RFC 6275
Mobility Support in IPv6
Internet Engineering Task Force (IETF) C. Perkins, Ed. Request for Comments: 6275 Tellabs, Inc. Obsoletes: 3775 D. Johnson Category: Standards Track Rice University ISSN: 2070-1721 J. Arkko Ericsson July 2011 Mobility Support in IPv6Abstract
This document specifies Mobile IPv6, a protocol that allows nodes to remain reachable while moving around in the IPv6 Internet. Each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet. While situated away from its home, a mobile node is also associated with a care-of address, which provides information about the mobile node's current location. IPv6 packets addressed to a mobile node's home address are transparently routed to its care-of address. The protocol enables IPv6 nodes to cache the binding of a mobile node's home address with its care-of address, and to then send any packets destined for the mobile node directly to it at this care-of address. To support this operation, Mobile IPv6 defines a new IPv6 protocol and a new destination option. All IPv6 nodes, whether mobile or stationary, can communicate with mobile nodes. This document obsoletes RFC 3775. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6275.
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Table of Contents
1. Introduction ....................................................7 2. Comparison with Mobile IP for IPv4 ..............................8 3. Terminology .....................................................9 3.1. General Terms ..............................................9 3.2. Mobile IPv6 Terms .........................................11 4. Overview of Mobile IPv6 ........................................15 4.1. Basic Operation ...........................................15 4.2. New IPv6 Protocol .........................................17 4.3. New IPv6 Destination Option ...............................18 4.4. New IPv6 ICMP Messages ....................................19 4.5. Conceptual Data Structure Terminology .....................19 4.6. Unique-Local Addressability ...............................20 5. Overview of Mobile IPv6 Security ...............................20 5.1. Binding Updates to Home Agents ............................21 5.2. Binding Updates to Correspondent Nodes ....................22 5.2.1. Node Keys ..........................................22 5.2.2. Nonces .............................................23 5.2.3. Cookies and Tokens .................................23 5.2.4. Cryptographic Functions ............................24 5.2.5. Return Routability Procedure .......................24 5.2.6. Authorizing Binding Management Messages ............28 5.2.7. Updating Node Keys and Nonces ......................30 5.2.8. Preventing Replay Attacks ..........................32 5.2.9. Handling Interruptions to Return Routability .......32 5.3. Dynamic Home Agent Address Discovery ......................33 5.4. Mobile Prefix Discovery ...................................33 5.5. Payload Packets ...........................................33 6. New IPv6 Protocol, Message Types, and Destination Option .......34 6.1. Mobility Header ...........................................34 6.1.1. Format .............................................34 6.1.2. Binding Refresh Request Message ....................36 6.1.3. Home Test Init Message .............................37 6.1.4. Care-of Test Init Message ..........................38 6.1.5. Home Test Message ..................................39 6.1.6. Care-of Test Message ...............................41 6.1.7. Binding Update Message .............................42 6.1.8. Binding Acknowledgement Message ....................44 6.1.9. Binding Error Message ..............................47 6.2. Mobility Options ..........................................48 6.2.1. Format .............................................49 6.2.2. Pad1 ...............................................49 6.2.3. PadN ...............................................50 6.2.4. Binding Refresh Advice .............................50 6.2.5. Alternate Care-of Address ..........................51 6.2.6. Nonce Indices ......................................52 6.2.7. Binding Authorization Data .........................52
6.3. Home Address Option .......................................54
6.4. Type 2 Routing Header .....................................55
6.4.1. Format .............................................56
6.5. ICMP Home Agent Address Discovery Request Message .........57
6.6. ICMP Home Agent Address Discovery Reply Message ...........58
6.7. ICMP Mobile Prefix Solicitation Message Format ............60
6.8. ICMP Mobile Prefix Advertisement Message Format ...........61
7. Modifications to IPv6 Neighbor Discovery .......................64
7.1. Modified Router Advertisement Message Format ..............64
7.2. Modified Prefix Information Option Format .................65
7.3. New Advertisement Interval Option Format ..................66
7.4. New Home Agent Information Option Format ..................67
