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rfc:rfc3963

Network Working Group V. Devarapalli Request for Comments: 3963 Nokia Category: Standards Track R. Wakikawa

                                                       Keio University
                                                           A. Petrescu
                                                              Motorola
                                                            P. Thubert
                                                         Cisco Systems
                                                          January 2005
           Network Mobility (NEMO) Basic Support Protocol

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.

Copyright Notice

 Copyright (C) The Internet Society (2005).

Abstract

 This document describes the Network Mobility (NEMO) Basic Support
 protocol that enables Mobile Networks to attach to different points
 in the Internet.  The protocol is an extension of Mobile IPv6 and
 allows session continuity for every node in the Mobile Network as the
 network moves.  It also allows every node in the Mobile Network to be
 reachable while moving around.  The Mobile Router, which connects the
 network to the Internet, runs the NEMO Basic Support protocol with
 its Home Agent.  The protocol is designed so that network mobility is
 transparent to the nodes inside the Mobile Network.

Devarapalli, et al. Standards Track [Page 1] RFC 3963 NEMO Basic Support Protocol January 2005

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . .    3
 2.  Terminology. . . . . . . . . . . . . . . . . . . . . . . . .    4
 3.  Overview of the NEMO Protocol. . . . . . . . . . . . . . . .    4
 4.  Message Formats. . . . . . . . . . . . . . . . . . . . . . .    7
     4.1. Binding Update. . . . . . . . . . . . . . . . . . . . .    7
     4.2. Binding Acknowledgement . . . . . . . . . . . . . . . .    7
     4.3. Mobile Network Prefix Option. . . . . . . . . . . . . .    8
 5.  Mobile Router Operation. . . . . . . . . . . . . . . . . . .    9
     5.1. Data Structures . . . . . . . . . . . . . . . . . . . .   10
     5.2. Sending Binding Updates . . . . . . . . . . . . . . . .   10
     5.3. Receiving Binding Acknowledgements. . . . . . . . . . .   11
     5.4. Error Processing  . . . . . . . . . . . . . . . . . . .   12
          5.4.1. Implicit Mode. . . . . . . . . . . . . . . . . .   12
          5.4.2. Explicit Mode. . . . . . . . . . . . . . . . . .   12
     5.5. Establishment of Bi-directional Tunnel  . . . . . . . .   13
     5.6. Neighbor Discovery for Mobile Router  . . . . . . . . .   13
     5.7. Multicast Groups for Mobile Router  . . . . . . . . . .   14
     5.8. Returning Home  . . . . . . . . . . . . . . . . . . . .   14
 6.  Home Agent Operation . . . . . . . . . . . . . . . . . . . .   15
     6.1. Data Structures . . . . . . . . . . . . . . . . . . . .   15
          6.1.1. Binding Cache. . . . . . . . . . . . . . . . . .   15
          6.1.2. Prefix Table . . . . . . . . . . . . . . . . . .   15
     6.2. Mobile Network Prefix Registration  . . . . . . . . . .   16
     6.3. Advertising Mobile Network Reachability . . . . . . . .   17
     6.4. Establishment of Bi-directional Tunnel  . . . . . . . .   18
     6.5. Forwarding Packets  . . . . . . . . . . . . . . . . . .   18
     6.6. Sending Binding Acknowledgements  . . . . . . . . . . .   19
     6.7. Mobile Network Prefix De-Registration . . . . . . . . .   19
 7.  Modifications to Dynamic Home Agent Address Discovery. . . .   20
     7.1. Modified Dynamic Home Agent Discovery Request . . . . .   20
     7.2. Modified Dynamic Home Agent Discovery Address Request .   20
     7.3. Modified Home Agent Information Option  . . . . . . . .   21
 8.  Support for Dynamic Routing Protocols. . . . . . . . . . . .   22
 9.  Security Considerations. . . . . . . . . . . . . . . . . . .   23
 10. IANA Considerations. . . . . . . . . . . . . . . . . . . . .   24
 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . .   25
 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . .   25
 13. References . . . . . . . . . . . . . . . . . . . . . . . . .   25
 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . .   27
     A. Examples of NEMO Basic Support Operation. . . . . . . . .   27
     B. Running Link State Routing Protocol with NEMO Basic
        Support . . . . . . . . . . . . . . . . . . . . . . . . .   30
        B.1. Tunnel Interface Considerations. . . . . . . . . . .   30
        B.2. OSPF Area Considerations . . . . . . . . . . . . . .   30
 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .   32
 Full Copyright Statement . . . . . . . . . . . . . . . . . . . .   33

Devarapalli, et al. Standards Track [Page 2] RFC 3963 NEMO Basic Support Protocol January 2005

