Network Working Group S. Gundavelli, Ed.
Request for Comments: 5213 K. Leung
Category: Standards Track Cisco
V. Devarapalli
Wichorus
K. Chowdhury
Starent Networks
B. Patil
Nokia Siemens Networks
June 2008
Proxy Mobile IPv6
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
Network-based mobility management enables IP mobility for a host
without requiring its participation in any mobility-related
signaling. The network is responsible for managing IP mobility on
behalf of the host. The mobility entities in the network are
responsible for tracking the movements of the host and initiating the
required mobility signaling on its behalf. This specification
describes a network-based mobility management protocol and is
referred to as Proxy Mobile IPv6.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 5
2.1. Conventions Used in This Document . . . . . . . . . . . . 5
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
3. Proxy Mobile IPv6 Protocol Overview . . . . . . . . . . . . . 9
4. Proxy Mobile IPv6 Protocol Security . . . . . . . . . . . . . 15
4.1. Peer Authorization Database (PAD) Example Entries . . . . 16
4.2. Security Policy Database (SPD) Example Entries . . . . . . 17
5. Local Mobility Anchor Operation . . . . . . . . . . . . . . . 17
5.1. Extensions to Binding Cache Entry Data Structure . . . . . 18
5.2. Supported Home Network Prefix Models . . . . . . . . . . . 19
5.3. Signaling Considerations . . . . . . . . . . . . . . . . . 20
5.3.1. Processing Proxy Binding Updates . . . . . . . . . . . 20
5.3.2. Initial Binding Registration (New Mobility Session) . 22
5.3.3. Binding Lifetime Extension (No Handoff) . . . . . . . 23
5.3.4. Binding Lifetime Extension (After Handoff) . . . . . . 23
5.3.5. Binding De-Registration . . . . . . . . . . . . . . . 24
5.3.6. Constructing the Proxy Binding Acknowledgement
Message . . . . . . . . . . . . . . . . . . . . . . . 25
5.4. Multihoming Support . . . . . . . . . . . . . . . . . . . 27
5.4.1. Binding Cache Entry Lookup Considerations . . . . . . 28
5.5. Timestamp Option for Message Ordering . . . . . . . . . . 33
5.6. Routing Considerations . . . . . . . . . . . . . . . . . . 36
5.6.1. Bi-Directional Tunnel Management . . . . . . . . . . . 36
5.6.2. Forwarding Considerations . . . . . . . . . . . . . . 37
5.6.3. Explicit Congestion Notification (ECN)
Considerations for Proxy Mobile IPv6 Tunnels . . . . . 38
5.7. Local Mobility Anchor Address Discovery . . . . . . . . . 39
5.8. Mobile Prefix Discovery Considerations . . . . . . . . . . 39
5.9. Route Optimization Considerations . . . . . . . . . . . . 39 40
6. Mobile Access Gateway Operation . . . . . . . . . . . . . . . 40
6.1. Extensions to Binding Update List Entry Data Structure . . 40 41
6.2. Mobile Node's Policy Profile . . . . . . . . . . . . . . . 41 42
6.3. Supported Access Link Types . . . . . . . . . . . . . . . 42 43
6.4. Supported Address Configuration Modes . . . . . . . . . . 43
6.5. Access Authentication and Mobile Node Identification . . . 43 44
6.6. Acquiring Mobile Node's Identifier . . . . . . . . . . . . 44
6.7. Home Network Emulation . . . . . . . . . . . . . . . . . . 44 45
6.8. Link-Local Link-local and Global Address Uniqueness . . . . . . . . . 45
6.9. Signaling Considerations . . . . . . . . . . . . . . . . . 46 47
6.9.1. Binding Registrations . . . . . . . . . . . . . . . . 46 47
6.9.2. Router Solicitation Messages . . . . . . . . . . . . . 55
6.9.3. Default-Router . . . . . . . . . . . . . . . . . . . . 56
6.9.4. Retransmissions and Rate Limiting . . . . . . . . . . 56 57
6.9.5. Path MTU Discovery . . . . . . . . . . . . . . . . . . 57 58
6.10. Routing Considerations . . . . . . . . . . . . . . . . . . 59
6.10.1. Transport Network . . . . . . . . . . . . . . . . . . 59
6.10.2. Tunneling and Encapsulation Modes . . . . . . . . . . 59
6.10.3. Local Routing . . . . . . . . . . . . . . . . . . . . 60
6.10.4. Tunnel Management . . . . . . . . . . . . . . . . . . 60 61
6.10.5. Forwarding Rules . . . . . . . . . . . . . . . . . . . 61
6.11. Supporting DHCP-Based Address Configuration on the
Access Link . . . . . . . . . . . . . . . . . . . . . . . 62 63
6.12. Home Network Prefix Renumbering . . . . . . . . . . . . . 64 65
6.13. Mobile Node Detachment Detection and Resource Cleanup . . 65
6.14. Allowing Network Access to Other IPv6 Nodes . . . . . . . 65 66
7. Mobile Node Operation . . . . . . . . . . . . . . . . . . . . 66
7.1. Moving into a Proxy Mobile IPv6 Domain . . . . . . . . . . 66
7.2. Roaming in the Proxy Mobile IPv6 Domain . . . . . . . . . 67
8. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 68
8.1. Proxy Binding Update Message . . . . . . . . . . . . . . . 68
8.2. Proxy Binding Acknowledgement Message . . . . . . . . . . 69 70
8.3. Home Network Prefix Option . . . . . . . . . . . . . . . . 71
8.4. Handoff Indicator Option . . . . . . . . . . . . . . . . . 72
8.5. Access Technology Type Option . . . . . . . . . . . . . . 73
8.6. Mobile Node Link-layer Identifier Option . . . . . . . . . 75
8.7. Link-Local Link-local Address Option . . . . . . . . . . . . . . . . 76
8.8. Timestamp Option . . . . . . . . . . . . . . . . . . . . . 76
8.9. Status Values . . . . . . . . . . . . . . . . . . . . . . 77
9. Protocol Configuration Variables . . . . . . . . . . . . . . . 79
9.1. Local Mobility Anchor - Configuration Variables . . . . . 79
9.2. Mobile Access Gateway - Configuration Variables . . . . . 80
9.3. Proxy Mobile IPv6 Domain - Configuration Variables . . . . 81
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 81 82
11. Security Considerations . . . . . . . . . . . . . . . . . . . 82 83
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 83 84
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 84 85
13.1. Normative References . . . . . . . . . . . . . . . . . . . 84 85
13.2. Informative References . . . . . . . . . . . . . . . . . . 85 86
Appendix A. Proxy Mobile IPv6 Interactions with AAA
Infrastructure . . . . . . . . . . . . . . . . . . . 87 88
Appendix B. Routing State . . . . . . . . . . . . . . . . . . . . 87 88
1. Introduction
IP mobility for IPv6 hosts is specified in Mobile IPv6 [RFC3775].
Mobile IPv6 requires client functionality in the IPv6 stack of a
mobile node. Exchange of signaling messages between the mobile node
and home agent enables the creation and maintenance of a binding
between the mobile node's home address and its Care-of Address. care-of address.
Mobility as specified in [RFC3775] requires the IP host to send IP
mobility management signaling messages to the home agent, which is
located in the network.
Network-based mobility is another approach to solving the IP mobility
challenge. It is possible to support mobility for IPv6 nodes without
host involvement by extending Mobile IPv6 [RFC3775] signaling
messages between a network node and a home agent. This approach to
supporting mobility does not require the mobile node to be involved
in the exchange of signaling messages between itself and the home
agent. A proxy mobility agent in the network performs the signaling
with the home agent and does the mobility management on behalf of the
mobile node attached to the network. 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 that are designed to support mobility would be
agnostic to the capability in the IPv6 stack of the nodes that it
serves. IP mobility for nodes that have mobile IP client
functionality in the IPv6 stack as well as those nodes that 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 undergone interoperability testing.
o A common home agent would serve as the mobility agent for all
types of IPv6 nodes.
The problem statement and the need for a network-based mobility
protocol solution has been documented in [RFC4830]. Proxy Mobile
IPv6 is a solution that addresses these issues and requirements.
2. Conventions and 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 [RFC2119].
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
[RFC3775].
This document adopts the terms, Local Mobility Anchor (LMA) and
Mobile Access Gateway (MAG) from the NETLMM Goals document [RFC4831].
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 the 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 set up 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 a
Proxy Mobile IPv6 domain. It is the topological anchor point for
the mobile node's home network prefix(es) and is the entity that
manages the mobile node's binding state. The local mobility
anchor has the functional capabilities of a home agent as defined
in Mobile IPv6 base specification [RFC3775] with the additional
capabilities required for supporting Proxy Mobile IPv6 protocol as
defined in this specification.
Mobile Access Gateway (MAG)
Mobile Access Gateway is a function on an access router 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 to and from the access link and for
signaling the mobile node's local mobility anchor.
Mobile Node (MN)
Throughout this document, the term mobile node is used to refer to
an IP host or router whose mobility is managed by the network.
The mobile node may be an IPv4-only node, IPv6-only node, or a
dual-stack node and is not required to participate in any IP
mobility related signaling for achieving mobility for an IP
address that is obtained in that Proxy Mobile IPv6 domain.
LMA Address (LMAA)
The global 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 which 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 [IPV4-PMIP6].
Proxy Care-of Address (Proxy-CoA)
Proxy-CoA is the global address configured on the egress 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
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 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 [IPV4-PMIP6].
Mobile Node's Home Network Prefix (MN-HNP)
The MN-HNP is a prefix assigned to the link between the mobile
node and the mobile access gateway. More than one prefix can be
assigned to the link between the mobile node and the mobile access
gateway, in which case, all of the assigned prefixes are managed
as a set associated with a mobility session. The mobile node
configures its interface with one or more addresses from its home
network prefix(es). If the mobile node connects to the Proxy
Mobile IPv6 domain through multiple interfaces, simultaneously,
each of the attached interfaces will be assigned a unique set of
home network prefixes, and all the prefixes assigned to a given
interface of a mobile node will be managed under one mobility
session. For example, home network prefixes P1 and P2 assigned to
interface I1 will be managed under one mobility session and
prefixes P3, P4, and P5 assigned to interface I2 of the mobile
node will be managed under a different mobility session.
