZERO
or to the link-local address of the mobile node.
Binding De-Registration:
o At any point, the mobile access gateway detects that the mobile
node has moved away from its access link, it MUST send a Proxy
Binding Update message to the local mobility anchor with the
lifetime value set to zero.
o Either upon receipt of a Proxy Binding Acknowledgement message
from the local mobility anchor or after a certain timeout waiting
for the reply, the mobile access gateway MUST remove the binding
entry for that mobile node from its Binding Update List and
withdraw the mobile node's home network prefix as the hosted on-
link prefix on that access link.
Constructing the Proxy Binding Update Message:
o The mobile access gateway when sending the Proxy Binding Update
request to the local mobility anchor MUST construct the message as
specified below.
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IPv6 header (src=Proxy-CoA, dst=LMAA)
Mobility header
-BU /*P & A flags are set*/
Mobility Options
- Home Network Prefix option
- Link-local Address option (Optional)
- Timestamp Option (optional)
- NAI Option
Proxy Binding Update message format
o The Source Address field in the IPv6 header of the message SHOULD
be set to the address of the mobile access gateway.
o The Destination Address field in the IPv6 header of the message
SHOULD be set to the local mobility anchor address.
o The Home Network Prefix option MUST be present. The prefix value
may be set 0::/0 or to a specific prefix value.
o The Link-local Address option MAY be present. The value may be
set to ALL_ZERO or the mobile node's link-local address.
o Considerations from Section 5.4 must be applied for constructing
the Timestamp option.
o The NAI option [RFC-4283] MUST be present, the identifier field in
the option MUST be set to mobile node's identifier, MN-Identifier.
o The message MUST be protected by using IPsec, using the security
association existing between the local mobility anchor and the
mobile access gateway.
6.9.2. Router Solicitation Messages
The mobile node sends a Router Solicitation message on the access
link when ever the link-layer detects a media change. The Source
Address in the IPv6 header of the Router Solicitation message may
either be the link-local address of the mobile node or an unspecified
address (::).
o The mobile access gateway on receiving the Router Solicitation
message SHOULD send a Router Advertisement containing the mobile
node's home network prefix as the on-link prefix. However, before
sending the Router Advertisement message containing the mobile
node's home network prefix, it SHOULD complete the binding
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registration process with the mobile node's local mobility anchor.
o If the local mobility anchor rejects the binding registration
request, or, if the mobile access gateway failed to complete the
binding registration process for what ever reasons, the mobile
access gateway MUST NOT advertise the mobile node's home network
prefix in the Router Advertisement messages that it sends on the
access link. However, it MAY choose to advertise a local visitor
network prefix to enable the mobile node for simple IPv6 access.
6.9.3. Retransmissions and Rate Limiting
The mobile access gateway is responsible for retransmissions and rate
limiting the binding registration requests that it sends for updating
a mobile node's binding. Implementations MUST follow the below
guidelines.
o When the mobile access gateway sends a Proxy Binding Update
request, it should use the constant, INITIAL_BINDINGACK_TIMEOUT
[RFC-3775], for configuring the retransmission timer.
o If the mobile access gateway fails to receive a valid matching
response within the retransmission interval, it SHOULD retransmit
the message until a response is received.
o As specified in Section 11.8 [RFC-3775], the mobile access gateway
MUST use an exponential back-off process in which the timeout
period is doubled upon each retransmission, until either the node
receives a response or the timeout period reaches the value
MAX_BINDACK_TIMEOUT [RFC-3775]. The mobile access gateway MAY
continue to send these messages at this slower rate indefinitely.
o If Timestamp based scheme is in use, the retransmitted Proxy
Binding Update messages MUST use the latest timestamp. If
Sequence number scheme is in use, the retransmitted Proxy Binding
Update messages MUST use a Sequence Number value greater than that
used for the previous transmission of this Proxy Binding Update
message, just as specified in [RFC-3775].
6.10. Routing Considerations
This section describes how the mobile access gateway handles the
traffic to/from the mobile node that is attached to one of its access
interface.
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Proxy-CoA LMAA
| |
+--+ +---+ +---+ +--+
|MN|----------|MAG|======================|LMA|----------|CN|
+--+ +---+ +---+ +--+
IPv6 Tunnel
6.10.1. Transport Network
The transport network between the local mobility anchor and the
mobile access can be either an IPv6 or IPv4 network. However, this
specification only deals with the IPv6 transport and the companion
document [ID-IPV4-PMIP6] specifies the required extensions for
negotiating IPv4 transport and the corresponding encapsulation mode,
for supporting this protocol operation.