1. Introduction

 This document describes protocol extensions to Mobile IPv6 (MIPv6)
 [1] to enable support for network mobility.  The extensions are
 backward compatible with Mobile IPv6.  In particular, a NEMO-
 compliant Home Agent can operate as a Mobile IPv6 Home Agent.  The
 solution described here satisfies the goals and requirements
 identified in [11] for network mobility.
 The NEMO Basic Support ensures session continuity for all the nodes
 in the Mobile Network, even as the Mobile Router changes its point of
 attachment to the Internet.  It also provides connectivity and
 reachability for all nodes in the Mobile Network as it moves.  The
 solution supports both mobile nodes and hosts that do not support
 mobility in the Mobile Network.
 Within the context of this document, the definition of a Mobile
 Router extends that of a Mobile IPv6 [1] Mobile Node, by adding
 routing capability routing between its point of attachment (Care-of
 Address) and a subnet that moves with the Mobile Router.
 The solution described in this document proposes a bi-directional
 tunnel between the Mobile Router and its Home Agent.  This tunnel is
 set up when the Mobile Router sends a successful Binding Update to
 its Home Agent, informing the Home Agent of its current point of
 attachment.
 All traffic between the nodes in the Mobile Network and Correspondent
 Nodes passes through the Home Agent.  This document does not describe
 route optimization of this traffic.
 The terminology document [10] describes Nested Mobility as a scenario
 where a Mobile Router allows another Mobile Router to attach to its
 Mobile Network.  There could be arbitrary levels of nested mobility.
 The operation of each Mobile Router remains the same whether the
 Mobile Router attaches to another Mobile Router or to a fixed Access
 Router on the Internet.  The solution described here does not place
 any restriction on the number of levels for nested mobility.  But
 note that this might introduce significant overhead on the data
 packets as each level of nesting introduces another IPv6 header
 encapsulation.
 This document does not discuss multihoming for Mobile Routers.

Devarapalli, et al. Standards Track [Page 3] RFC 3963 NEMO Basic Support Protocol January 2005

2. Terminology

 The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in BCP 14, RFC 2119 [7].
 Network Mobility - related terminology is defined in [9] and [10].
 This document in addition defines the following terms.
    Mobile Network Prefix
       An IPv6 prefix delegated to a Mobile Router and advertised in
       the Mobile Network.  More than one Mobile Network Prefix could
       be advertised in a Mobile Network.
    Prefix Table
       A list of Mobile Network Prefixes indexed by the Home Address
       of a Mobile Router.  The Home Agent manages and uses Prefix
       Table to determine which Mobile Network Prefixes belong to a
       particular Mobile Router.

3. Overview of the NEMO Protocol

 A Mobile Network is a network segment or subnet that can move and
 attach to arbitrary points in the routing infrastructure.  A Mobile
 Network can only be accessed via specific gateways called Mobile
 Routers that manage its movement.  Mobile Networks have at least one
 Mobile Router serving them.  A Mobile Router does not distribute the
 Mobile Network routes to the infrastructure at its point of
 attachment (i.e., in the visited network).  Instead, it maintains a
 bi-directional tunnel to a Home Agent that advertises an aggregation
 of Mobile Networks to the infrastructure.  The Mobile Router is also
 the default gateway for the Mobile Network.
 A Mobile Network can also comprise of multiple and nested subnets.  A
 router without mobility support may be permanently attached to a
 Mobile Network for local distribution.  Also, Mobile Routers may be
 attached to Mobile Networks owned by different Mobile Routers and may
 form a graph.  In particular, with Basic NEMO Support, each Mobile
 Router is attached to another Mobile Network by a single interface.
 If loops are avoided, the graph is a tree.
 A Mobile Router has a unique Home Address through which it is
 reachable when it is registered with its Home Agent.  The Home
 Address is configured from a prefix aggregated and advertised by its
 Home Agent.  The prefix could be either the prefix advertised on the
 home link or the prefix delegated to the Mobile Router.  The Mobile

Devarapalli, et al. Standards Track [Page 4] RFC 3963 NEMO Basic Support Protocol January 2005

 Router can have more than one Home Address if there are multiple
 prefixes in the home link.  The Mobile Router also advertises one or
 more prefixes in the Mobile Network attached to it.  The actual
 mechanism for assigning these prefixes to a given Mobile Router is
 outside the scope of this specification.
 When the Mobile Router moves away from the home link and attaches to
 a new access router, it acquires a Care-of Address from the visited
 link.  The Mobile Router can at any time act either as a Mobile Host
 or as a Mobile Router.  It acts as a Mobile Host as defined in [1]
 for sessions it originates and provides connectivity to the Mobile
 Network.  As soon as the Mobile Router acquires a Care-of Address, it
 immediately sends a Binding Update to its Home Agent as described in
 [1].  When the Home Agent receives this Binding Update, it creates a
 cache entry binding the Mobile Router's Home Address to its Care-of
 Address at the current point of attachment.
 If the Mobile Router seeks to act as a Mobile Router and provide
 connectivity to nodes in the Mobile Network, it indicates this to the
 Home Agent by setting a flag (R) in the Binding Update.  It MAY also
 include information about the Mobile Network Prefix in the Binding
 Update by using one of the modes described in section 5.2, so that
 the Home Agent can forward packets meant for nodes in the Mobile
 Network to the Mobile Router.  A new Mobility Header Option for
 carrying prefix information is described in section 4.3.  If the
 Mobile Network has more than one IPv6 prefix and wants the Home Agent
 to setup forwarding for all of these prefixes, it includes multiple
 prefix information options in a single Binding Update.  The Home
 Agent sets up forwarding for each of these prefixes to the Mobile
 Router's Care-of Address.  In some scenarios the Home Agent would
 already know which prefixes belong to a Mobile Router by an alternate
 mechanism such as static configuration.  In these scenarios, the
 Mobile Router does not include any prefix information in the Binding
 Update.  The Home Agent sets up forwarding for all prefixes owned by
 the Mobile Router when it receives a Binding Update from the Mobile
 Router with the Mobile Router Flag (R) set.
 The Home Agent acknowledges the Binding Update by sending a Binding
 Acknowledgement to the Mobile Router.  A positive acknowledgement
 with the Mobile Router Flag (R) set means that the Home Agent has set
 up forwarding for the Mobile Network.  Once the binding process
 finishes, a bi-directional tunnel is established between the Home
 Agent and the Mobile Router.  The tunnel end points are the Mobile
 Router's Care-of Address and the Home Agent's address.  If a packet
 with a source address belonging to the Mobile Network Prefix is
 received from the Mobile Network, the Mobile Router reverse-tunnels
 the packet to the Home Agent through this tunnel.  This reverse-
 tunneling is done by using IP-in-IP encapsulation [3].  The Home