Additionally, in some configurations the assigned prefix can be of
128-bit prefix length.
Mobile Node's Home Address (MN-HoA)
MN-HoA is an address from a mobile node's home network prefix.
The mobile node will be able to use this address as long as it is
attached to the access network that is in the scope of that Proxy
Mobile IPv6 domain. If the mobile node uses more than one address
from its home network prefix(es), any one of these addresses is
referred to as mobile node's home address. Unlike in Mobile IPv6
where the home agent is aware of the home address of the mobile
node, in Proxy Mobile IPv6, the mobility entities are only aware
of the mobile node's home network prefix(es) and are not always
aware of the exact address(es) that the mobile node configured on
its interface from its home network prefix(es). However, in some
configurations and based on the enabled address configuration
modes on the access link, the mobility entities in the network can
be certain about the exact address(es) configured by the mobile
node.
Mobile Node's Home Link
This is the link on which the mobile node obtained its layer-3
address configuration for the attached interface 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.
Multihomed Mobile Node
A mobile node that connects to the same Proxy Mobile IPv6 domain
through more than one interface and uses these interfaces
simultaneously is referred to as a multihomed mobile node.
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 use
for predictably identifying a mobile node. This is typically an
identifier such as a Network Access Identifier (NAI) [RFC4282] or
other identifier such as a Media Access Control (MAC) address.
Mobile Node Link-layer Identifier (MN-LL-Identifier)
An identifier that identifies the attached interface of a mobile
node. For those interfaces that have a link-layer identifier,
this identifier can be based on that. The link-layer identifier,
in some cases, is generated by the mobile node and conveyed to the
mobile access gateway. This identifier of the attached interface
must be stable, as seen by any of the mobile access gateways in a
given Proxy Mobile IPv6 domain. In some other cases, there might
not be any link-layer identifier associated with the mobile node's
interface. An identifier value of ALL_ZERO is not considered a
valid identifier and cannot be used as an interface identifier.
Policy Profile
Policy Profile is an abstract term for referring to a set of
configuration parameters that are configured for a given mobile
node. The mobility entities in the Proxy Mobile IPv6 domain
require access to these parameters for providing the mobility
management to a given mobile node. The specific details on how
the network entities obtain this policy profile is outside the
scope of this document.
Proxy Binding Update (PBU)
A 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 home network prefix(es) assigned to a given
interface of a mobile node and its current Care-of Address care-of address (Proxy-
CoA).
Proxy Binding Acknowledgement (PBA)
A reply message sent by a local mobility anchor in response to a
Proxy Binding Update message that it received from a mobile access
gateway.
Per-MN-Prefix and Shared-Prefix Models
The term Per-MN-Prefix model is used to refer to an addressing
model where there is a unique network prefix or prefixes assigned
for each node. The term Shared-Prefix model is used to refer to
an addressing model where the prefix(es) are shared by more than
one node. This specification supports the Per-MN-Prefix model and
does not support the Shared-Prefix model.
Mobility Session
In the context of Proxy Mobile IPv6 specification, the term
mobility session refers to the creation or existence of state
associated with the mobile node's mobility binding on the local
mobility anchor and on the serving mobile access gateway.
DHCP
Throughout this document, the acronym DHCP refers to DHCP for
IPv6, as defined in [RFC3315].
ALL_ZERO and NON_ZERO
Protocol message fields initialized with value 0 in each byte of
the field. For example, an 8-byte link-layer identifier field
with the value set to 0 in each of the 8 bytes, or an IPv6 address
with the value 0 in all of the 16 bytes. Conversely, the term
NON_ZERO is used to refer to any value other than an ALL_ZERO
value.
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
[RFC3775].
Proxy Mobile IPv6 protocol is intended for providing network-based IP
mobility management support to a mobile node, without requiring the
participation of the mobile node in any IP mobility related
signaling. The mobility entities in the network will track the
mobile node's movements and will initiate the mobility signaling and
set up the required routing state.
The core functional entities in the NETLMM infrastructure are the
Local Mobility Anchor (LMA) and the Mobile Access Gateway (MAG). The
local mobility anchor is responsible for maintaining the mobile
node's reachability state and is the topological anchor point for the
mobile node's home network prefix(es). 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 to and from the access link and for
initiating binding registrations to the mobile node's local mobility
anchor. There can be multiple local mobility anchors in a Proxy
Mobile IPv6 domain each serving a different group of mobile nodes.
The architecture of a Proxy Mobile IPv6 domain is shown in Figure 1.
+----+ +----+
|LMA1| |LMA2|
+----+ +----+
LMAA1 -> | | <-- LMAA2
| |
\\ //\\
\\ // \\
\\ // \\
+---\\------------- //------\\----+
( \\ IPv4/IPv6 // \\ )
( \\ Network // \\ )
+------\\--------//------------\\-+
\\ // \\
\\ // \\
\\ // \\
Proxy-CoA1--> | | <-- Proxy-CoA2
+----+ +----+
|MAG1|-----{MN2} |MAG2|
+----+ | +----+
| | |
MN-HNP1 --> | MN-HNP2 | <-- MN-HNP3, MN-HNP4
{MN1} {MN3}
Figure 1: Proxy Mobile IPv6 Domain
Once a mobile node enters a Proxy Mobile IPv6 domain and attaches to
an access link, the mobile access gateway on that access link, after
identifying the mobile node and acquiring its identity, will
determine if the mobile node is authorized for the 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 the
address configuration on the connected interface and move anywhere in
that Proxy Mobile IPv6 domain. The obtained address configuration
includes the address(es) from its home network prefix(es), the
default-router address on the link, and other related configuration
parameters. From the perspective of each mobile node, the entire
Proxy Mobile IPv6 domain appears as a single link, the network
ensures that the mobile node does not detect any change with respect
to its layer-3 attachment even after changing its point of attachment
in the network.
The mobile node may be an IPv4-only node, IPv6-only node, or a dual
IPv4/IPv6 node. 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 address and move anywhere in that Proxy Mobile IPv6
domain. However, this specification only supports IPv6 address
mobility and when the transport network is an IPv6 network. The
support for IPv4 addressing or an IPv4 transport network is specified
in the companion document [IPV4-PMIP6].
If the mobile node connects to the Proxy Mobile IPv6 domain through
multiple interfaces and over multiple access networks, the network
will allocate a unique set of home network prefixes for each of the
connected interfaces. The mobile node will be able to configure
address(es) on those interfaces from the respective home network
prefix(es). However, if the mobile node performs a handoff by moving
its address configuration from one interface to the other, and if the
local mobility anchor receives a handoff hint from the serving mobile
access gateway about the same, the local mobility anchor will assign
the same home network prefix(es) that it previously assigned prior to
the handoff. The mobile node will also be able to perform a handoff
by changing its point of attachment from one mobile access gateway to
a different mobile access gateway using the same interface and will
be able to retain the address configuration on the attached
interface.
+-----+ +-----+ +-----+
| MN | | MAG | | LMA |
+-----+ +-----+ +-----+
| | |
MN Attached | |
| | |
| MN Attached Event from MN/Network |
| (Acquire MN-Id and Profile) |
| | |
|--- Rtr Sol --------->| |
| | |
| |--- PBU ------------->|
| | |
| | Accept PBU
| | (Allocate MN-HNP(s), Setup BCE and Tunnel)
| | |
| |<------------- PBA ---|
| | |
| Accept PBA |
| (Setup (Set Up Tunnel and Routing) |
| | |
| |==== Bi-Dir Tunnel ===|
| | |
|<--------- 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. The Router Solicitation message from
the mobile node may arrive at any time after the mobile node's
attachment and has no strict ordering relation with the other
messages in the call flow.
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(es). It also creates the Binding
Cache entry and sets up its endpoint of the bi-directional tunnel to
the mobile access gateway.
The mobile access gateway on receiving the Proxy Binding
Acknowledgement message sets up its endpoint of the bi-directional
tunnel to the local mobility anchor and also sets up the forwarding
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(es) as the hosted on-link prefix(es).
The mobile node, on receiving these Router Advertisement messages on
the access link, will attempt to configure its interface using either
stateful or stateless address configuration modes, based on the modes
that are permitted on that access link as indicated in Router
Advertisement messages. At the end of a successful address
configuration procedure, the mobile node will end up with one or more
addresses from its home network prefix(es).
Once the address configuration is complete, the mobile node has one
or more valid addresses from its home network prefix(es) 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 any one
or more of the addresses from its home network prefix(es).
The local mobility anchor, being the topological anchor point for the
mobile node's home network prefix(es), receives any packets that are
sent to the mobile node by any node in or outside the Proxy Mobile
IPv6 domain. The 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. However, in some
cases, the traffic sent from a correspondent node that is locally
connected to the mobile access gateway may not be received by the
local mobility anchor and may be routed locally by the mobile access
gateway (refer to Section 6.10.3).
The mobile access gateway acts as the default router on the point-to-
point link shared with the mobile node. Any packet that the mobile
node sends to any correspondent 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. However, in some
cases, the traffic sent to a correspondent node that is locally
connected to the mobile access gateway may be locally routed by the
mobile access gateway (refer to Section 6.10.3).
+-----+ +-----+ +-----+ +-----+
| MN | |p-MAG| | LMA | |n-MAG|
+-----+ +-----+ +-----+ +-----+
| | | |
| |==Bi-Dir Tunnel=| |
MN Detached | | |
| MN Detached Event | |
| | | |
| |-- DeReg PBU -->| |
| | | |
| | Accept PBU |
| | (Start MinDelayBeforeBCEDelete Timer)
| | | |
| |<-------- PBA --| |
| | | |
MN Attached | | |
| | | MN Attached event received
| | | from MN or from network
| | | (Acquire MN-Id and Profile)
| | | |
|--- Rtr Sol ------------------------------------->|
....