6.10.2. Tunneling & Encapsulation Modes
The IPv6 address that a mobile node uses from its home network prefix
is topologically anchored at the local mobility anchor. For a mobile
node to use this address from an access network attached to a mobile
access gateway, proper tunneling techniques have to be in place.
Tunneling hides the network topology and allows the mobile node's
IPv6 datagrams to be encapsulated as a payload of another IPv6 packet
and be routed between the local mobility anchor and the mobile access
gateway. The Mobile IPv6 base specification [RFC-3775] defines the
use of IPv6-over-IPv6 tunneling, between the home agent and the
mobile node and this specification extends the use of the same
tunneling mechanism between the local mobility anchor and the mobile
access gateway.
On most operating systems, tunnels are implemented as a virtual
point-to-point interface. The source and the destination address of
the two end points of this virtual interface along with the
encapsulation mode are specified for this virtual interface. Any
packet that is routed over this interface, get encapsulated with the
outer header and the addresses as specified for that point to point
tunnel interface. For creating a point to point tunnel to any local
mobility anchor, the mobile access gateway may implement a tunnel
interface with the source address field set to its Proxy-CoA address
and the destination address field set to the LMA address.
The following are the supported packet encapsulation modes that can
be used by the mobile access gateway and the local mobility anchor
for routing mobile node's IPv6 datagrams.
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o IPv6-In-IPv6 - IPv6 datagram encapsulated in an IPv6 packet. This
mechanism is defined in the Generic Packet Tunneling for IPv6
specification [RFC-2473].
o IPv6-In-IPv4 - IPv6 datagram encapsulation in an IPv4 packet. The
details related to this encapsulation mode and the specifics on
how this mode is negotiated is specified in the companion
document, IPv4 support for Proxy Mobile IPv6 [ID-IPV4-PMIP6].
o IPv6-In-IPv4-UDP - IPv6 datagram encapsulation in an IPv4 UDP
packet. The details related to this mode are covered in the
companion document, IPv4 support for Proxy Mobile IPv6 [ID-IPV4-
PMIP6].
6.10.3. Routing State
The following section explains the routing state for a mobile node on
the mobile access gateway. This routing state reflects only one
specific way of implementation and one MAY choose to implement it in
other ways. The policy based route defined below acts as a traffic
selection rule for routing a mobile node's traffic through a specific
tunnel created between the mobile access gateway and that mobile
node's local mobility anchor and with the specific encapsulation
mode, as negotiated.
The below example identifies the routing state for two visiting
mobile nodes, MN1 and MN2 with their respective local mobility
anchors LMA1 and LMA2.
For all traffic from the mobile node, identified by the mobile node's
MAC address, ingress interface or source prefix (MN-HNP) to
_ANY_DESTINATION_ route via interface tunnel0, next-hop LMAA.
+==================================================================+
| Packet Source | Destination Address | Destination Interface |
+==================================================================+
| MAC_Address_MN1, | _ANY_DESTINATION_ | Tunnel0 |
| (IPv6 Prefix or |----------------------------------------------|
| Input Interface) | Locally Connected | Tunnel0 |
+------------------------------------------------------------------+
| MAC_Address_MN2, | _ANY_DESTINATION_ | Tunnel1 |
+ (IPv6 Prefix or -----------------------------------------------|
| Input Interface | Locally Connected | direct |
+------------------------------------------------------------------+
Example - Policy based Route Table
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+==================================================================+
| Interface | Source Address | Destination Address | Encapsulation |
+==================================================================+
| Tunnel0 | Proxy-CoA | LMAA1 | IPv6-in-IPv6 |
+------------------------------------------------------------------+
| Tunnel1 |IPv4-Proxy-CoA | IPv4-LMA2 | IPv6-in-IPv4 |
+------------------------------------------------------------------+
Example - Tunnel Interface Table
6.10.4. Local Routing
If there is data traffic between a visiting mobile node and a
corresponding node that is locally attached to an access link
connected to the mobile access gateway, the mobile access gateway MAY
optimize on the delivery efforts by locally routing the packets and
by not reverse tunneling them to the mobile node's local mobility
anchor. However, this has an implication on the mobile node's
accounting and policy enforcement as the local mobility anchor is not
in the path for that traffic and it will not be able to apply any
traffic policies or do any accounting for those flows.