Devarapalli, et al. Standards Track [Page 5] RFC 3963 NEMO Basic Support Protocol January 2005

 Agent decapsulates this packet and forwards it to the Correspondent
 Node.  For traffic originated by itself, the Mobile Router can use
 either reverse tunneling or route optimization, as specified in [1].
 When a Correspondent Node sends a data packet to a node in the Mobile
 Network, the packet is routed to the Home Agent that currently has
 the binding for the Mobile Router.  The Mobile Router's network
 prefix would be aggregated at the Home Agent, which would advertise
 the resulting aggregation.  Alternatively, the Home Agent may receive
 the data packets destined to the Mobile Network by advertising routes
 to the Mobile Network Prefix.  The actual mechanism by which these
 routes are advertised is outside the scope of this document.  When
 the Home Agent receives a data packet meant for a node in the Mobile
 Network, it tunnels the packet to the Mobile Router's current Care-of
 Address.  The Mobile Router decapsulates the packet and forwards it
 onto the interface where the Mobile Network is connected.  Before
 decapsulating the tunneled packet, the Mobile Router has to check
 whether the Source address on the outer IPv6 header is the Home
 Agent's address.  This check is not necessary if the packet is
 protected by IPsec in tunnel mode.  The Mobile Router also has to
 make sure that the destination address on the inner IPv6 header
 belongs to a prefix used in the Mobile Network before forwarding the
 packet to the Mobile Network.  If it does not, the Mobile Router
 should drop the packet.
 The Mobile Network could include nodes that do not support mobility
 and nodes that do.  A node in the Mobile Network can also be a fixed
 or a Mobile Router.  The protocol described here ensures complete
 transparency of network mobility to the nodes in the Mobile Network.
 Mobile Nodes that attach to the Mobile Network treat it as a normal
 IPv6 access network and run the Mobile IPv6 protocol.
 The Mobile Router and the Home Agent can run a routing protocol
 through the bi-directional tunnel.  In this case, the Mobile Router
 need not include prefix information in the Binding Update.  Instead,
 the Home Agent uses the routing protocol updates to set up forwarding
 for the Mobile Network.  When the routing protocol is running, the
 bi-directional tunnel must be treated as a tunnel interface.  The
 tunnel interface is included in the list of interfaces on which
 routing protocol is active.  The Mobile Router should be configured
 not to send any routing protocol messages on its egress interface
 when it is away from the home link and connected to a visited link.
 Finally, the Home Agent may be configured with static routes to the
 Mobile Network Prefix via the Mobile Router's Home Address.  In this
 case, the routes are set independently of the binding flows and the
 returning home of a Mobile Router.  The benefit is that such movement
 does not induce additional signalling in the form of routing updates

Devarapalli, et al. Standards Track [Page 6] RFC 3963 NEMO Basic Support Protocol January 2005

 in the home network.  The drawback is that the routes are present
 even if the related Mobile Routers are not reachable (at home or
 bound) at a given point of time.

4. Message Formats

4.1. Binding Update

 A new flag (R) is included in the Binding Update to indicate to the
 Home Agent whether the Binding Update is coming from a Mobile Router
 and not from a mobile node.  The rest of the Binding Update format
 remains the same as defined in [1].
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                 |          Sequence #           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |A|H|L|K|M|R|      Reserved     |           Lifetime            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Mobile Router Flag (R)
       The Mobile Router Flag is set to indicate to the Home Agent
       that the Binding Update is from a Mobile Router.  If the flag
       is set to 0, the Home Agent assumes that the Mobile Router is
       behaving as a Mobile Node, and it MUST NOT forward packets
       destined for the Mobile Network to the Mobile Router.
    Mobility Options
       A variable length field that can include zero or more mobility
       options.  This document defines a new mobility option in
       addition to what is defined in [1].
 For descriptions of the other fields in the message, see [1].