Registration steps as in Fig. 2.
....
| | |==Bi-Dir Tunnel=|
| | | |
|<------------------------------------ Rtr Adv ----|
| | | |
MN retains HoA/HNP(s)
| | | |
Figure 3: Mobile Node Handoff - Signaling Call Flow
Figure 3 shows the signaling call flow for the mobile node's handoff
from the previously attached mobile access gateway (p-MAG) to the
newly attached mobile access gateway (n-MAG). This call flow only
reflects a specific message ordering, it is possible the registration
message from the n-MAG may arrive before the de-registration message
from the p-MAG arrives.
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 previous link will detect the mobile
node's detachment from the link. It will signal the local mobility
anchor and will remove the binding and routing state for that mobile
node. The local mobility anchor, upon receiving this request, will
identify the corresponding mobility session for which the request was
received, and once it accepts the request, will wait for a certain
amount of time to allow the mobile access gateway on the new link to
update the binding. However, if it does not receive any Proxy
Binding Update message within the given amount of time, it will
delete the binding cache entry.
The mobile access gateway on the new access link, upon detecting the
mobile node on its access link, will signal the local mobility anchor
to update the binding state. Once that signaling is complete, the
serving mobile access gateway will send the Router Advertisements
containing the mobile node's home network prefix(es), and this will
ensure the mobile node will not detect any change with respect to the
layer-3 attachment of its interface.
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.
The mobile access gateway and the local mobility anchor MUST
implement IPsec for protecting the Proxy Mobile IPv6 signaling
messages [RFC4301]. That is, IPsec is a mandatory-to-implement
security mechanism. However, additional documents may specify
alternative mechanisms and the mobility entities can enable a
specific mechanism for securing Proxy Mobile IPv6 signaling messages,
based on either a static configuration or after a dynamic negotiation
using any standard security negotiation protocols. As in Mobile IPv6
[RFC3775], the use of IPsec for protecting a mobile node's data
traffic is optional.
IPsec Encapsulating Security Payload (ESP) [RFC4303] in transport
mode with mandatory integrity protection SHOULD be used for
protecting the signaling messages. Confidentiality protection of
these messages is not required.
IPsec ESP [RFC4303] in tunnel mode MAY be used to protect the mobile
node's tunneled data traffic, if protection of data traffic is
required.
Internet Key Exchange Protocol version 2 (IKEv2) [RFC4306] SHOULD be
used to set up 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 [RFC4306], for mutual
authentication.
The Mobile IPv6 specification [RFC3775] 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, the local mobility
anchor MUST restrict the creation and manipulation of proxy bindings
to specifically authorized mobile access gateways and prefixes. The
local mobility anchor MUST be locally configurable to authorize such
specific combinations. Additional mechanisms, such as a policy store
or Authentication, Authorization, and Accounting (AAA) may be
employed, but these are outside the scope of this specification.
Unlike in Mobile IPv6 [RFC3775], these signaling messages do not
carry either the Home Address destination option or the Type 2
Routing header, and hence the policy entries and security association
selectors stay the same and require no special IPsec related
considerations.
4.1. Peer Authorization Database (PAD) Example Entries
This section describes PAD entries [RFC4301] 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
implementation can implement the PAD in any implementation-specific
manner. The PAD state may also be distributed across various
databases in a specific implementation.
In the example shown below, the identity of the local mobility anchor
is assumed to be lma_identity_1 and the identity of the mobile access
gateway is assumed to be mag_identity_1.
mobile access gateway PAD:
- IF remote_identity = lma_identity_1
Then authenticate (shared secret/certificate/EAP)
and authorize CHILD_SAs for remote address lma_address_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
Figure 4: PAD Entries
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 (SPD) Example Entries
This section describes the security policy entries [RFC4301] 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 example shown below, the identity of the mobile access gateway
is assumed to be mag_identity_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. The acronym MH
represents the protocol number for the Mobility Header [RFC3775],
while the terms local_mh_type and remote_mh_type stand for local
mobility header type and remote mobility header type, respectively.
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_identity_1 to address lma_address_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
Figure 5: SPD Entries
5. Local Mobility Anchor Operation
The local mobility anchor MUST support the home agent function as
defined in [RFC3775] and the extensions defined in this
specification. A home agent with these modifications and enhanced
capabilities for supporting the Proxy Mobile IPv6 protocol is
referred to as a local mobility anchor.
This 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. A Binding Cache entry is a
conceptual data structure, described in Section 9.1 of [RFC3775].
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 set to value 1
for Binding Cache entries that are proxy registrations and is set
to value 0 for all other entries.
o The identifier of the registered mobile node, MN-Identifier. This
identifier is obtained from the Mobile Node Identifier Option
[RFC4283] present in the received Proxy Binding Update message.
o The link-layer identifier of the mobile node's connected interface
on the access link. This identifier can be acquired from the
Mobile Node Link-layer Identifier option, present in the received
Proxy Binding Update message. If the option was not present in
the request, this variable length field MUST be set to two
(octets) and MUST be initialized to a value of ALL_ZERO.
o The link-local address of the mobile access gateway on the point-
to-point link shared with the mobile node. This is generated by
the local mobility anchor after accepting the initial Proxy
Binding Update message.
o A list of IPv6 home network prefixes assigned to the mobile node's
connected interface. The home network prefix(es) may have been
statically configured in the mobile node's policy profile, or,
they may have been dynamically allocated by the local mobility
anchor. Each one of these prefix entries will also include the
corresponding prefix length.
o The tunnel interface identifier (tunnel-if-id) of the bi-
directional tunnel between the local mobility anchor and the
mobile access gateway where the mobile node is currently anchored.
This is internal to the local mobility anchor. The tunnel
interface identifier is acquired during the tunnel creation.
o The access technology type, by which the mobile node is currently
attached. This is obtained from the Access Technology Type
option, present in the Proxy Binding Update message.
o The 64-bit timestamp value of the most recently accepted Proxy
Binding Update message sent for this mobile node. This is the
time of day on the local mobility anchor, when the message was
received. If the Timestamp option is not present in the Proxy
Binding Update message (i.e., when the sequence-number-based
scheme is in use), the value MUST be set to ALL_ZERO.
Typically, any one of the mobile node's home network prefixes from
its mobility session may be used as a key for locating its Binding
Cache entry in all cases except when there has been a handoff of the
mobile node's session to a new mobile access gateway, and that mobile
access gateway is unaware of the home network prefix(es) assigned to
that mobility session. In such handoff cases, the Binding Cache
entry can be located under the considerations specified in Section
5.4.1.
5.2. Supported Home Network Prefix Models
This specification supports the Per-MN-Prefix model and does not
support the Shared-Prefix model. According to the Per-MN-Prefix
model, home network prefix(es) assigned to a mobile node are for that
mobile node's exclusive use and no other node shares an address from
that prefix (other than the Subnet-Router anycast address [RFC4291]
that is used by the mobile access gateway hosting that prefix on that
link).
There may be more than one prefix assigned to a given interface of
the mobile node; all of those assigned prefixes MUST be unique to
that mobile node, and all are part of exactly one mobility session.
If the mobile node simultaneously attaches to the Proxy Mobile IPv6
domain through multiple interfaces, each of the attached interfaces
MUST be assigned one or more unique prefixes. Prefixes that are not
assigned to the same interface MUST NOT be managed under the same
mobility session.
The mobile node's home network prefix(es) assigned to a given
interface of a mobile node (part of a mobility session) will be
hosted on the access link where the mobile node is attached (using
that interface). The local mobility anchor is not required to
perform any proxy Neighbor Discovery (ND) operations [RFC4861] for
defending the mobile node's home address(es), as the prefixes are not
locally hosted on the local mobility anchor. However, from the
routing perspective, the home network prefix(es) is topologically
anchored on the local mobility anchor.
5.3. Signaling Considerations
This section provides the rules for processing the signaling
messages. The processing rules specified in this section and other
related sections are chained and are in a specific order. When
applying these considerations for processing the signaling messages,
the specified order MUST be maintained.
5.3.1. Processing Proxy Binding Updates
1. The received Proxy Binding Update message (a Binding Update
message with the 'P' flag set to value of 1, format specified in
Section 8.1) MUST be authenticated as described in Section 4.
When IPsec is used for message authentication, the Security
Parameter Index (SPI) in the IPsec header [RFC4306] of the
received packet is needed for locating the security association,
for authenticating the Proxy Binding Update message.
2. The local mobility anchor MUST observe the rules described in
Section 9.2 of [RFC3775] when processing the Mobility Header in
the received Proxy Binding Update message.
3. The local mobility anchor MUST ignore the check, specified in
Section 10.3.1 of [RFC3775], related to the presence of the Home
Address destination option in the Proxy Binding Update message.
4. The local mobility anchor MUST identify the mobile node from the
identifier present in the Mobile Node Identifier option
[RFC4283] of the Proxy Binding Update message. If the Mobile
Node Identifier option is not present in the Proxy Binding
Update message, 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 option) and the identifier in the Mobile Node
Identifier option carried in the message MUST be set to a zero
length identifier.
5. The local mobility anchor MUST apply the required policy checks,
as explained in Section 4, to verify that the sender is a
trusted mobile access gateway authorized to send Proxy Binding
Update messages on behalf of this mobile node.
6. If the local mobility anchor determines that the requesting node
is not authorized to send Proxy Binding Update messages for the
identified mobile node, it MUST reject the request and send a
Proxy Binding Acknowledgement message with the Status field set
to MAG_NOT_AUTHORIZED_FOR_PROXY_REG (not authorized to send
proxy binding updates).
7. If the local mobility anchor cannot identify the mobile node
based on the identifier present in the Mobile Node Identifier
option [RFC4283] of the Proxy Binding Update message, it MUST
reject the request and send a Proxy Binding Acknowledgement
message with the Status field set to
NOT_LMA_FOR_THIS_MOBILE_NODE (Not a local mobility anchor for
this mobile node).