This decision of path optimization SHOULD be based on the configured
policy configured on the mobile access gateway, but enforced by the
mobile node's local mobility anchor. The specific details on how
this is achieved is beyond of the scope of this document.
6.10.5. Tunnel Management
All the considerations mentioned in Section 5.5.1, for the tunnel
management on the local mobility anchor apply for the mobile access
gateway as well.
6.10.6. Forwarding Rules
Forwarding Packets sent to the Mobile Node's Home Network:
o On receiving a packet from the bi-directional tunnel established
with the mobile node's local mobility anchor, the mobile access
gateway MUST use the destination address of the inner packet for
forwarding it on the interface where the destination network
prefix is hosted. The mobile access gateway MUST remove the outer
header before forwarding the packet. If the mobile access gateway
cannot find the connected interface for that destination address,
it MUST silently drop the packet. For reporting an error in such
scenario, in the form of ICMP control message, the considerations
from Generic Packet Tunneling specification [RFC-2473] must be
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applied.
o On receiving a packet from a corresponding node that is locally
connected, to the mobile node that is on the access link, the
mobile access gateway MUST check the configuration variable,
EnableMAGLocalRouting, to ensure the mobile access gateway is
allowed to route the packet directly to the mobile node. If the
mobile access gateway is not allowed to route the packet directly,
it MUST route the packet through the bi-directional tunnel
established between itself and the mobile node's local mobility
anchor. Otherwise, it can route the packet directly to the mobile
node.
Forwarding Packets Sent by the Mobile Node:
o On receiving a packet from a mobile node connected to its access
link, the mobile access gateway MUST ensure that there is an
established binding for that mobile node with its local mobility
anchor before forwarding the packet directly to the destination or
before tunneling the packet to the mobile node's local mobility
anchor.
o On receiving a packet from a mobile node connected to its access
link, to a destination that is locally connected, the mobile
access gateway MUST check the configuration variable,
EnableMAGLocalRouting, to ensure the mobile access gateway is
allowed to route the packet directly to the destination. If the
mobile access gateway is not allowed to route the packet directly,
it MUST route the packet through the bi-directional tunnel
established between itself and the mobile node's local mobility
anchor. Otherwise, it can route the packet directly to the
destination.
o On receiving a packet from the mobile node connected to its access
link, to a destination that is not directly connected, the packet
MUST be forwarded to the local mobility anchor through the bi-
directional tunnel established between itself and the mobile
node's local mobility anchor. However, the packets that are sent
with the link-local source address MUST NOT be forwarded. The
format of the tunneled packet is shown below. However, when using
IPv4 transport, the format of the tunneled packet is as described
in [ID-IPV4-PMIP6].
IPv6 header (src= Proxy-CoA, dst= LMAA /* Tunnel Header */
IPv6 header (src= MN-HoA, dst= CN ) /* Packet Header */
Upper layer protocols /* Packet Content*/
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Figure 12: Tunneled Packets from MAG to LMA
6.11. Interaction with DHCP Relay Agent
If Stateful Address Configuration using DHCP is supported on the link
where the mobile node is attached, the DHCP relay agent [RFC-3315]
needs to be configured on that access link.
When the mobile node sends a DHCPv6 Request message, the DHCP relay
agent function on the access link will set the link-address field in
the DHCPv6 message to the mobile node's home network prefix, so as to
provide a prefix hint to the DHCP Server for the address pool
selection.
6.12. Home Network Prefix Renumbering
If the mobile node's home network prefix gets renumbered or becomes
invalid during the middle of a mobility session, the mobile access
gateway MUST withdraw the prefix by sending a Router Advertisement on
the access link with zero prefix lifetime for the mobile node's home
network prefix. Also, the local mobility anchor and the mobile
access gateway MUST delete the routing state for that prefix.
However, the specific details on how the local mobility anchor
notifies the mobile access gateway about the mobile node's home
network prefix renumbering is outside the scope of this document.
6.13. Mobile Node Detachment Detection and Resource Cleanup
Before sending a Proxy Binding Update message to the local mobility
anchor for extending the lifetime of a currently existing binding of
a mobile node, the mobile access gateway MUST make sure the mobile
node is still attached to the connected link by using some reliable
method. If the mobile access gateway cannot predictably detect the
presence of the mobile node on the connected link, it MUST NOT
attempt to extend the registration lifetime of the mobile node.
Further, in such scenario, the mobile access gateway SHOULD terminate
the binding of the mobile node by sending a Proxy Binding Update
message to the mobile node's local mobility anchor with lifetime
value set to 0. It MUST also remove any local state such as the
Binding Update List created for that mobile node.