4.2. Binding Acknowledgement

 A new flag (R) is included in the Binding Acknowledgement to indicate
 that the Home Agent that processed the corresponding Binding Update
 supports Mobile Routers.  The flag is set only if the corresponding
 Binding Update had the Mobile Router Flag (R) set to 1.  The rest of
 the Binding Acknowledgement format remains the same, as defined in
 [1].

Devarapalli, et al. Standards Track [Page 7] RFC 3963 NEMO Basic Support Protocol January 2005

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                 |   Status      |K|R|  Reserved |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Sequence #            |           Lifetime            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Mobile Router Flag (R)
       The Mobile Router Flag is set to indicate that the Home Agent
       that processed the Binding Update supports Mobile Routers.  It
       is set to 1 only if the corresponding Binding Update had the
       Mobile Router Flag set to 1.
 For descriptions of the other fields in the message, see [1].
 This document also introduces the following new Binding
 Acknowledgement status values.  The values shown below are decimal
 values.
    140     Mobile Router Operation not permitted
    141     Invalid Prefix
    142     Not Authorized for Prefix
    143     Forwarding Setup failed (prefixes missing)
 Status values less than 128 indicate that the Binding Update was
 processed successfully by the receiving nodes.  Values greater than
 128 indicate that the Binding Update was rejected by the Home Agent.

4.3. Mobile Network Prefix Option

 The Mobile Network Prefix Option is included in the Binding Update to
 indicate the prefix information for the Mobile Network to the Home
 Agent.  There could be multiple Mobile Network Prefix Options if the
 Mobile Router has more than one IPv6 prefix in the Mobile Network and
 wants the Home Agent to forward packets for each of these prefixes to
 the Mobile Router's current location.
 The Mobile Network Prefix Option has an alignment requirement of
 8n+4.  Its format is as follows.

Devarapalli, et al. Standards Track [Page 8] RFC 3963 NEMO Basic Support Protocol January 2005

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      Type     |   Length      |   Reserved    | Prefix Length |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 +                                                               +
 |                                                               |
 +                   Mobile Network Prefix                       +
 |                                                               |
 +                                                               +
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Type
       6
    Length
       Eight-bit unsigned integer indicating the length in octets of
       the option, excluding the type and length fields.  Set to 18.
    Reserved
       This field is unused for now.  The value MUST be initialized to
       0 by the sender and MUST be ignored by the receiver.
    Prefix Length
       Eight-bit unsigned integer indicating the prefix length of the
       IPv6 prefix contained in the option.
    Mobile Network Prefix
       A sixteen-byte field containing the Mobile Network Prefix

5. Mobile Router Operation

 Mobile Router operation is derived largely from the combined
 behaviors of a host, of a router [5], and of a Mobile Node [1].
 A Mobile Node can act in two ways: (1) as a Mobile Host, in which
 case the Home Agent doesn't maintain any prefix information related
 to the Mobile Host's Home Address but does maintain a binding cache
 entry related to the Mobile Host's Home Address, and (2) as a Mobile
 Router, in which case, in addition to maintaining the binding cache
 entry corresponding to the Mobile Router Home Address, the Home Agent

Devarapalli, et al. Standards Track [Page 9] RFC 3963 NEMO Basic Support Protocol January 2005

 maintains forwarding information related to prefixes assigned to the
 Mobile Network.  The distinction between the two modes is represented
 by the value of the Mobile Router Flag (R).
 A Mobile Router MUST implement all requirements for IPv6 Mobile Nodes
 as described in section 8.5 of [1].

5.1. Data Structures

 Like a Mobile Host, a Mobile Router also maintains a Binding Update
 List, described in section 11.1 of the Mobile IPv6 specification [1].
 The Binding Update list is a conceptual data structure that records
 information sent in the Binding Updates.  There is one entry per each
 destination to which the Mobile Router is currently sending Binding
 Updates.
 This document introduces a new Prefix Information field in the
 Binding Update list structure.  This field is used to store any
 prefix information that the Mobile Router includes in the Binding
 Update.  If the Mobile Router sets the Mobile Router Flag (R) in the
 Binding Update but does not include any prefix information in it this
 field is set to null.  The Mobile Router does not include prefix
 information in the Binding Update in the implicit mode or when it,
 runs a dynamic routing protocol with its Home Agent.
 As does a Mobile Host, a Mobile Router stores the information
 regarding status of flags of the Binding Update in the corresponding
 Binding Update List entry.  This document introduces a new Mobile
 Router Flag (R) for this entry.  The status of this flag is stored in
 the Binding Update list whenever a Binding Update is sent.
 A Mobile Router also maintains a Home Agent list populated according
 to the same procedure as a Mobile Host.