7.5. Changes to Sending Router Advertisements ..................69
8. Requirements for Types of IPv6 Nodes ...........................71
8.1. All IPv6 Nodes ............................................71
8.2. IPv6 Nodes with Support for Route Optimization ............72
8.3. All IPv6 Routers ..........................................73
8.4. IPv6 Home Agents ..........................................74
8.5. IPv6 Mobile Nodes .........................................75
9. Correspondent Node Operation ...................................76
9.1. Conceptual Data Structures ................................76
9.2. Processing Mobility Headers ...............................78
9.3. Packet Processing .........................................78
9.3.1. Receiving Packets with Home Address Option .........78
9.3.2. Sending Packets to a Mobile Node ...................79
9.3.3. Sending Binding Error Messages .....................81
9.3.4. Receiving ICMP Error Messages ......................81
9.4. Return Routability Procedure ..............................82
9.4.1. Receiving Home Test Init Messages ..................82
9.4.2. Receiving Care-of Test Init Messages ...............82
9.4.3. Sending Home Test Messages .........................83
9.4.4. Sending Care-of Test Messages ......................83
9.5. Processing Bindings .......................................83
9.5.1. Receiving Binding Updates ..........................83
9.5.2. Requests to Cache a Binding ........................86
9.5.3. Requests to Delete a Binding .......................86
9.5.4. Sending Binding Acknowledgements ...................87
9.5.5. Sending Binding Refresh Requests ...................88
9.6. Cache Replacement Policy ..................................88
10. Home Agent Operation ..........................................89
10.1. Conceptual Data Structures ...............................89
10.2. Processing Mobility Headers ..............................90
10.3. Processing Bindings ......................................90
10.3.1. Primary Care-of Address Registration ..............90
10.3.2. Primary Care-of Address De-Registration ...........94
10.4. Packet Processing ........................................96
10.4.1. Intercepting Packets for a Mobile Node ............96
10.4.2. Processing Intercepted Packets ....................98
10.4.3. Multicast Membership Control ......................99
10.4.4. Stateful Address Autoconfiguration ...............100
10.4.5. Handling Reverse-Tunneled Packets ................100
10.4.6. Protecting Return Routability Packets ............101
10.5. Dynamic Home Agent Address Discovery ....................102
10.5.1. Receiving Router Advertisement Messages ..........102
10.6. Sending Prefix Information to the Mobile Node ...........104
10.6.1. List of Home Network Prefixes ....................104
10.6.2. Scheduling Prefix Deliveries .....................105
10.6.3. Sending Advertisements ...........................107
10.6.4. Lifetimes for Changed Prefixes ...................108
11. Mobile Node Operation ........................................108
11.1. Conceptual Data Structures ..............................108
11.2. Processing Mobility Headers .............................110
11.3. Packet Processing .......................................110
11.3.1. Sending Packets While Away from Home .............110
11.3.2. Interaction with Outbound IPsec Processing .......113
11.3.3. Receiving Packets While Away from Home ...........115
11.3.4. Routing Multicast Packets ........................117
11.3.5. Receiving ICMP Error Messages ....................118
11.3.6. Receiving Binding Error Messages .................119
11.4. Home Agent and Prefix Management ........................120
11.4.1. Dynamic Home Agent Address Discovery .............120
11.4.2. Sending Mobile Prefix Solicitations ..............121
11.4.3. Receiving Mobile Prefix Advertisements ...........121
11.5. Movement ................................................123
11.5.1. Movement Detection ...............................123
11.5.2. Home Link Detection ..............................125
11.5.3. Forming New Care-of Addresses ....................126
11.5.4. Using Multiple Care-of Addresses .................127
11.5.5. Returning Home ...................................127
11.6. Return Routability Procedure ............................130
11.6.1. Sending Test Init Messages .......................130
11.6.2. Receiving Test Messages ..........................131
11.6.3. Protecting Return Routability Packets ............132
11.7. Processing Bindings .....................................132
11.7.1. Sending Binding Updates to the Home Agent ........132
11.7.2. Correspondent Registration .......................135
11.7.3. Receiving Binding Acknowledgements ...............138
11.7.4. Receiving Binding Refresh Requests ...............140
11.8. Retransmissions and Rate Limiting .......................141
12. Protocol Constants ...........................................142
13. Protocol Configuration Variables .............................142