The specific detection mechanism of the loss of a visiting mobile
node on the connected link is specific to the access link between the
mobile node and the mobile access gateway and is outside the scope of
this document. Typically, there are various link-layer specific
events specific to each access technology that the mobile access
gateway can depend on for detecting the node loss. In general, the
mobile access gateway can depend on one or more of the following
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methods for the detection presence of the mobile node on the
connected link:
o Link-layer event specific to the access technology
o PPP Session termination event on point-to-point link types
o IPv6 Neighbor Unreachability Detection event from IPv6 stack
o Notification event from the local mobility anchor
o Absence of data traffic from the mobile node on the link for a
certain duration of time
6.14. Allowing network access to other IPv6 nodes
In some proxy mobile IPv6 deployments, network operators may want to
provision the mobile access gateway to offer network-based mobility
management service only to some visiting mobile nodes and enable just
regular IPv6/IPv4 access to some other nodes attached to that mobile
access gateway. This requires the network to have the control on
when to enable network-based mobility management service to a mobile
node and when to enable regular IPv6 access. This specification does
not disallow such configuration.
Upon obtaining the mobile node's profile after a successful access
authentication and after a policy consideration, the mobile access
gateway MUST determine if the network based mobility service should
be offered to that mobile node. If the mobile node is entitled for
such service, then the mobile access gateway must ensure the mobile
node believes it is on its home link, as explained in various
sections of this specification.
If the mobile node is not entitled for the network-based mobility
management service, as enforced by the policy, the mobile access
gateway MAY choose to offer regular IPv6 access to the mobile node
and hence the normal IPv6 considerations apply. If IPv6 access is
enabled, the mobile node SHOULD be able to obtain any IPv6 address
using normal IPv6 address configuration mechanisms. The obtained
address must be from a local visitor network prefix. This
essentially ensures, the mobile access gateway functions as any other
access router and does not impact the protocol operation of a mobile
node attempting to use host-based mobility management service when it
attaches to an access link connected to a mobile access gateway in a
Proxy Mobile IPv6 domain.
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7. Mobile Node Operation
This non-normative section explains the mobile node's operation in a
Proxy Mobile IPv6 domain.
7.1. Moving into a Proxy Mobile IPv6 Domain
Once a mobile node enters a Proxy Mobile IPv6 domain and attaches to
an access network, the mobile access gateway on the access link
detects the attachment of the mobile node and completes the binding
registration with the mobile node's local mobility anchor. If the
binding update operation is successfully performed, the mobile access
gateway will create the required state and setup the data path for
the mobile node's data traffic.
If the mobile node is IPv6 enabled, on attaching to the access link,
it will typically send Router Solicitation message [RFC-2461]. The
mobile access gateway on the access link will respond to the Router
Solicitation message with a Router Advertisement. The Router
Advertisement will have the mobile node's home network prefix,
default-router address and other address configuration parameters.
If the mobile access gateway on the access link, receives a Router
Solicitation message from the mobile node, before it completed the
signaling with the mobile node's local mobility anchor, the mobile
access gateway may not know the mobile node's home network prefix and
may not be able to emulate the mobile node's home link on the access
link. In such scenario, the mobile node may notice a slight delay
before it receives a Router Advertisement message.
If the received Router Advertisement has the Managed Address
Configuration flag set, the mobile node, as it would normally do,
will send a DHCPv6 Request [RFC-3315]. The DHCP relay service
enabled on that access link will ensure the mobile node will obtain
its IPv6 address as a lease from its home network prefix.
If the received Router Advertisement does not have the Managed
Address Configuration flag set and if the mobile node is allowed to
use an autoconfigured address, the mobile node will be able to obtain
an IPv6 address using an interface identifier generated as per the
Autoconf specification [RFC-2462] or as per the Privacy Extensions
specification [RFC-3041].
If the mobile node is IPv4 enabled and if the network permits, it
will be able to obtain the IPv4 address configuration for the
connected interface by using DHCP [RFC-2131]. The details related to
IPv4 support is specified in the companion document [ID-IPV4-PMIP6].
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Once the address configuration is complete, the mobile node can
continue to use this address configuration as long as it is attached
to the network that is in the scope of that Proxy Mobile IPv6 domain.