5.2. Sending Binding Updates

 A Mobile Router sends Binding Updates to its Home Agent, as described
 in [1].  If the Mobile Router is not running a routing protocol as
 described in section 8, it uses one of the following modes to tell
 the Home Agent to determine which prefixes belong to the Mobile
 Router.  In both modes, the Mobile Router sets the Mobile Router Flag
 (R).
    Implicit:
       In this mode, the Mobile Router does not include a Mobile
       Network Prefix Option in the Binding Update.  The Home Agent
       can use any mechanism (not defined in this document) to

Devarapalli, et al. Standards Track [Page 10] RFC 3963 NEMO Basic Support Protocol January 2005

       determine the Mobile Network Prefix(es) owned by the Mobile
       Router and to set up forwarding for the Mobile Network.  One
       example would be manual configuration at the Home Agent mapping
       the Mobile Router's Home Address to the information required
       for setting up forwarding for the Mobile Network.
    Explicit:
       In this mode, the Mobile Router includes one or more Mobile
       Network Prefix Options in the Binding Update.  These options
       contain information about the Mobile Network Prefix(es)
       configured on the Mobile Network.
 A Mobile Router MUST implement at least one mode and MAY implement
 both.  In the latter case, local configuration on the Mobile Router
 decides which mode to use.  This is out of scope for this document.
 If the Mobile Router Flag is set, the Home Registration Flag (H) MUST
 be set.
 If the Mobile Router has a valid binding cache entry at the Home
 Agent, subsequent Binding Updates for the same Home Address should
 have the same value as the value in the binding cache for the Mobile
 Router Flag (R).  In explicit mode, the Mobile Router MUST include
 prefix information in all Binding Updates, including those sent to
 refresh existing binding cache entries, if it wants forwarding
 enabled for the corresponding Mobile Network Prefixes.

5.3. Receiving Binding Acknowledgements

 The Mobile Router receives Binding Acknowledgements from the Home
 Agent corresponding to the Binding Updates it sent.  If the Binding
 Acknowledgement status is set to 0 (Binding Update accepted) and the
 Mobile Router Flag (R) is set to 1, the Mobile Router assumes that
 the Home Agent has successfully processed the Binding Update and has
 set up forwarding for the Mobile Network.  The Mobile Router can then
 start using the bi-directional tunnel to reverse-tunnel traffic from
 the Mobile Network.  If the Mobile Router Flag (R) is not set, then
 the Mobile Router concludes that its current Home Agent does not
 support Mobile Routers and it performs Dynamic Home Agent Address
 Discovery again to discover Home Agents that do.  The Mobile Router
 MUST also de-register with the Home Agent that did not support it
 before attempting registration with another.

Devarapalli, et al. Standards Track [Page 11] RFC 3963 NEMO Basic Support Protocol January 2005

5.4. Error Processing

 If the Binding Acknowledgement status is set to a value between 128
 and 139, the Mobile Router takes necessary actions as described in
 the Mobile IPv6 specification [1].  For the Binding Acknowledgement
 status values defined in this document, the following sections
 explain the Mobile Router's behavior.

5.4.1. Implicit Mode

 In Implicit mode, the Mobile Router interprets only error statuses
 140 (Mobile Router Operation not permitted) and 143 (Forwarding Setup
 failed).  The Mobile Router MUST treat Binding Acknowledgements with
 statuses '141' and '142' as fatal errors, since they should not be
 sent by the Home Agent in implicit mode.
 If the Binding Acknowledgement from the Home Agent has the status
 140, the Mobile Router SHOULD send a Binding Update to another Home
 Agent on the same home link.  If no Home Agent replies positively,
 the Mobile Router MUST refrain from sending Binding Updates with the
 Mobile Router Flag set to any Home Agent on the home link, and it
 must log the information.
 If the Binding Acknowledgement has the status 143, the Mobile Router
 SHOULD send a Binding Update to another Home Agent on the same home
 link.  If no Home Agent replies positively, the Mobile Router SHOULD
 refrain from sending this Binding Update to any Home Agent on the
 home link, and MAY send Binding Updates in Explicit mode to a Home
 Agent on the same home link.

5.4.2. Explicit Mode

 If the Mobile Router sent a Binding Update to the Home Agent in
 explicit mode, then the Mobile Router interprets only error statuses
 140 (Mobile Router Operation not permitted), 141 (Invalid Prefix),
 and 142 (Not Authorized for Prefix).  The Mobile Router MUST treat
 Binding Acknowledgements with status '143' as a fatal error, since it
 should not be sent by the Home Agent in explicit mode.
 If the Binding Acknowledgement from the Home Agent has the status
 140, the Mobile Router SHOULD send a Binding Update to another Home
 Agent on the same home link.  If no Home Agent replies positively,
 then the Mobile Router MUST refrain from sending Binding Updates with
 the Mobile Router Flag set to any Home Agent on the home link, and it
 must log the information.
 If the Binding Acknowledgement has the status 141 or 142, the Mobile
 Router SHOULD send a Binding Update to another Home Agent on the same

Devarapalli, et al. Standards Track [Page 12] RFC 3963 NEMO Basic Support Protocol January 2005

 home link.  If no Home Agent replies positively, then the Mobile
 Router SHOULD refrain from sending Binding Updates to any Home Agent
 on the home link.  The Mobile Router MUST also stop advertising the
 prefix in the Mobile Network and try to obtain new IPv6 prefix
 information for the Mobile Network.  It would do this by the same
 means that it initially got assigned the current Mobile Network
 Prefix.  Alternatively, the Mobile Router MAY send Binding Updates in
 Implicit mode to a Home Agent on the same home link.
 If by the end of this Error Processing procedure, as described in
 sections 5.4.1 and 5.4.2, the Mobile Router has tried every available
 mode and still has not received a positive Binding Acknowledgement,
 the Mobile Router MUST stop sending Binding Updates with the Mobile
 Router Flag set for this Home Address and it must log the
 information.
 In all cases above, the Mobile Router MUST conclude that the Home
 Agent did not create a binding cache entry for the Mobile Router's
 Home Address.