14. IANA Considerations ..........................................143
15. Security Considerations ......................................146
15.1. Threats .................................................146
15.2. Features ................................................148
15.3. Binding Updates to Home Agent ...........................150
15.4. Binding Updates to Correspondent Nodes ..................152
15.4.1. Overview .........................................153
15.4.2. Achieved Security Properties .....................153
15.4.3. Comparison to Regular IPv6 Communications ........154
15.4.4. Replay Attacks ...................................156
15.4.5. Denial-of-Service Attacks ........................156
15.4.6. Key Lengths ......................................157
15.5. Dynamic Home Agent Address Discovery ....................158
15.6. Mobile Prefix Discovery .................................159
15.7. Tunneling via the Home Agent ............................159
15.8. Home Address Option .....................................160
15.9. Type 2 Routing Header ...................................161
15.10. SHA-1 Secure Enough for Mobile IPv6 Control Messages ...161
16. Contributors .................................................162
17. Acknowledgements .............................................162
18. References ...................................................162
18.1. Normative References ....................................162
18.2. Informative References ..................................164
Appendix A. Future Extensions ....................................166
A.1. Piggybacking .............................................166
A.2. Triangular Routing .......................................166
A.3. New Authorization Methods ................................166
A.4. Neighbor Discovery Extensions ............................166
Appendix B. Changes since RFC 3775 ...............................167
1. Introduction
This document specifies a protocol that allows nodes to remain reachable while moving around in the IPv6 Internet. Without specific support for mobility in IPv6 [6], packets destined to a mobile node would not be able to reach it while the mobile node is away from its home link. In order to continue communication in spite of its movement, a mobile node could change its IP address each time it moves to a new link, but the mobile node would then not be able to maintain transport and higher-layer connections when it changes location. Mobility support in IPv6 is particularly important, as mobile computers are likely to account for a majority or at least a substantial fraction of the population of the Internet during the lifetime of IPv6. The protocol defined in this document, known as Mobile IPv6, allows a mobile node to move from one link to another without changing the mobile node's "home address". Packets may be routed to the mobile node using this address regardless of the mobile node's current point of attachment to the Internet. The mobile node may also continue to communicate with other nodes (stationary or mobile) after moving to a new link. The movement of a mobile node away from its home link is thus transparent to transport and higher-layer protocols and applications. The Mobile IPv6 protocol is just as suitable for mobility across homogeneous media as for mobility across heterogeneous media. For example, Mobile IPv6 facilitates node movement from one Ethernet segment to another as well as it facilitates node movement from an Ethernet segment to a wireless LAN cell, with the mobile node's IP address remaining unchanged in spite of such movement. One can think of the Mobile IPv6 protocol as solving the network- layer mobility management problem. Some mobility management applications -- for example, handover among wireless transceivers, each of which covers only a very small geographic area -- have been solved using link-layer techniques. For example, in many current wireless LAN products, link-layer mobility mechanisms allow a "handover" of a mobile node from one cell to another, re-establishing link-layer connectivity to the node in each new location. Mobile IPv6 does not attempt to solve all general problems related to the use of mobile computers or wireless networks. In particular, this protocol does not attempt to solve: o Handling links with unidirectional connectivity or partial reachability, such as the hidden terminal problem where a host is hidden from only some of the routers on the link.
o Access control on a link being visited by a mobile node.
o Local or hierarchical forms of mobility management (similar to
many current link-layer mobility management solutions).
o Assistance for adaptive applications.
o Mobile routers.
o Service discovery.
o Distinguishing between packets lost due to bit errors versus
network congestion.
This document obsoletes RFC 3775. Issues with the original document
have been observed during the integration, testing, and deployment of
RFC 3775. A more detailed list of the changes since RFC 3775 may be
found in Appendix B.