8. If the local mobility anchor determines that the mobile node is
not authorized for the network-based mobility management
service, it MUST reject the request and send a Proxy Binding
Acknowledgement message with the Status field set to
PROXY_REG_NOT_ENABLED (Proxy Registration not enabled).
9. The local mobility anchor MUST apply the considerations
specified in Section 5.5 for processing the Sequence Number
field and the Timestamp option (if present) in the Proxy Binding
Update message.
10. If there is no Home Network Prefix option(s) (with any value)
present in the Proxy Binding Update message, the local mobility
anchor MUST reject the request and send a Proxy Binding
Acknowledgement message with the Status field set to
MISSING_HOME_NETWORK_PREFIX_OPTION (Missing Home Network Prefix
option).
11. If the Handoff Indicator option is not present in the Proxy
Binding Update message, the local mobility anchor MUST reject
the request and send a Proxy Binding Acknowledgement message
with the Status field set to MISSING_HANDOFF_INDICATOR_OPTION
(Missing Handoff Indicator option).
12. If the Access Technology Type option is not present in the Proxy
Binding Update message, the local mobility anchor MUST reject
the request and send a Proxy Binding Acknowledgement message
with the Status field set to MISSING_ACCESS_TECH_TYPE_OPTION
(Missing Access Technology Type option).
13. Considerations specified in Section 5.4.1 MUST be applied for
performing the Binding Cache entry existence test. If those
checks specified in Section 5.4.1 result in associating the
received Proxy Binding Update message to a new mobility session
creation request, considerations from Section 5.3.2 (Initial
Binding Registration - New Mobility Session), MUST be applied.
If those checks result in associating the request to an existing
mobility session, the following checks determine the next set of
processing rules that need to be applied.
* If the Handoff Indicator field in the Handoff Indicator
option present in the request is set to a value of 5 (Handoff
state not changed), considerations from Section 5.3.3
(Binding Lifetime Extension - No handoff) MUST be applied.
* If the received Proxy Binding Update message has the lifetime
value of zero, considerations from Section 5.3.5 (Binding De-
Registration) MUST be applied.
* For all other cases, considerations from Section 5.3.4
(Binding Lifetime Extension - After handoff) MUST be applied.
14. When sending the Proxy Binding Acknowledgement message with any
Status field value, the message MUST be constructed as specified
in Section 5.3.6.
5.3.2. Initial Binding Registration (New Mobility Session)
1. If there is at least one instance of the Home Network Prefix
option present in the Proxy Binding Update message with the
prefix value set to ALL_ZERO, the local mobility anchor MUST
allocate one or more home network prefixes to the mobile node and
assign it to the new mobility session created for the mobile
node. The local mobility anchor MUST ensure the allocated
prefix(es) is not in use by any other node or mobility session.
The decision on how many prefixes to be allocated for the
attached interface can be based on a global policy or a policy
specific to that mobile node. However, when stateful address
autoconfiguration using DHCP is supported on the link,
considerations from Section 6.11 MUST be applied for the prefix
assignment.
2. If the local mobility anchor is unable to allocate any home
network prefix for the mobile node, it MUST reject the request
and send a Proxy Binding Acknowledgement message with the Status
field set to 130 (Insufficient resources).
3. If there are one or more Home Network Prefix options present in
the Proxy Binding Update message (with each of the prefixes set
to a NON_ZERO value), the local mobility anchor, before accepting
that request, MUST ensure each one of those prefixes is owned by
the local mobility anchor, and further that the mobile node is
authorized to use these prefixes. If the mobile node is not
authorized to use any one or more of those prefixes, the local
mobility anchor MUST reject the request and send a Proxy Binding
Acknowledgement message with the Status field set to
NOT_AUTHORIZED_FOR_HOME_NETWORK_PREFIX (mobile node not
authorized for one or more of the requesting home network
prefixes).
4. 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
registration.
5. If there is no existing bi-directional tunnel to the mobile
access gateway that sent the request, the local mobility anchor
MUST establish a bi-directional tunnel to that mobile access
gateway. Considerations from Section 5.6.1 MUST be applied for
managing the dynamically created bi-directional tunnel.
6. The local mobility anchor MUST create a prefix route(s) over the
tunnel to the mobile access gateway for forwarding any traffic
received for the mobile node's home network prefix(es) associated
with this mobility session. The created tunnel and the routing
state MUST result in the forwarding behavior on the local
mobility anchor as specified in Section 5.6.2.
7. The local mobility anchor MUST send the Proxy Binding
Acknowledgement message with the Status field set to 0 (Proxy
Binding Update Accepted). The message MUST be constructed as
specified in Section 5.3.6.
5.3.3. Binding Lifetime Extension (No Handoff)
1. Upon accepting the Proxy Binding Update message for extending the
binding lifetime, received from the same mobile access gateway
(if the Proxy-CoA address in the Binding Cache entry is the same as the
Proxy-CoA address in the request) that last updated the binding, the
local mobility anchor MUST update the Binding Cache entry with
the accepted registration values.
2. The local mobility anchor MUST send the Proxy Binding
Acknowledgement message with the Status field set to 0 (Proxy
Binding Update Accepted). The message MUST be constructed as
specified in Section 5.3.6.
5.3.4. Binding Lifetime Extension (After Handoff)
1. Upon accepting the Proxy Binding Update message for extending the
binding lifetime, received from a new mobile access gateway (if
the Proxy-CoA address in the Binding Cache entry does not match the
Proxy-CoA address in the request) where the mobile node's mobility
session is handed off, the local mobility anchor MUST update the
Binding Cache entry with the accepted registration values.
2. The local mobility anchor MUST remove the previously created
route(s) for the mobile node's home network prefix(es) associated
with this mobility session. Additionally, if there are no other
mobile nodes sharing the dynamically created bi-directional
tunnel to the previous mobile access gateway, the tunnel SHOULD
be deleted, applying considerations from section 5.6.1 (if the
tunnel is a dynamically created tunnel and not a fixed pre-
established tunnel).
3. If there is no existing bi-directional tunnel to the mobile
access gateway that sent the request, the local mobility anchor
MUST establish a bi-directional tunnel to that mobile access
gateway. Considerations from Section 5.6.1 MUST be applied for
managing the dynamically created bi-directional tunnel.
4. The local mobility anchor MUST create prefix route(s) over the
tunnel to the mobile access gateway for forwarding any traffic
received for the mobile node's home network prefix(es) associated
with that mobility session. The created tunnel and routing state
MUST result in the forwarding behavior on the local mobility
anchor as specified in Section 5.6.2.
5. The local mobility anchor MUST send the Proxy Binding
Acknowledgement message with the Status field set to 0 (Proxy
Binding Update Accepted). The message MUST be constructed as
specified in Section 5.3.6.
5.3.5. Binding De-Registration
1. If the received Proxy Binding Update message with the lifetime
value of zero, has a Source Address in the IPv6 header (or the
address in the Alternate Care-of Address option, if the option is
present) different from what is present in the Proxy-CoA address field in
the Binding Cache entry, the local mobility anchor MUST ignore
the request.
2. Upon accepting the Proxy Binding Update message, with the
lifetime value of zero, the local mobility anchor MUST wait for
MinDelayBeforeBCEDelete amount of time, before it deletes the
Binding Cache entry. However, it MUST send the Proxy Binding
Acknowledgement message with the Status field set to 0 (Proxy
Binding Update Accepted). The message MUST be constructed as
specified in Section 5.3.6.
* During this wait period, the local mobility anchor SHOULD drop
the mobile node's data traffic.
* During this wait period, if the local mobility anchor receives
a valid Proxy Binding Update message for the same mobility
session 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 newly accepted
registration values, and the wait period should be ended.
* By the end of this wait period, if the local mobility anchor
did not receive any valid Proxy Binding Update messages for
this mobility session, then it MUST delete the Binding Cache
entry and remove the routing state created for that mobility
session. The local mobility anchor can potentially reassign
the prefix(es) associated with this mobility session to other
mobile nodes.
5.3.6. 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.
IPv6 header (src=LMAA, dst=Proxy-CoA)
Mobility header
- BA /* P flag must be set to value of 1 */
Mobility Options
- Mobile Node Identifier option (mandatory)
- Home Network Prefix option(s) (mandatory)
- Handoff Indicator option (mandatory)
- Access Technology Type option (mandatory)
- Timestamp option (optional)
- Mobile Node Link-layer Identifier option (optional)
- Link-local Address option (optional)
Figure 6: Proxy Binding Acknowledgement Message Format
o The Source Address field in the IPv6 header of the message MUST be
set to the destination address of the received Proxy Binding
Update message.
o The Destination Address field in the IPv6 header of the message
MUST be set to the source address of the received Proxy Binding
Update message. When there is no Alternate Care-of Address option
present in the request, the destination address is the same as the
Proxy-CoA address,
Proxy-CoA; otherwise, the address may not be the same as the
Proxy-CoA.
o The Mobile Node Identifier option [RFC4283] MUST be present. The
identifier field in the option MUST be copied from the Mobile Node
Identifier option in the received Proxy Binding Update message.
If the option was not present in the request, the identifier in
the option MUST be set to a zero length identifier.
o At least one Home Network Prefix option MUST be present.
* If the Status field is set to a value greater than or equal to
128, i.e., if the Proxy Binding Update is rejected, all the
Home Network Prefix options that were present in the request
(along with their prefix values) MUST be present in the reply.
But, if there was no Home Network Prefix option present in the
request, then there MUST be only one Home Network Prefix option
with the value in the option set to ALL_ZERO.