5.5. Establishment of Bi-directional Tunnel

 When a successful Binding Acknowledgement is received, the Mobile
 Router sets up its endpoint of the bi-directional tunnel.
 The bi-directional tunnel between the Mobile Router and the Home
 Agent allows packets to flow in both directions, while the Mobile
 Router is connected to a visited link.  The bi-directional tunnel is
 created by merging two unidirectional tunnels, as described in RFC
 2473 [3].  The tunnel from the Mobile Router to the Home Agent has
 the Care-of address of the Mobile Router as the tunnel entry point
 and the Home Agent's address as the tunnel exit point.  The tunnel
 from the Home Agent to the Mobile Router has the Home Agent's address
 and the Mobile Router's Care-of Address as the tunnel entry point and
 exit point, respectively.  All IPv6 traffic to and from the Mobile
 Network is sent through this bi-directional tunnel.
 A Mobile Router uses the Tunnel Hop Limit normally assigned to
 routers (not to hosts).  Please refer to [3] for more details.

5.6. Neighbor Discovery for Mobile Router

 When the Mobile Router is at home, it MAY be configured to send
 Router Advertisements and to reply to Router Solicitations on the
 interface attached to the home link.  The value of the Router
 Lifetime field SHOULD be set to 0 to prevent other nodes from
 configuring the Mobile Router as the default router.

Devarapalli, et al. Standards Track [Page 13] RFC 3963 NEMO Basic Support Protocol January 2005

 A Mobile Router SHOULD NOT send unsolicited Router Advertisements and
 SHOULD NOT reply to Router Solicitations on any egress interface when
 that interface is attached to a visited link.  However, the Mobile
 Router SHOULD reply with Neighbor Advertisements to Neighbor
 Solicitations received on the egress interface, for addresses valid
 on the visited link.
 A router typically ignores Router Advertisements sent by other
 routers on a link.  However, a Mobile Router MUST NOT ignore Router
 Advertisements received on the egress interface.  The received Router
 Advertisements MAY be used for address configuration, default router
 selection, or movement detection.

5.7. Multicast Groups for Mobile Router

 When at home, the Mobile Router joins the multicast group All Routers
 Address with scopes 1 interface-local (on the home-advertising
 interface), and 2 link-local, on any of its egress interfaces.  When
 in a visited network, the Mobile Router MUST NOT join the above
 multicast groups on the corresponding interface.

5.8. Returning Home

 When the Mobile Router detects that it has returned to its home link,
 it MUST de-register with its Home Agent.  The Mobile Router MUST
 implement and follow the returning-home procedures defined for a
 mobile node in [1].  In addition, the Mobile Router MAY start
 behaving as a router on its egress interface, especially as follows:
  1. The Mobile Router MAY send Router Advertisements on its egress

interfaces, but the router lifetime SHOULD be set to 0 so that

    hosts on the home link do not pick the Mobile Router as the
    default router.
  1. The Mobile Router MAY join the All Routers Address multicast group

on the home link.

  1. The Mobile Router MAY send routing protocol messages on its egress

interface if it is configured to run a dynamic routing protocol.

 When the Mobile Router sends a de-registration Binding Update in
 Explicit mode, it SHOULD NOT include any Mobile Network Prefix
 options in the Binding Update.  When the Home Agent removes a binding
 cache entry, it deletes all associated Mobile Network Prefix routes.

Devarapalli, et al. Standards Track [Page 14] RFC 3963 NEMO Basic Support Protocol January 2005

6. Home Agent Operation

 For a Mobile Router to operate correctly, the Home Agent MUST satisfy
 all the requirements listed in section 8.4 of [1].  The Home Agent
 MUST implement both modes described in section 5.2 of this document.

6.1. Data Structures

6.1.1. Binding Cache

 The Home Agent maintains Binding Cache Entries for each Mobile Router
 currently registered with the Home Agent.  The Binding Cache is a
 conceptual data structure described in detail in [1].
 The Home Agent might need to store the Mobile Network Prefixes
 associated with a Mobile Router in the corresponding Binding Cache
 Entry.  This is required if the Binding Update that created the
 Binding Cache Entry contained explicit prefix information.  This
 information can be used later to clean up routes installed in
 explicit mode, when the Binding Cache Entry is removed, and to
 maintain the routing table, for instance, should the routes be
 removed manually.
 The Home Agent also stores the status of the Mobile Router Flag (R)
 in the Binding Cache entry.