2. Comparison with Mobile IP for IPv4
The design of Mobile IP support in IPv6 (Mobile IPv6) benefits both
from the experiences gained from the development of Mobile IP support
in IPv4 (Mobile IPv4) [32] [25] [26], and from the opportunities
provided by IPv6. Mobile IPv6 thus shares many features with Mobile
IPv4, but is integrated into IPv6 and offers many other improvements.
This section summarizes the major differences between Mobile IPv4 and
Mobile IPv6:
o There is no need to deploy special routers as "foreign agents", as
in Mobile IPv4. Mobile IPv6 operates in any location without any
special support required from the local router.
o Support for route optimization is a fundamental part of the
protocol, rather than a nonstandard set of extensions.
o Mobile IPv6 route optimization can operate securely even without
pre-arranged security associations. It is expected that route
optimization can be deployed on a global scale between all mobile
nodes and correspondent nodes.
o Support is also integrated into Mobile IPv6 for allowing route
optimization to coexist efficiently with routers that perform
"ingress filtering" [27].
o The IPv6 Neighbor Unreachability Detection ensures symmetric
reachability between the mobile node and its default router in the
current location.
o Most packets sent to a mobile node while away from home in Mobile
IPv6 are sent using an IPv6 routing header rather than IP
encapsulation, reducing the amount of resulting overhead compared
to Mobile IPv4.
o Mobile IPv6 is decoupled from any particular link layer, as it
uses IPv6 Neighbor Discovery [18] instead of the Address
Resolution Protocol (ARP). This also improves the robustness of
the protocol.
o The use of IPv6 encapsulation (and the routing header) removes the
need in Mobile IPv6 to manage "tunnel soft state".
o The dynamic home agent address discovery mechanism in Mobile IPv6
returns a single reply to the mobile node. The directed broadcast
approach used in IPv4 returns separate replies from each home
agent.
3. Terminology
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 [2].
3.1. General Terms
IP
Internet Protocol Version 6 (IPv6).
node
A device that implements IP.
router
A node that forwards IP packets not explicitly addressed to
itself.
unicast routable address
An identifier for a single interface such that a packet sent to it
from another IPv6 subnet is delivered to the interface identified
by that address. Accordingly, a unicast routable address must be
either a global IPv6 address or a unique local IPv6 address.
host
Any node that is not a router.
link
A communication facility or medium over which nodes can
communicate at the link layer, such as an Ethernet (simple or
bridged). A link is the layer immediately below IP.
interface
A node's attachment to a link.
subnet prefix
A bit string that consists of some number of initial bits of an IP
address.
interface identifier
A number used to identify a node's interface on a link. The
interface identifier is the remaining low-order bits in the node's
IP address after the subnet prefix.
link-layer address
A link-layer identifier for an interface, such as IEEE 802
addresses on Ethernet links.
packet
An IP header plus payload.
security association
An IPsec security association is a cooperative relationship formed
by the sharing of cryptographic keying material and associated
context. Security associations are simplex. That is, two
security associations are needed to protect bidirectional traffic
between two nodes, one for each direction.
security policy database
A database that specifies what security services are to be offered
to IP packets and in what fashion.
destination option
Destination options are carried by the IPv6 Destination Options
extension header. Destination options include optional
information that need be examined only by the IPv6 node given as
the destination address in the IPv6 header, not by routers in
between. Mobile IPv6 defines one new destination option, the Home
Address destination option (see Section 6.3).
routing header
A routing header may be present as an IPv6 header extension, and
indicates that the payload has to be delivered to a destination
IPv6 address in some way that is different from what would be
carried out by standard Internet routing. In this document, use
of the term "routing header" typically refers to use of a type 2
routing header, as specified in Section 6.4.
"|" (concatenation)
Some formulas in this specification use the symbol "|" to indicate
bytewise concatenation, as in A | B. This concatenation requires
that all of the octets of the datum A appear first in the result,
followed by all of the octets of the datum B.
First (size, input)
Some formulas in this specification use a functional form "First
(size, input)" to indicate truncation of the "input" data so that
only the first "size" bits remain to be used.