* For all other cases, there MUST be a Home Network Prefix option
for each of the assigned home network prefixes (for that
mobility session), and with the prefix value in the option set
to the allocated prefix value.
o The Handoff Indicator option MUST be present. The handoff
indicator field in the option MUST be copied from the Handoff
Indicator option in the received Proxy Binding Update message. If
the option was not present in the request, the value in the option
MUST be set to zero.
o The Access Technology Type option MUST be present. The access
technology type field in the option MUST be copied from the Access
Technology Type option in the received Proxy Binding Update
message. If the option was not present in the request, the value
in the option MUST be set to zero.
o The Timestamp option MUST be present only if the same option was
present in the received Proxy Binding Update message and MUST NOT
be present otherwise. Considerations from Section 5.5 must be
applied for constructing the Timestamp option.
o The Mobile Node Link-layer Identifier option MUST be present only
if the same option was present in the received Proxy Binding
Update message and MUST NOT be present otherwise. The link-layer
identifier value MUST be copied from the Mobile Node Link-layer
Identifier option present in the received Proxy Binding Update
message.
o The Link-local Address option MUST be present only if the same
option was present in the received Proxy Binding Update message
and MUST NOT be present otherwise. If the Status field in the
reply is set to a value greater than or equal to 128, i.e., if the
Proxy Binding Update is rejected, then the link-local address from
the request MUST be copied to the Link-local Address option in the
reply, otherwise the following considerations apply.
* If the received Proxy Binding Update message has the Link-local
Address option with ALL_ZERO value and if there is an existing
Binding Cache entry associated with this request, then the
link-local address from the Binding Cache entry MUST be copied
to the Link-local Address option in the reply.
* If the received Proxy Binding Update message has the Link-local
Address option with ALL_ZERO value and if there is no existing
Binding Cache entry associated with this request, then the
local mobility anchor MUST generate the link-local address that
the mobile access gateway can use on the point-to-point link
shared with the mobile node. This generated address MUST be
copied to the Link-local Address option in the reply. The same
address MUST also be copied to the link-local address field of
Binding Cache entry created for this mobility session.
* If the received Proxy Binding Update message has the Link-local
Address option with NON_ZERO value, then the link-local address
from the request MUST be copied to the Link-local Address
option in the reply. The same address MUST also be copied to
the link-local address field of the Binding Cache entry
associated with this request (after creating the Binding Cache
entry, if one does not exist).
o If IPsec is used for protecting the signaling messages, the
message MUST be protected using the security association existing
between the local mobility anchor and the mobile access gateway.
o Unlike in Mobile IPv6 [RFC3775], the Type 2 Routing header MUST
NOT be present in the IPv6 header of the packet.
5.4. Multihoming Support
This specification allows mobile nodes to connect to a Proxy Mobile
IPv6 domain through multiple interfaces for simultaneous access. The
following are the key aspects of this multihoming support.
o When a mobile node connects to a Proxy Mobile IPv6 domain through
multiple interfaces for simultaneous access, the local mobility
anchor MUST allocate a mobility session for each of the attached
interfaces. Each mobility session should be managed under a
separate Binding Cache entry and with its own lifetime.
o The local mobility anchor MAY allocate more than one home network
prefix for a given interface of the mobile node. However, all the
prefixes associated with a given interface MUST be managed as part
of one mobility session, associated with that interface.
o The local mobility anchor MUST allow for a handoff between two
different interfaces of a mobile node. In such a scenario, all
the home network prefixes associated with one interface (part of
one mobility session) will be associated with a different
interface of the mobile node. The decision on when to create a
new mobility session and when to update an existing mobility
session MUST be based on the Handover hint present in the Proxy
Binding Update message and under the considerations specified in
this section.
5.4.1. Binding Cache Entry Lookup Considerations
There can be multiple Binding Cache entries for a given mobile node.
When doing a lookup for a mobile node's Binding Cache entry for
processing a received Proxy Binding Update message, the local
mobility anchor MUST apply the following multihoming considerations
(in the below specified order, starting with Section 5.4.1.1). These
rules are chained with the processing rules specified in Section 5.3.
5.4.1.1. Home Network Prefix Option (NON_ZERO Value) Present in the
Request
+=====================================================================+
| Registration/De-Registration Message |
+=====================================================================+
| At least one HNP Option with NON_ZERO Value |
+=====================================================================+
| ATT |
+=====================================================================+
| MN-LL-Identifier Opt Present | MN-LL-Identifier Opt Not Present |
+=====================================================================+
| HI |
+==================================+==================================+
| BCE Lookup Key: Any of the Home Network Prefixes from the request |
+=====================================================================+
Figure 7: Binding Cache Entry (BCE) Lookup Using Home Network Prefix
If there is at least one Home Network Prefix option present in the
request with a NON_ZERO prefix value and irrespective of the presence
of the Mobile Node Link-layer Identifier option in the request, the
following considerations MUST be applied. If there is more than one
instance of the Home Network Prefix option, any one of the Home
Network Prefix options present in the request (with NON_ZERO prefix
value) can be used for locating the Binding Cache entry.
1. The local mobility anchor MUST verify if there is an existing
Binding Cache entry with one of its home network prefixes
matching the prefix value in one of the Home Network Prefix
options of the received Proxy Binding Update message.
2. If a Binding Cache entry does not exist (with one of its home
network prefixes in the Binding Cache entry matching the prefix
value in one of the Home Network Prefix options of the received
Proxy Binding Update message), the request MUST be considered as
a request for creating a new mobility session.
3. If there exists a Binding Cache entry (with one of its home
network prefixes in the Binding Cache entry matching the prefix
value in one of the Home Network Prefix options of the received
Proxy Binding Update message), but if the mobile node identifier
in the entry does not match the mobile node identifier in the
Mobile Node Identifier option of the received Proxy Binding
Update message, the local mobility anchor MUST reject the request
with the Status field value set to
NOT_AUTHORIZED_FOR_HOME_NETWORK_PREFIX (mobile node is not
authorized for one or more of the requesting home network
prefixes).
4. If there exists a Binding Cache entry (matching MN-Identifier and
one of its home network prefixes in the Binding Cache entry
matching the prefix value in one of the Home Network Prefix
options of the received Proxy Binding Update message), but if all
the prefixes in the request do not match all the prefixes in the
Binding Cache entry, or if they do not match in count, then the
local mobility anchor MUST reject the request with the Status
field value set to BCE_PBU_PREFIX_SET_DO_NOT_MATCH (all the home
network prefixes listed in the BCE do not match all the prefixes
in the received PBU).
5. If there exists a Binding Cache entry (matching MN-Identifier and
all the home network prefixes in the Binding Cache entry matching
all the home network prefixes in the received Proxy Binding
Update message) and if any one or more of these below stated
conditions match, the request MUST be considered as a request for
updating that Binding Cache entry.
* If the Handoff Indicator field in the Handoff Indicator option
present in the request is set to a value of 2 (Handoff between
two different interfaces of the mobile node).
* If there is no Mobile Node Link-layer Identifier option
present in the request, the link-layer identifier value in the
Binding Cache entry is set to ALL_ZERO, the access technology
type field in the Access Technology Type option present in the
request matches the access technology type in the Binding
Cache entry, and if the Handoff Indicator field in the Handoff
Indicator option present in the request is set to a value of 3
(Handoff between mobile access gateways for the same
interface).
* If the Proxy-CoA address in the Binding Cache entry matches the source
address of the request (or the address in the
alternate Alternate
Care-of Address option, if the option is present) and if the
access technology type field in the Access Technology Type
option present in the request matches the access technology
type in the Binding Cache entry.
6. For all other cases, the message MUST be considered as a request
for creating a new mobility session. However, if the received
Proxy Binding Update message has the lifetime value of zero and
if the request cannot be associated with any existing mobility
session, the message MUST be silently ignored.
5.4.1.2. Mobile Node Link-Layer Link-layer Identifier Option Present in the
Request
+=====================================================================+
| Registration/De-Registration Message |
+=====================================================================+
| No HNP option with a NON_ZERO Value |
+=====================================================================+
| ATT |
+=====================================================================+
| MN-LL-Identifier Option Present (NON_ZERO Value) |
+=====================================================================+
| HI |
+==================================+==================================+
| BCE Lookup Keys: (MN-Identifier + ATT + MN-LL-Identifier) |
+=====================================================================+
Figure 8: BCE Lookup Using Link-Layer Link-layer Identifier
If there is no Home Network Prefix option present in the request with
a NON_ZERO prefix value, but if there is a Mobile Node Link-layer
Identifier option present in the request, then the following
considerations MUST be applied for locating the Binding Cache entry.
1. The local mobility anchor MUST verify if there is an existing
Binding Cache entry, with the mobile node identifier matching the
identifier in the received Mobile Node Identifier option, access
technology type matching the value in the received Access
Technology Type option, and the link-layer identifier value
matching the identifier in the received Mobile Node Link-layer
Identifier option.
2. If there exists a Binding Cache entry (matching MN-Identifier,
Access Technology Type (ATT), and MN-LL-Identifier), the request
MUST be considered as a request for updating that Binding Cache
entry.
3. If there does not exist a Binding Cache entry (matching MN-
Identifier, ATT, and MN-LL-Identifier) and the Handoff Indicator
field in the Handoff Indicator option present in the request is
set to a value of 2 (Handoff between two different interfaces of
the mobile node). The local mobility anchor MUST apply the
following additional considerations.
* The local mobility anchor MUST verify if there exists one and
only one Binding Cache entry with the mobile node identifier
matching the identifier in the Mobile Node Identifier option
present in the request and for any link-layer identifier
value. If there exists only one such entry (matching the MN-
Identifier), the request MUST be considered as a request for
updating that Binding Cache entry.
4. If there does not exist a Binding Cache entry (matching MN-
Identifier, ATT, and MN-LL-Identifier) and if the Handoff
Indicator field in the Handoff Indicator option present in the
request is set to a value of 4 (Handoff state unknown), the local
mobility anchor MUST apply the following additional
considerations.