6.1.2. Prefix Table

 The Home Agent SHOULD be able to prevent a Mobile Router from
 claiming Mobile Network Prefixes belonging to another Mobile Router.
 The Home Agent can prevent such attacks if it maintains a Prefix
 Table and verifies the prefix information provided by the Mobile
 Router against Prefix Table entries.  The Prefix Table SHOULD be used
 by the Home Agent when it processes a Binding Update in explicit
 mode.  It is not required when a dynamic routing protocol is run
 between the Mobile Router and the Home Agent.
 Each entry in the Prefix Table contains the following fields:
  1. The Home Address of the Mobile Router. This field is used as the

key for searching the pre-configured Prefix Table.

  1. The Mobile Network Prefix of the Mobile Router associated with the

Home Address.

Devarapalli, et al. Standards Track [Page 15] RFC 3963 NEMO Basic Support Protocol January 2005

6.2. Mobile Network Prefix Registration

 The Home Agent processes the Binding Update as described in section
 10.3.1 of the Mobile IPv6 specification [1].  This section describes
 the processing of the Binding Update if the Mobile Router (R) Flag is
 set.  The Home Agent performs the following check.
  1. The Home Registration (H) Flag MUST be set. If it is not, the

Home Agent MUST reject the Binding Update and send a Binding

    Acknowledgement with status set to 140.  Note: The basic support
    does not allow sending a Binding Update for a Mobile Network
    Prefix to correspondent nodes (for route optimization).
  1. Mobile IPv6 specification [1] requires that the Home Address in

the Binding Update be configured from a prefix advertised on the

    home link.  Otherwise the Binding Update is rejected with status
    value 132 [1].  This specification relaxes this requirement so
    that the Home Agent rejects the Binding Update only if the Home
    Address does not belong to the prefix that the Home Agent is
    configured to serve.
 If the Home Agent has a valid binding cache entry for the Mobile
 Router, and if the Binding Update has the Mobile Router Flag (R) set
 to a value different from that in the existing binding cache entry,
 then the Home Agent MUST reject the Binding Update and send a Binding
 Acknowledgement with status set to 139 (Registration type change
 disallowed).  However, if the Binding Update is a de-registration
 Binding Update, the Home Agent ignores the value of the Mobile Router
 Flag (R).
 If the Lifetime specified in the Binding Update is 0 or the specified
 Care-of address matches the Home Address in the Binding Update, then
 this is a request to delete the cached binding for the home address
 and specified Mobile Network Prefixes.  The Binding Update is
 processed as described in section 6.7.
 If the Home Agent does not reject the Binding Update as invalid, and
 if a dynamic routing protocol is not run between the Home Agent and
 the Mobile Router as described in section 8, then the Home Agent
 retrieves the Mobile Network Prefix information as described below.
  1. If a Mobile Network Prefix Option is present in the Binding

Update, the prefix information for the Mobile Network Prefix is

    retrieved from the Mobile Network Prefix field and the Prefix
    Length field of the option.  If the Binding Update contains more
    than one option, the Home Agent MUST set up forwarding for all the
    Mobile Network Prefixes.  If the Home Agent fails to set up
    forwarding to all the prefixes listed in the Binding Update, then

Devarapalli, et al. Standards Track [Page 16] RFC 3963 NEMO Basic Support Protocol January 2005

    it MUST NOT forward traffic to any of the prefixes.  Furthermore,
    it MUST reject the Binding Update and send a Binding
    Acknowledgement with status set to 141 (Invalid Prefix).
    If the Home Agent verifies the prefix information with the Prefix
    Table and the check fails, the Home Agent MUST discard the Binding
    Update and send a Binding Acknowledgement with status set to 142
    (Not Authorized for Prefix).
  1. If there is no option in the Binding Update carrying prefix

information, the Home Agent uses manual pre-configured information

    to determine the prefixes assigned to the Mobile Router and to set
    up forwarding for the Mobile Network.  If there is no information
    that the Home Agent can use, it MUST reject the Binding Update and
    send a Binding Acknowledgement with status set to 143 (Forwarding
    Setup failed).
 If the Home Agent has a valid binding cache entry for the Mobile
 Router, it should compare the list of prefixes in the Binding Update
 against the prefixes stored in the binding cache entry.  If the
 binding cache entry contains prefixes that do not appear in the
 Binding Update, the Home Agent MUST disable forwarding for these
 Mobile Network Prefixes.
 If all checks are passed, the Home Agent creates a binding cache
 entry for Mobile Router's Home Address or updates the entry if it
 already exists.  Otherwise, the Home Agent MUST NOT register the
 binding of the Mobile Router's Home Address.
 The Home Agent defends the Mobile Router's Home Address through Proxy
 Neighbor Discovery by multicasting a Neighbor Advertisement message
 onto the home link on behalf of the Mobile Router.  All fields in the
 Proxy Neighbor Advertisement message should be set the same way they
 would be by the Mobile Router if it sent this Neighbor Advertisement
 while at home, as described in [6].  There is an exception:  If the
 Mobile Router (R) Flag has been set in the Binding Update, the Router
 (R) bit in the Advertisement MUST be set.
 The Home Agent also creates a bi-directional tunnel to the Mobile
 Router for the requested Mobile Network Prefix or updates an existing
 bi-directional tunnel as described in section 6.4.