3.2. Mobile IPv6 Terms
These terms are intended to be compatible with the definitions given
in RFC 3753 [40]. However, if there is any conflict, the definitions
given here should be considered to supersede those in RFC 3753.
home address
A unicast routable address assigned to a mobile node, used as the
permanent address of the mobile node. This address is within the
mobile node's home link. Standard IP routing mechanisms will
deliver packets destined for a mobile node's home address to its
home link. Mobile nodes can have multiple home addresses, for
instance, when there are multiple home prefixes on the home link.
home subnet prefix
The IP subnet prefix corresponding to a mobile node's home
address.
home link
The link on which a mobile node's home subnet prefix is defined.
mobile node
A node that can change its point of attachment from one link to
another, while still being reachable via its home address.
movement
A change in a mobile node's point of attachment to the Internet
such that it is no longer connected to the same link as it was
previously. If a mobile node is not currently attached to its
home link, the mobile node is said to be "away from home".
Layer 2 (L2) handover
A process by which the mobile node changes from one link-layer
connection to another. For example, a change of wireless access
point is an L2 handover.
Layer 3 (L3) handover
Subsequent to an L2 handover, a mobile node detects a change in an
on-link subnet prefix that would require a change in the primary
care-of address. For example, a change of access router
subsequent to a change of wireless access point typically results
in an L3 handover.
correspondent node
A peer node with which a mobile node is communicating. The
correspondent node may be either mobile or stationary.
foreign subnet prefix
Any IP subnet prefix other than the mobile node's home subnet
prefix.
foreign link
Any link other than the mobile node's home link.
care-of address
A unicast routable address associated with a mobile node while
visiting a foreign link; the subnet prefix of this IP address is a
foreign subnet prefix. Among the multiple care-of addresses that
a mobile node may have at any given time (e.g., with different
subnet prefixes), the one registered with the mobile node's home
agent for a given home address is called its "primary" care-of
address.
home agent
A router on a mobile node's home link with which the mobile node
has registered its current care-of address. While the mobile node
is away from home, the home agent intercepts packets on the home
link destined to the mobile node's home address, encapsulates
them, and tunnels them to the mobile node's registered care-of
address.
binding
The association of the home address of a mobile node with a
care-of address for that mobile node, along with the remaining
lifetime of that association.
registration
The process during which a mobile node sends a Binding Update to
its home agent or a correspondent node, causing a binding for the
mobile node to be registered.
mobility message
A message containing a Mobility Header (see Section 6.1).
binding authorization
Correspondent registration needs to be authorized to allow the
recipient to believe that the sender has the right to specify a
new binding.
return routability procedure
The return routability procedure authorizes registrations by the
use of a cryptographic token exchange.
correspondent registration
A return routability procedure followed by a registration, run
between the mobile node and a correspondent node.
home registration
A registration between the mobile node and its home agent,
authorized by the use of IPsec.
nonce
Nonces are random numbers used internally by the correspondent
node in the creation of keygen tokens related to the return
routability procedure. The nonces are not specific to a mobile
node, and are kept secret within the correspondent node.
nonce index
A nonce index is used to indicate which nonces have been used when
creating keygen token values, without revealing the nonces
themselves.
cookie
A cookie is a random number used by a mobile node to prevent
spoofing by a bogus correspondent node in the return routability
procedure.
care-of init cookie
A cookie sent to the correspondent node in the Care-of Test Init
message, to be returned in the Care-of Test message.
home init cookie
A cookie sent to the correspondent node in the Home Test Init
message, to be returned in the Home Test message.
keygen token
A keygen token is a number supplied by a correspondent node in the
return routability procedure to enable the mobile node to compute
the necessary binding management key for authorizing a Binding
Update.
care-of keygen token
A keygen token sent by the correspondent node in the Care-of Test
message.
home keygen token
A keygen token sent by the correspondent node in the Home Test
message.
binding management key (Kbm)
A binding management key (Kbm) is a key used for authorizing a
binding cache management message (e.g., Binding Update or Binding
Acknowledgement). Return routability provides a way to create a
binding management key.
(page 15 continued on part 2)