* The local mobility anchor MUST verify if there exists one and
only one Binding Cache entry with the mobile node identifier
matching the identifier in the Mobile Node Identifier option
present in the request and for any link-layer identifier
value. If there exists only one such entry (matching the MN-
Identifier), the local mobility anchor SHOULD wait until the
existing Binding Cache entry is de-registered by the
previously serving mobile access gateway, before the request
can be considered as a request for updating that Binding Cache
entry. However, if there is no de-registration message that
is received within MaxDelayBeforeNewBCEAssign amount of time,
the local mobility anchor, upon accepting the request, MUST
consider the request as a request for creating a new mobility
session. The local mobility anchor MAY also choose to create
a new mobility session without waiting for a de-registration
message, and this should be configurable on the local mobility
anchor.
5. For all other cases, the message MUST be considered as a request
for creating a new mobility session. However, if the received
Proxy Binding Update message has the lifetime value of zero and
if the request cannot be associated with any existing mobility
session, the message MUST be silently ignored.
5.4.1.3. Mobile Node Link-Layer Link-layer Identifier Option Not Present in the
Request
+=====================================================================+
| Registration/De-Registration Message | +=====================================================================+
| No HNP option with a NON_ZERO Value |
+=====================================================================+
| ATT |
+=====================================================================+
| MN-LL-Identifier Option Not Present |
+=====================================================================+
| HI |
+==================================+==================================+
| BCE Lookup Key: (MN-Identifier) |
+=====================================================================+
Figure 9: BCE Lookup Using Mobile Node Identifier
If there is no Home Network Prefix option present in the request with
a NON_ZERO prefix value and if there is also no Mobile Node Link-
layer Identifier option present in the request, then the following
considerations MUST be applied for locating the Binding Cache entry.
1. The local mobility anchor MUST verify if there exists one and
only one Binding Cache entry with the mobile node identifier
matching the identifier in the Mobile Node Identifier option
present in the request.
2. If there exists only one such entry (matching the MN-Identifier)
and the Handoff Indicator field in the Handoff Indicator option
present in the request is set to a value of 2 (Handoff between
two different interfaces of the mobile node) or set to a value of
3 (Handoff between mobile access gateways for the same
interface), then the request MUST be considered as a request for
updating that Binding Cache entry.
3. If there exists only one such entry (matching the MN-Identifier)
and the Handoff Indicator field in the Handoff Indicator option
present in the request is set to a value of 4 (Handoff state
unknown), the local mobility anchor SHOULD wait until the
existing Binding Cache entry is de-registered by the previously
serving mobile access gateway before the request can be
considered as a request for updating that Binding Cache entry.
However, if there is no de-registration message that is received
within MaxDelayBeforeNewBCEAssign amount of time, the local
mobility anchor, upon accepting the request, MUST consider the
request as a request for creating a new mobility session. The
local mobility anchor MAY also choose to create a new mobility
session without waiting for a de-registration message, and this
should be configurable on the local mobility anchor.
4. For all other cases, the message MUST be considered as a request
for creating a new mobility session. However, if the received
Proxy Binding Update message has the lifetime value of zero and
if the request cannot be associated with any existing mobility
session, the message MUST be silently ignored.
5.5. Timestamp Option for Message Ordering
Mobile IPv6 [RFC3775] 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 mechanisms such as context transfer between the
mobile access gateways, 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 [RFC3775], will be insufficient for Proxy Mobile IPv6.
If the local mobility anchor cannot determine the sending order of
the received Proxy Binding Update messages, it may potentially
process an older message sent by a mobile access gateway where the
mobile node was previously anchored, but delivered out of order,
resulting in incorrectly updating the mobile node's Binding Cache
entry and creating a routing state for tunneling the mobile node's
traffic to the previous mobile access gateway.
For solving this problem, this specification adopts two alternative
solutions. One is based on timestamps and the other based on
sequence numbers, as defined in [RFC3775].
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. The timestamp-based solution may be used when the
serving mobile access gateways in a Proxy Mobile IPv6 domain do not
have the ability to obtain the last sequence number that was sent in
a Proxy Binding Update message for updating a given mobile node's
binding.
Clock drift reduces the effectiveness of the timestamp mechanism.
The time required for reconnection is the total of the time required
for the mobile node to roam between two mobile access gateways and
the time required for the serving mobile access gateway to detect the
mobile node on its access link and construct the Proxy Binding Update
message. If the clock skew on any one of these two neighboring
mobile access gateways (relative to the common time source used for
clock synchronization) is more than half this reconnection time, the
timestamp solution will not predictably work in all cases and hence
SHOULD NOT be used.
As an alternative to the Timestamp-based approach, the specification
also allows the use of Sequence-Number-based scheme, as specified in
[RFC3775]. However, for this scheme to work, the serving mobile
access gateway in a Proxy Mobile IPv6 domain MUST have the ability to
obtain the last sequence number that was sent in a binding
registration message. The sequence number MUST be maintained on a
per mobile node basis and MUST be available to the serving mobile
access gateway. This may be achieved by using context transfer
schemes or by maintaining the sequence number in a policy store.
However, the specific details on how the mobile node's sequence
number is made available to the serving mobile access gateway prior
to sending the Proxy Binding Update message is outside the scope of
this document.
Using the Timestamp-Based Approach:
1. A local mobility anchor implementation MUST support the Timestamp
option. If the Timestamp option is present in the received Proxy
Binding Update 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.
2. All the mobility entities in a Proxy Mobile IPv6 domain that are
exchanging binding registration messages using the Timestamp
option MUST have adequately synchronized time-of-day clocks.
This is the essential requirement for this solution to work. If
this requirement is not met, the solution will not predictably
work in all cases.
3. The mobility entities in a Proxy Mobile IPv6 domain SHOULD
synchronize their clocks to a common time source. For
synchronizing the clocks, the nodes MAY use the Network Time
Protocol [RFC4330]. Deployments MAY also adopt other approaches
suitable for that specific deployment. Alternatively, if there
is a mobile node generated timestamp that is increasing at every
attachment to the access link and if that timestamp is available
to the mobile access gateway (e.g., the Timestamp option in the
SEND [RFC3971] messages that the mobile node sends), the mobile
access gateway can use this timestamp or sequence number in the
Proxy Binding Update messages and does not have to depend on any
external clock source. However, the specific details on how this
is achieved are outside the scope of this document.
4. 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 8.8).
5. 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.
6. 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
following MUST be true.
* The timestamp value contained in the Timestamp option MUST be
close enough (within TimestampValidityWindow amount of time
difference) to the local mobility anchor's time-of-day clock.
However, if the flag MobileNodeGeneratedTimestampInUse is set
to a value of 1, the local mobility anchor MUST ignore this
check and perform only the following check.
* The timestamp MUST be greater than all previously accepted
timestamps in the Proxy Binding Update messages sent for that
mobile node.
7. If the timestamp value in the received Proxy Binding Update is
valid (validity as specified in the above considerations) or if
the flag MobileNodeGeneratedTimestampInUse is set to value of 1,
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.
8. If the timestamp value in the received Proxy Binding Update is
lower than the previously accepted timestamp in the Proxy Binding
Update messages sent for that mobility binding, the local
mobility anchor MUST reject the Proxy Binding Update message and
send a Proxy Binding Acknowledgement message with the Status
field set to TIMESTAMP_LOWER_THAN_PREV_ACCEPTED (Timestamp lower
than previously accepted timestamp). The message MUST also
include the Timestamp option with the value set to the current
time of day on the local mobility anchor.
9. If the timestamp value in the received Proxy Binding Update is
not valid (validity as specified in the above considerations),
the local mobility anchor MUST reject the Proxy Binding Update
and send a Proxy Binding Acknowledgement message with the 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 the Sequence-Number-Based Approach:
1. If the Timestamp option is not present in the received Proxy
Binding Update message, the local mobility anchor MUST fall back
to the Sequence-Number-based scheme. It MUST process the
sequence number field as specified in [RFC3775]. Also, it MUST
NOT include the Timestamp option in the Proxy Binding
Acknowledgement messages that it sends to the mobile access
gateway.
2. An implementation MUST support the Sequence-Number-based scheme,
as specified in [RFC3775].
3. The Sequence-Number-based approach can be used only when there is
some mechanism (such as context transfer procedure between mobile
access gateways) that allows the serving mobile access gateway to
obtain the last sequence number that was sent in a Proxy Binding
Update message for updating a given mobile node's binding.
5.6. Routing Considerations
5.6.1. Bi-Directional Tunnel Management
The bi-directional tunnel MUST be used for routing the mobile node's
data traffic between the mobile access gateway and the local mobility
anchor. A tunnel hides the topology and enables a mobile node to use
address(es) from its home network prefix(es) from any access link in
that Proxy Mobile IPv6 domain. A tunnel may be created dynamically
when needed and removed when not needed. However, implementations
MAY choose to use static pre-established tunnels instead of
dynamically creating and tearing them down on a need basis. The
following considerations MUST be applied when using dynamic tunnels.
o A bi-directional tunnel MUST be established between the local
mobility anchor and the mobile access gateway with IPv6-in-IPv6
encapsulation, as described in [RFC2473]. The tunnel endpoints
are the Proxy-CoA and LMAA. However, when using IPv4 transport,
the endpoints of the tunnel are IPv4-LMAA and IPv4-Proxy-CoA with
the encapsulation mode as specified in [IPV4-PMIP6].
o Implementations MAY 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 can be set to the
accepted binding lifetime and can be updated after each periodic
re-registration for extending the lifetime. If the tunnel is
shared for multiple mobile nodes, the tunnel lifetime must be set
to the highest binding lifetime that is granted to any one of
those mobile nodes sharing that tunnel.
o The tunnel SHOULD be deleted when either the tunnel lifetime
expires or when there are no mobile nodes sharing the tunnel.
5.6.2. 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
the mobile node's home network prefix(es) 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 the mobile node's home network prefix(es).