7.2. Roaming in the Proxy Mobile IPv6 Domain
After obtaining the address configuration in the Proxy Mobile IPv6
domain, as the mobile node moves and changes its point of attachment
from one mobile access gateway to the other, it can still continue to
use the same address configuration. As long as the attached access
network is in the scope of that Proxy Mobile IPv6 domain, the mobile
node will always detect the same link, where it obtained its initial
address configuration. If the mobile node performs DHCP operation,
it will always obtain the same address as before.
However, the mobile node will always detect a new default-router on
each connected link, but still advertising the mobile node's home
network prefix as the on-link prefix and with the other configuration
parameters consistent with its home link properties.
7.3. IPv6 Host Protocol Parameters
This specification does not require any changes to the mobile node's
IP stack. It assumes the mobile node to be a normal IPv4/IPv6 node,
with its protocol operation consistent with the respective
specifications.
However, this specification recommends that the following IPv6
operating parameters on the mobile node be adjusted to the below
recommended values for protocol efficiency and for achieving faster
hand-offs.
Lower Default-Router List Cache Time-out:
As per the base IPv6 specification [RFC-2461], each IPv6 host is
required to maintain certain host data structures including a
Default-Router list. This is the list of on-link routers that have
sent Router Advertisement messages and are eligible to be default
routers on that link. The Router Lifetime field in the received
Router Advertisement defines the life of this entry.
In case of Proxy Mobile IPv6, when a mobile node moves from one link
to another, the source address of the received Router Advertisement
messages advertising the mobile node's home network prefix will be
from a different link-local address and thus making the mobile node
believe that there is a new default-router on the link. It is
important that the mobile node uses the newly learnt default-router
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as supposed to the previously known default-router. The mobile node
must update its default-router list with the new default router entry
and must age out the previously learnt default router entry from its
cache, just as specified in Section 6.3.5 [RFC-2461]. This action is
critical for minimizing packet losses during a hand off switch.
On detecting a reachability problem, the mobile node will certainly
detect the default-router loss by performing the Neighbor
Unreachability Detection procedure, but it is important that the
mobile node times out the previous default router entry at the
earliest. If a given IPv6 host implementation has the provision to
adjust these flush timers, still conforming to the base IPv6 ND
specification, it is desirable to keep the flush-timers to suit the
above consideration.
In access network where SEND [RFC-3971] is not deployed, the mobile
access gateway may withdraw the previous default-router entry, by
sending a Router Advertisement using the link-local address that of
the previous mobile access gateway and with the Router Lifetime field
set to value 0, then this will force the flush of the Previous
Default-Router entry from the mobile node's cache. This certainly
requires context-transfer mechanisms in place for notifying the link-
local address of the default-router on the previous link to the
mobile access gateway on the new link.
There are other solutions possible for this problem, including the
assignment of a unique link-local address for all the mobile access
gateways in a Proxy Mobile IPv6 domain and where SEND [RFC-3971] is
not deployed. In such scenario, the mobile node is not required to
update the default-router entry. However, this is an implementation
choice and has no bearing on the protocol interoperability.
Implementations are free to adopt the best approach that suits their
target deployments.
8. Message Formats
This section defines extensions to the Mobile IPv6 [RFC-3775]
protocol messages.
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8.1. Proxy 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L|K|M|R|P| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: Proxy Binding Update Message
A Binding Update message that is sent by a mobile access gateway to a
local mobility anchor is referred to as the "Proxy Binding Update"
message. A new flag (P) is included in the Binding Update message.
The rest of the Binding Update message format remains the same as
defined in [RFC-3775].
Proxy Registration Flag (P)
A new flag (P) is included in the Binding Update message to indicate
to the local mobility anchor that the Binding Update message is a
proxy registration. The flag MUST be set to the value of 1 for proxy
registrations and MUST be set to 0 for direct registrations sent by a
mobile node.
For descriptions of other fields present in this message, refer to
section 6.1.7 [RFC-3775].
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8.2. Proxy Binding Acknowledgement 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status |K|R|P|Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: Proxy Binding Acknowledgement Message
A Binding Acknowledgement message that is sent by a local mobility
anchor to a mobile access gateway is referred to as the "Proxy
Binding Acknowledgement" message. A new flag (P) is included in the
Binding Acknowledgement message. The rest of the Binding
Acknowledgement message format remains the same as defined in [RFC-
3775].
Proxy Registration Flag (P)
A new flag (P) is included in the Binding Acknowledgement message to
indicate that the local mobility anchor that processed the
corresponding Proxy Binding Update message supports proxy
registrations. The flag is set only if the corresponding Proxy
Binding Update had the Proxy Registration Flag (P) set to value of 1.
For descriptions of other fields present in this message, refer to
the section 6.1.8 [RFC-3775].
8.3. Home Network Prefix Option
A new option, Home Network Prefix Option is defined for using it in
the Proxy Binding Update and Proxy Binding Acknowledgement messages
exchanged between a local mobility anchor and a mobile access
gateway. This option is used for exchanging the mobile node's home
network prefix information.
The Home Network Prefix Option has an alignment requirement of 8n+4.
Its format is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Home Network Prefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
<IANA>
Length
8-bit unsigned integer indicating the length of the option
in octets, excluding the type and length fields. This field
MUST be set to 18.
Reserved
This field is unused for now. The value MUST be initialized
to 0 by the sender and MUST be ignored by the receiver.
Prefix Length
8-bit unsigned integer indicating the prefix length of the
IPv6 prefix contained in the option.
Home Network Prefix
A sixteen-byte field containing the mobile node's IPv6 Home
Network Prefix.
Figure 15: Home Network Prefix Option
8.4. Link-local Address Option
A new option, Link-local Address Option is defined for using it in
the Proxy Binding Update and Proxy Binding Acknowledgement messages
exchanged between a local mobility anchor and a mobile access
gateway. This option is used for exchanging the mobile node's link-
local address.
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The Link-local Address option has an alignment requirement of 8n+6.
Its format is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Link-local Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
<IANA>
Length
8-bit unsigned integer indicating the length of the option
in octets, excluding the type and length fields. This field
MUST be set to 16.
Link-local Address
A sixteen-byte field containing the mobile node's link-local
address.
Figure 16: Link-local Address Option
8.5. Timestamp Option
A new option, Timestamp Option is defined for use in the Proxy
Binding Update and Proxy Binding Acknowledgement messages.
The Timestamp option has an alignment requirement of 8n+2. Its
format is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Timestamp +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
<IANA>
Length
8-bit unsigned integer indicating the length in octets of
the option, excluding the type and length fields. The value
for this field MUST be set to 8.
Timestamp
A 64-bit unsigned integer field containing a timestamp. The value
indicates the number of seconds since January 1, 1970, 00:00 UTC,
by using a fixed point format. In this format, the integer number
of seconds is contained in the first 48 bits of the field, and the
remaining 16 bits indicate the number of 1/64K fractions of a
second.
Figure 17: Timestamp Option
8.6. Status Values
This document defines the following new Status values for use in
Proxy Binding Acknowledgement message. These values are to be
allocated from the same number space, as defined in Section 6.1.8
[RFC-3775].
Status values less than 128 indicate that the Proxy Binding Update
was processed successfully by the local mobility anchor. Status
values greater than 128 indicate that the Proxy Binding Update was
rejected by the local mobility anchor.
PROXY_REG_NOT_ENABLED:
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Proxy Registration not enabled for the mobile node.
MAG_NOT_AUTHORIZED_FOR_PROXY_REG:
The mobile access gateway is not authorized to send proxy binding.
updates.
NOT_AUTHORIZED_FOR_HOME_NETWORK_PREFIX
The mobile node is not authorized for the requesting home network
prefix.
TIMESTAMP_MISMATCH:
Invalid Timestamp value in the received Proxy Binding Update
message.
MISSING_MN_IDENTIFIER_OPTION:
Missing mobile node identifier in the Proxy Binding Update
message.
9. Protocol Configuration Variables
The mobile access gateway MUST allow the following variables to be
configured by the system management.
EnableMAGLocalrouting
This flag indicates whether or not the mobile access gateway is
allowed to enable local routing of the traffic exchanged between a
visiting mobile node and a corresponding node that is locally
connected to one of the interfaces of the mobile access gateway.
The corresponding node can be another visiting mobile node as
well, or a local fixed node.
The default value for this flag is set to "FALSE", indicating that
the mobile access gateway MUST reverse tunnel all the traffic to
the mobile node's local mobility anchor.
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When the value of this flag is set to "TRUE", the mobile access
gateway MUST route the traffic locally.
This aspect of local routing MAY be defined as policy on a per
mobile basis and when present will take precedence over this flag.
The local mobility anchor MUST allow the following variables to be
configured by the system management.
MinDelayBeforeBCEDelete
This variable specifies the amount of time in milliseconds the
local mobility anchor MUST wait before it deletes a Binding Cache
entry of a mobile node, upon receiving a Proxy Binding Update
message from a mobile access gateway with a lifetime value of 0.