Forwarding Packets to the Mobile Node:
o On receiving a packet from a correspondent node with the
destination address matching a mobile node's home network
prefix(es), the local mobility anchor MUST forward the packet
through the bi-directional tunnel set up for that mobile node.
o The format of the tunneled packet is shown below. Considerations
from [RFC2473] MUST be applied for IPv6 encapsulation. However,
when using IPv4 transport, the format of the packet is as
described in [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 10: Tunneled Packet from LMA to MAG
o The format of the tunneled packet is shown below, when payload
protection using IPsec is enabled for the mobile node's data
traffic. However, when using IPv4 transport, the format of the
packet is as described in [IPV4-PMIP6].
IPv6 header (src= LMAA, dst= Proxy-CoA /* Tunnel Header */
ESP Header in tunnel mode /* ESP Header */
IPv6 header (src= CN, dst= MN-HoA ) /* Packet Header */
Upper layer protocols /* Packet Content*/
Figure 11: Tunneled Packet from LMA to MAG with Payload Protection
Forwarding Packets Sent by the Mobile Node:
o All the reverse tunneled packets that the local mobility anchor
received 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. Considerations from
[RFC2473] MUST be applied for IPv6 decapsulation.
5.6.3. Explicit Congestion Notification (ECN) Considerations for Proxy
Mobile IPv6 Tunnels
This section describes how the ECN information needs to be handled by
the mobility agents at the tunnel entry and exit points. The ECN
considerations for IP tunnels are specified in [RFC3168], and the
same considerations apply to Proxy Mobile IPv6 tunnels (using IPv6-
in-IPv6 encapsulation mode). Specifically, the full-functionality
option MUST be supported. The relevant ECN considerations from
[RFC3168] are summarized here for convenience.
Encapsulation Considerations:
o If the Explicit Congestion Notification (ECN) field in the inner
header is set to ECT(0) or ECT(1), where ECT stands for ECN-
Capable Transport (ECT), the ECN field from the inner header MUST
be copied to the outer header. Additionally, when payload
protection using IPsec is enabled for the mobile node's data
traffic, the ECN considerations from [RFC4301] MUST be applied.
Decapsulation Considerations:
o If the Explicit Congestion Notification (ECN) field in the inner
header is set to ECT(0) or ECT(1), and if the ECN field in the
outer header is set to Congestion Experienced (CE), then the ECN
field in the inner header MUST be set to CE. Otherwise, the ECN
field in the inner header MUST NOT be modified. Additionally,
when payload protection using IPsec is enabled for the mobile
node's data traffic, the ECN considerations from [RFC4301] MUST be
applied.
5.7. Local Mobility Anchor Address Discovery
Dynamic Home Agent Address Discovery (DHAAD), as explained in Section
10.5 of [RFC3775], 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-Agent's Home Agent's 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-Agent's Home Agent's
anycast address corresponding to the mobile node's home network
prefix(es), as the prefix(es) is not hosted on any of its interfaces.
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.
5.8. Mobile Prefix Discovery Considerations
This specification does not support mobile prefix discovery. The
mobile prefix discovery mechanism as specified in [RFC3775] is not
applicable to Proxy Mobile IPv6.
5.9. Route Optimization Considerations
The Route Optimization in Mobile IPv6, as defined in [RFC3775],
enables a mobile node to communicate with a correspondent node
directly using its Care-of Address care-of address and further the Return Routability
procedure enables the correspondent node to have reasonable trust
that the mobile node is reachable at both its home address and
Care-of Address.
care-of address.
This specification does not support the Route Optimization specified
in Mobile IPv6 [RFC3775]. However, this specification does support
some other form of route optimization, as specified in Section
6.10.3.
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
mobile node's movements to and from the access link and sending the
Proxy Binding Update messages 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 are 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 Advertisement messages containing the mobile node's
home network prefix(es), each prefix carried using the Prefix
Information option [RFC4861].
o Responsible for setting up the forwarding for enabling the mobile
node to configure one or more addresses from its home network
prefix(es) and use it from the attached 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 of
[RFC3775].
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 through mechanisms outside the scope of this document.
o The link-layer identifier of the mobile node's connected
interface. This can be acquired from the received Router
Solicitation messages from the mobile node or during the mobile
node's attachment to the access network. This is typically a
link-layer identifier conveyed by the mobile node; however, the
specific details on how that is conveyed is out of scope for this
specification. If this identifier is not available, this variable
length field MUST be set to two (octets) and MUST be initialized
to a value of ALL_ZERO.
o A list of IPv6 home network prefixes assigned to the mobile node's
connected interface. The home network prefix(es) may have been
statically configured in the mobile node's policy profile, or, may
have been dynamically allocated by the local mobility anchor.
Each of these prefix entries will also include the corresponding
prefix length.
o The Link-local address of the mobile access gateway on the access
link shared with the mobile node.
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 or from other means.
o The interface identifier (if-id) of the point-to-point link
between the mobile node and the mobile access gateway. This is
internal to the mobile access gateway and is used to associate the
Proxy Mobile IPv6 tunnel to the access link where the mobile node
is attached.
o The tunnel interface identifier (tunnel-if-id) of the bi-
directional tunnel between the mobile node's local mobility anchor
and the mobile access gateway. This is internal to 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 or the serving mobile access gateway MAY be able to
dynamically generate this profile. 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)
The following are the optional fields of the policy profile:
o The mobile node's IPv6 home network prefix(es) assigned to the
mobile node's connected interface. These prefixes have to be
maintained on a per-interface basis. There can be multiple unique
entries for each interface of the mobile node. The specific
details on how the network maintains this association between the
prefix set and the interfaces, specially during the mobility
session handoff between interfaces, is outside the scope of this
document.
o The mobile node's IPv6 home network Prefix lifetime. This
lifetime will be the same for all the hosted prefixes on the link,
as they all are part of one mobility session. This value can also
be the same for all the mobile node's mobility sessions.
o Supported address configuration procedures (Stateful, Stateless,
or both) for the mobile node in the Proxy Mobile IPv6 domain
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.
This protocol may also be used on other link types, as long as the
link is configured in such a way that it emulates point-to-point
delivery between the mobile node and the mobile access gateway for
all the protocol traffic.
It is also necessary to be able to identify mobile nodes attaching to
the link. Requirements relating to this are covered in Section 6.6.
Finally, while this specification can operate without link-layer
indications of node attachment and detachment to the link, the
existence of such indications either on the network or mobile node
side improves the resulting performance.
6.4. Supported Address Configuration Modes
A mobile node in the Proxy Mobile IPv6 domain can configure one or
more global IPv6 addresses on its interface (using Stateless,
Stateful, or manual address autoconfiguration procedures) from the
hosted prefix(es) on that link. 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 to 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 access
link, the mobile node can generate one or more IPv6 addresses from
the hosted prefix(es) by standard IPv6 mechanisms such as Stateless
Autoconfiguration [RFC4862] or Privacy extensions [RFC4941].
When stateful address autoconfiguration is supported on the link, the
mobile node can obtain the address configuration from the DHCP server
located in the Proxy Mobile IPv6 domain, by standard DHCP mechanisms,
as specified in [RFC3315]. The obtained address(es) will be from its
home network prefix(es). Section 6.11 specifies the details on how
this configuration can be achieved.
Additionally, other address configuration mechanisms specific to the
access link between the mobile node and the mobile access gateway may
also be used for delivering the address configuration to the mobile
node. This specification does not modify the behavior of any of the
standard IPv6 address configuration mechanisms.
6.5. Access Authentication and 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
security service are outside the scope of this document. This
specification goes with the stated assumption of having an
established trust between the mobile node and the 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 and unique across the Proxy Mobile IPv6 domain. The
mobility entities in the Proxy Mobile IPv6 domain MUST be able to use
this identifier in the signaling messages and unambiguously identify
a given mobile node. The following are some of the considerations
related to this MN-Identifier.
o The MN-Identifier is typically obtained as part of the access
authentication or from a notified network attachment event. In
cases where the user identifier authenticated during access
authentication uniquely identifies a mobile node, the MN-
Identifier MAY be the same as the user identifier. However, the
user identifier MUST NOT be used if it identifies a user account
that can be used from more than one mobile node operating in the
same Proxy Mobile IPv6 domain.
o In some cases, the obtained identifier, as part of the access
authentication, can be a temporary identifier and further that
temporary identifier may be different at each re-authentication.
However, the mobile access gateway MUST be able to use this
temporary identifier and obtain the mobile node's stable
identifier from the policy store. For instance, in AAA-based
systems, the Remote Authentication Dial-In User Service (RADIUS)
attribute, Chargeable-User-Identifier [RFC4372] may be used, as
long as it uniquely identifies a mobile node, and not a user
account that can be used with multiple mobile nodes.
o In some cases and for privacy reasons, 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 to identify the mobile node
by its MN-Identifier, and it MUST be able to associate this
identity to the point-to-point link shared with the mobile node.
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 does not detect any change with respect to its layer-3
attachment even after it changes its point of attachment in 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 Advertisement
messages advertising the mobile node's home network prefix(es)
carried using the Prefix Information option(s) [RFC4861] and with
other address configuration parameters consistent with its home link
properties. Typically, these configuration settings will be based on
the domain-wide policy or based on a policy specific to each mobile
node.
Typically, the mobile access gateway learns the mobile node's home
network prefix(es) details from the received Proxy Binding
Acknowledgement message, or it may obtain them 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(es) only after successfully completing the binding
registration with the mobile node's local mobility anchor.
When advertising the home network prefix(es) in the Router
Advertisement messages, the mobile access gateway MAY set the prefix
lifetime value for the advertised prefix(es) to any chosen value at
its own discretion. An implementation MAY choose to tie the prefix
lifetime to the mobile node's binding lifetime. The prefix lifetime
can also be an optional configuration parameter in the mobile node's
policy profile.
6.8. Link-Local 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, will continue to detect its home
network and does not detect a change of layer-3 attachment. 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
Duplicate Address Detection (DAD) operation on the link-local and
global address(es). However, if the mobile node is Detecting Network
Attachment in IPv6 (DNAv6) enabled, as specified in [DNAV6], it may
not detect the link change due to DNAv6 optimizations and may not
trigger the duplicate address detection (DAD) procedure for its
existing addresses, which may potentially lead to address collisions
after the mobile node's handoff to a new link.