During this wait time, if the local mobility anchor receives a
Proxy Binding Update for the same mobile node, identified by its
MN-Identifier, with lifetime value greater than 0, then it must
update the binding cache entry with the accepted binding values.
At the end of this wait-time, if the local mobility anchor did not
receive any valid Proxy Binding Update message, it MUST delete the
Binding Cache entry for that mobile node.
The default value for this variable is 1000 milliseconds.
10. IANA Considerations
This document defines a three new Mobility Header Options, the Home
Network Prefix option, Link-local Address option and the Timestamp
option. These options are described in Sections 8.3, 8.4 and 8.5
respectively. The Type value for these options needs to be assigned
from the same numbering space as allocated for the other mobility
options, as defined in [RFC-3775].
This document also defines new Binding Acknowledgement status values
as described in Section 8.6. The status values MUST be assigned from
the same number space used for Binding Acknowledgement status values,
as defined in [RFC-3775]. The allocated values for each of these
status values MUST be greater than 128.
11. Security Considerations
The potential security threats against any network-based mobility
management protocol are described in [RFC-4832]. This section
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explains how Proxy Mobile IPv6 protocol defends itself against those
threats.
Proxy Mobile IPv6 protocol requires the signaling messages, Proxy
Binding Update and Proxy Binding Acknowledgement, exchanged between
the mobile access gateway and the local mobility anchor to be
protected using IPsec, using the established security association
between them. This essentially eliminates the threats related to the
impersonation of the mobile access gateway or the local mobility
anchor.
This specification allows a mobile access gateway to send binding
registration messages on behalf of a mobile node. If proper
authorization checks are not in place, a malicious node may be able
to hijack a mobile node's session or may do a denial-of-service
attacks. To prevent this attack, this specification requires the
local mobility anchor to allow only authorized mobile access gateways
to send binding registration messages on behalf of a mobile node.
To eliminate the threats on the interface between the mobile access
gateway and the mobile node, this specification requires an
established trust between the mobile access gateway and the mobile
node and to authenticate and authorize the mobile node before it is
allowed to access the network.
To eliminate the threats related to a compromised mobile access
gateway, this specification recommends that the local mobility anchor
before accepting a Proxy Binding Update message for a given mobile
node, should ensure the mobile node is definitively attached to the
mobile access gateway that sent the binding registration request.
The issues related to a compromised mobile access gateway in the
scenario where the local mobility anchor and the mobile access
gateway in different domains, is outside the scope of this document.
This scenario is beyond the applicability of this document.
12. Acknowledgements
The authors would like to specially thank Julien Laganier, Christian
Vogt, Pete McCann, Brian Haley, Ahmad Muhanna, JinHyeock Choi for
their thorough review of this document.
The authors would also like to thank Alex Petrescu, Alice Qinxia,
Alper Yegin, Ashutosh Dutta, Behcet Sarikaya, Fred Templing, Genadi
Velev, George Tsirtsis, Gerardo Giaretta, Henrik Levkowetz, Hesham
Soliman, James Kempf, Jari Arkko, Jean-Michel Combes, John Zhao,
Jong-Hyouk Lee, Jonne Soininen, Jouni Korhonen, Kilian Weniger, Marco
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Liebsch, Mohamed Khalil, Nishida Katsutoshi, Phil Roberts, Ryuji
Wakikawa, Sangjin Jeong, Suresh Krishnan, Vidya Narayanan, Youn-Hee
Han and many others for their passionate discussions in the working
group mailing list on the topic of localized mobility management
solutions. These discussions stimulated much of the thinking and
shaped the draft to the current form. We acknowledge that !
The authors would also like to thank Ole Troan, Akiko Hattori, Parviz
Yegani, Mark Grayson, Michael Hammer, Vojislav Vucetic, Jay Iyer and
Tim Stammers for their input on this document.
13. References
13.1. Normative References
[RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC-2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998.
[RFC-2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[RFC-3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and
M.Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 3315, July 2003.
[RFC-3775] Johnson, D., Perkins, C., Arkko, J., "Mobility Support in
IPv6", RFC 3775, June 2004.
[RFC-4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
Network Access Identifier", RFC 4282, November 2005.
[RFC-4283] Patel, A., Leung, K., Khalil, M., Akhtar, H., and K.
Chowdhury, "Mobile Node Identifier Option for Mobile IPv6", RFC 4283,
November 2005.
[RFC-4301] Kent, S. and Atkinson, R., "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC-4303] Kent, S. "IP Encapsulating Security Protocol (ESP)", RFC
4303, December 2005.
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13.2. Informative References
[RFC-1661] Simpson, W., Ed., "The Point-To-Point Protocol (PPP)", STD
51, RFC 1661, July 1994.
[RFC-2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC-2462] Thompson, S., Narten, T., "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC-2472] Haskin, D. and Allen, E., "IP version 6 over PPP", RFC
2472, December 1998.
[RFC-3041] Narten, T. and Draves, R., "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001.
[RFC-3971] Arkko, J., Ed., Kempf, J., Sommerfeld, B., Zill, B., and
P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March
2005.
[RFC-4306] Kaufman, C, et al, "Internet Key Exchange (IKEv2)
Protocol", RFC 4306, December 2005.
[RFC-4330] Mills, D., "Simple Network Time Protocol (SNTP) Version 4
for IPv4, IPv6 and OSI", RFC 2030, October 1996.
[RFC-4830] Kempf, J., Leung, K., Roberts, P., Nishida, K., Giaretta,
G., Liebsch, M., "Problem Statement for Network-based Localized
Mobility Management", September 2006.
[RFC-4831] Kempf, J., Leung, K., Roberts, P., Nishida, K., Giaretta,
G., Liebsch, M., "Goals for Network-based Localized Mobility
Management", October 2006.
[RFC-4832] Vogt, C., Kempf, J., "Security Threats to Network-Based
Localized Mobility Management", September 2006.
[ID-IPV4-PMIP6] Wakikawa, R. and Gundavelli, S., "IPv4 Support for
Proxy Mobile IPv6", draft-ietf-netlmm-pmip6-ipv4-support-01.txt, May
2007.
[ID-DNAV6] Kempf, J., et al "Detecting Network Attachment in IPv6
Networks (DNAv6)", draft-ietf-dna-protocol-06.txt, October 2006.
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Appendix A. Proxy Mobile IPv6 interactions with AAA Infrastructure
Every mobile node that roams in a proxy Mobile IPv6 domain, would
typically be identified by an identifier, MN-Identifier, and that
identifier will have an associated policy profile that identifies the
mobile node's home network prefix, permitted address configuration
modes, roaming policy and other parameters that are essential for
providing network-based mobility service. This information is
typically configured in AAA. It is possible the home network prefix
is dynamically allocated for the mobile node when it boots up for the
first time in the network, or it could be a statically configured
value on per mobile node basis. However, for all practical purposes,
the network entities in the proxy Mobile IPv6 domain, while serving a
mobile node will have access to this profile and these entities can
query this information using RADIUS/DIAMETER protocols.
Appendix B. Supporting Shared-Prefix Model using DHCPv6
This specification supports Per-MN-Prefix model. However, it is
possible to support Shared-Prefix model under the following
guidelines.
The mobile node is allowed to use stateful address configuration
using DHCPv6 for obtaining its address configuration. The mobile
node is not allowed to use any of the stateless autoconfiguration
techniques. The permitted address configuration models for the
mobile node on the access link can be enforced by the mobile access
gateway, by setting the relevant flags in the Router Advertisements,
as per [RFC-2461].
The Home Network Prefix option that is sent by the mobile access
gateway in the Proxy Binding Update message, must contain the 128-bit
host address that the mobile node obtained via DHCPv6.
Routing state at the mobile access gateway:
For all IPv6 traffic from the source MN-HoA::/128 to
_ANY_DESTINATION_, route via tunnel0, next-hop LMAA, where tunnel0 is
the MAG to LMA tunnel.
Routing state at the local mobility anchor:
For all IPv6 traffic to destination MN-HoA::/128, route via tunnel0,
next-hop Proxy-CoA, where tunnel0 is the LMA to MAG tunnel.
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Authors' Addresses
Sri Gundavelli
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA
Email: sgundave@cisco.com
Kent Leung
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA
Email: kleung@cisco.com
Vijay Devarapalli
Azaire Networks
4800 Great America Pkwy
Santa Clara, CA 95054
USA
Email: vijay.devarapalli@azairenet.com
Kuntal Chowdhury
Starent Networks
30 International Place
Tewksbury, MA
Email: kchowdhury@starentnetworks.com
Basavaraj Patil
Nokia Siemens Networks
6000 Connection Drive
Irving, TX 75039
USA
Email: basavaraj.patil@nsn.com
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