The issue of address collision is not relevant to the mobile node's
global address(es). Since the assigned home network prefix(es) are
for the mobile node's exclusive usage, no other node shares an
address (other than Subnet-Router anycast address that is configured
by the mobile access gateway) from the prefix(es), and so the
uniqueness for the mobile node's global address is assured on the
access link.
The issue of address collision is however relevant to the mobile
node's link-local addresses since the mobile access gateway and the
mobile node will have link-local addresses configured from the same
link-local prefix (FE80::/64). This leaves a room for link-local
address collision between the two neighbors (i.e., the mobile node
and the mobile access gateway) on that access link. For solving this
problem, this specification requires that the link-local address that
the mobile access gateway configures on the point-to-point link
shared with a given mobile node be generated by the local mobility
anchor and be stored in the mobile node's Binding Cache entry. This
address will not change for the duration of that mobile node's
mobility session and can be provided to the serving mobile access
gateway at every mobile node's handoff, as part of the Proxy Mobile
IPv6 signaling messages. The specific method by which the local
mobility anchor generates the link-local address is out of scope for
this specification.
It is highly desirable that the access link on the mobile access
gateway shared with the mobile node be provisioned in such a way that
before the mobile node completes the DAD operation [RFC4862] on its
link-local address, the mobile access gateway on that link is aware
of its own link-local address provided by the local mobility anchor
that it needs to use on that access link. This essentially requires
a successful completion of the Proxy Mobile IPv6 signaling by the
mobile access gateway before the mobile node completes the DAD
operation. This can be achieved by ensuring that link-layer
attachment does not complete until the Proxy Mobile IPv6 signaling is
completed. Alternatively, network and local mobility anchor capacity
and signaling retransmission timers can be provisioned in such a way
that signaling is extremely likely to complete during the default
waiting period associated with the DAD process.
Optionally, implementations MAY choose to configure a fixed link-
local address across all the access links in a Proxy Mobile IPv6
domain and without a need for carrying this address from the local
mobility anchor to the mobile access gateway in the Proxy Mobile IPv6
signaling messages. The configuration variable
FixedMAGLinkLocalAddressOnAllAccessLinks determines the enabled mode
in that Proxy Mobile IPv6 domain.
6.9. Signaling Considerations
6.9.1. Binding Registrations
6.9.1.1. Mobile Node Attachment and Initial Binding Registration
1. 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 be offered to the mobile node, it
MUST send a Proxy Binding Update message to the local mobility
anchor.
2. The Proxy Binding Update message MUST include the Mobile Node
Identifier option [RFC4283], carrying the MN-Identifier for
identifying the mobile node.
3. The Home Network Prefix option(s) MUST be present in the Proxy
Binding Update message. If the mobile access gateway learns the
mobile node's home network prefix(es) either from its policy
store or from other means, the mobile access gateway MAY choose
to request the local mobility anchor to allocate the requested
prefix(es) by including a Home Network Prefix option for each of
those requested prefixes. The mobile access gateway MAY also
choose to include just one Home Network Prefix option with the
prefix value of ALL_ZERO, for requesting the local mobility
anchor to do the prefix assignment. However, when including a
Home Network Prefix option with the prefix value of ALL_ZERO,
there MUST be only one instance of the Home Network prefix
option in the request.
4. The Handoff Indicator option MUST be present in the Proxy
Binding Update message. The Handoff Indicator field in the
Handoff Indicator option MUST be set to a value indicating the
handoff hint.
* The Handoff Indicator field MUST be set to a value of 1
(Attachment over a new interface) if the mobile access
gateway determines (under the Handoff Indicator
considerations specified in this section) that the mobile
node's current attachment to the network over this interface
is not as a result of a handoff of an existing mobility
session (over the same interface or through a different
interface), but as a result of an attachment over a new
interface. This essentially serves as a request to the local
mobility anchor to create a new mobility session and not
update any existing Binding Cache entry created for the same
mobile node connected to the Proxy Mobile IPv6 domain through
a different interface.
* The Handoff Indicator field MUST be set to a value of 2
(Handoff between two different interfaces of the mobile node)
if the mobile access gateway definitively knows the mobile
node's current attachment is due to a handoff of an existing
mobility session between two different interfaces of the
mobile node.
* The Handoff Indicator field MUST be set to a value of 3
(Handoff between mobile access gateways for the same
interface) if the mobile access gateway definitively knows
the mobile node's current attachment is due to a handoff of
an existing mobility session between two mobile access
gateways and for the same interface of the mobile node.
* The Handoff Indicator field MUST be set to a value of 4
(Handoff state unknown) if the mobile access gateway cannot
determine if the mobile node's current attachment is due to a
handoff of an existing mobility session.
5. The mobile access gateway MUST apply the below considerations
when choosing the value for the Handoff Indicator field.
* The mobile access gateway can choose to use the value 2
(Handoff between two different interfaces of the mobile
node), only when it knows that the mobile node has, on
purpose, switched from one interface to another, and the
previous interface is going to be disabled. It may know this
due to a number of factors. For instance, most cellular
networks have controlled handovers where the network knows
that the host is moving from one attachment to another. In
this situation, the link-layer mechanism can inform the
mobility functions that this is indeed a movement, not a new
attachment.
* Some link layers have link-layer identifiers that can be used
to distinguish (a) the movement of a particular interface to
a new attachment from (b) the attachment of a new interface
from the same host. Option value 3 (Handoff between mobile
access gateways for the same interface) is appropriate in
case (a) and a value of 1 (Attachment over a new interface)
in case (b).
* The mobile access gateway MUST NOT set the option value to 2
(Handoff between two different interfaces of the mobile node)
or 3 (Handoff between mobile access gateways for the same
interface) if it cannot be determined that the mobile node
can move the address between the interfaces involved in the
handover or that it is the same interface that has moved.
Otherwise, Proxy Mobile IPv6-unaware hosts that have multiple
physical interfaces to the same domain may suffer unexpected
failures.
* Where no support from the link layer exists, the host and the
network would need to inform each other about the intended
movement. The Proxy Mobile IPv6 protocol does not specify
this and simply requires that knowledge about movements can
be derived either from the link-layer or from somewhere else.
The method by which this is accomplished is outside the scope
of this specification.
6. Either the Timestamp option or a valid sequence number
maintained on a per mobile node basis (if the Sequence-Number-
based scheme is in use) MUST be present. This can be determined
based on the value of the configuration flag
TimestampBasedApproachInUse. When Timestamp option is added to
the message, the mobile access gateway SHOULD also set the
Sequence Number field to a value of a monotonically increasing
counter (not to be confused with the per mobile node sequence
number specified in [RFC3775]). The local mobility anchor will
ignore this field when there is a Timestamp option present in
the request, but will return the same value in the Proxy Binding
Acknowledgement message. This will be useful for matching the
reply to the request message.
7. The Mobile Node Link-layer Identifier option carrying the link-
layer identifier of the currently attached interface MUST be
present in the Proxy Binding Update message, if the mobile
access gateway is aware of the same. If the link-layer
identifier of the currently attached interface is not known or
if the identifier value is ALL_ZERO, this option MUST NOT be
present.
8. The Access Technology Type option MUST be present in the Proxy
Binding Update message. The access technology type field in the
option SHOULD be set to the type of access technology by which
the mobile node is currently attached to the mobile access
gateway.
9. The Link-local Address option MUST be present in the Proxy
Binding Update message only if the value of the configuration
variable FixedMAGLinkLocalAddressOnAllAccessLinks is set to a
value of ALL_ZERO; otherwise, the Link-local Address option MUST
NOT be present in the request. Considerations from Section 6.8
MUST be applied when using the Link-local Address option.
* For querying the local mobility anchor to provide the link-
local address that it should use on the point-to-point link
shared with the mobile node, this option MUST be set to
ALL_ZERO value. This essentially serves as a request to the
local mobility anchor to provide the link-local address that
it can use on the access link shared with the mobile node.
10. The Proxy Binding Update message MUST be constructed as
specified in Section 6.9.1.5.
11. If there is no existing Binding Update List entry for that
mobile node, the mobile access gateway MUST create a Binding
Update List entry for the mobile node upon sending the Proxy
Binding Update message.
6.9.1.2. Receiving Proxy Binding Acknowledgement
On receiving a Proxy Binding Acknowledgement message (format
specified in Section 8.2) from the local mobility anchor, the mobile
access gateway MUST process the message as specified below.
1. The received Proxy Binding Acknowledgement message (a Binding
Acknowledgement message with the 'P' flag set to value of 1)
MUST be authenticated as described in Section 4. When IPsec is
used for message authentication, the SPI in the IPsec header
[RFC4306] of the received packet is needed for locating the
security association, for authenticating the Proxy Binding
Acknowledgement message.
2. The mobile access gateway MUST observe the rules described in
Section 9.2 of [RFC3775] when processing Mobility Headers in the
received Proxy Binding Acknowledgement message.
3. The mobile access gateway MUST apply the considerations
specified in Section 5.5 for processing the Sequence Number
field and the Timestamp option (if present) in the message.
4. The mobile access gateway MUST ignore any checks, specified in
[RFC3775], related to the presence of a Type 2 Routing header in
the Proxy Binding Acknowledgement message.
5. The mobile access gateway MAY use the mobile node identifier
present in the Mobile Node Identifier option for matching the
response to the request messages that it sent recently.
However, if there is more than one request message in its
request queue for the same mobile node, the sequence number
field can be used for identifying the exact message from those
messages. There are other ways to achieve this and
implementations are free to adopt the best approach that suits
their implementation. Additionally, if the received Proxy
Binding Acknowledgement message does not match any of the Proxy
Binding Update messages that it sent recently, the message MUST
be ignored.
6. If the received Proxy Binding Acknowledgement message h