6.3. Advertising Mobile Network Reachability

 To receive packets meant for the Mobile Network, the Home Agent
 advertises reachability to the Mobile Network.  If the Home Link is
 configured with an aggregated prefix and the Mobile Network Prefix is
 aggregated under that prefix, then the routing changes related to the

Devarapalli, et al. Standards Track [Page 17] RFC 3963 NEMO Basic Support Protocol January 2005

 Mobile Network may be restricted to the Home Link.  If the Home Agent
 is the only default router on the Home Link, routes to the Mobile
 Network Prefix are aggregated naturally under the Home Agent, which
 does not have to do anything special.
 If the Home Agent receives routing updates through a dynamic routing
 protocol from the Mobile Router, it can be configured to propagate
 those routes on the relevant interfaces.

6.4. Establishment of Bi-directional Tunnel

 The implementation of the bi-directional tunnels and the mechanism
 for attaching them to the IP stack are outside the scope of this
 specification.  However, all implementations MUST be capable of the
 following operations:
  1. The Home Agent can tunnel packets meant for the Mobile Network

prefix to the Mobile Router's current location, the Care-of

    Address.
  1. The Home Agent can accept packets tunneled by the Mobile Router

with the source address of the outer IPv6 header set to the Mobile

    Router's Care-of Address.

6.5. Forwarding Packets

 When the Home Agent receives a data packet destined for the Mobile
 Network, it MUST forward the packet to the Mobile Router through the
 bi-directional tunnel.  The Home Agent uses either the routing table,
 the Binding Cache, or a combination to route packets to the Mobile
 Network.  This is implementation specific.  Two examples are shown
 below.
 1. The Home Agent maintains a route to the Mobile Network Prefix with
    the next hop set to the Mobile Router's Home Address.  When the
    Home Agent tries to forward the packet to the next hop, it finds a
    binding cache entry for the home address.  Then the Home Agent
    extracts the Mobile Router's Care-of address and tunnels the
    packet to the Care-of address.
 2. The Home Agent maintains a route to the Mobile Network Prefix with
    the outgoing interface set to the bi-directional tunnel interface
    between the Home Agent and the Mobile Router.  For this purpose,
    the Home Agent MUST treat this tunnel as a tunnel interface.  When
    the packets are forwarded through the tunnel interface, they are
    encapsulated automatically, with the source address and

Devarapalli, et al. Standards Track [Page 18] RFC 3963 NEMO Basic Support Protocol January 2005

    destination address in the outer IPv6 header set to the Home
    Agent's address and the Mobile Router's Care-of address,
    respectively.

6.6. Sending Binding Acknowledgements

 A Home Agent serving a Mobile Router sends Binding Acknowledgements
 with the same rules it uses for sending Binding Acknowledgements to
 Mobile Hosts [1], with the following enhancements.
 The Home Agent sets the status code in the Binding Acknowledgement to
 0 (Binding Update accepted) to indicate to the Mobile Router that it
 successfully processed the Binding Update.  It also sets the Mobile
 Router Flag (R) to indicate to the Mobile Router that it has set up
 forwarding for the Mobile Network.
 If the Home Agent is not configured to support Mobile Routers, it
 sets the status code in the Binding Acknowledgement to 140 (Mobile
 Router Operation not permitted).
 If one or more prefixes received in the Binding Update are invalid
 and the Home Agent cannot set up forwarding for the prefixes, the
 Home Agent sets the status code in the Binding Acknowledgement to 141
 (Invalid Prefix) to indicate this to the Mobile Router.
 If the Mobile Router is not authorized to use this Home Address to
 forward packets for one or more prefixes present in the Binding
 Update, the Home Agent sets the status code in the Binding
 Acknowledgement to 142 (Not Authorized for Prefix) to indicate this.
 The Home Agent sets the status code to 143 (Forwarding Setup failed)
 if it is unable to determine the information needed to set up
 forwarding for the Mobile Network.  This is used in the Implicit
 mode, in which the Mobile Router does not include any prefix
 information in the Binding Update.

6.7. Mobile Network Prefix De-registration

 When the Home Agent successfully processes the de-registration BU, it
 deletes the Binding Cache Entry for the Mobile Router's Home Address
 and stops proxying the Home Address.  This is described in detail in
 the Mobile IPv6 specification [1].
 In addition, the Home Agent removes the bi-directional tunnel and
 stops forwarding packets to the Mobile Network.  The Home Agent
 should keep all necessary information to clean up whichever routes it
 installed, whether they come from an implicit or explicit source.

Devarapalli, et al. Standards Track [Page 19] RFC 3963 NEMO Basic Support Protocol January 2005

 In Explicit mode, the Home Agent MUST ignore any Mobile Network
 Prefix Options present in the de-registration Binding Update.

7. Modifications to Dynamic Home Agent Address Discovery

 This document extends the Dynamic Home Agent Address Discovery
 (DHAAD) defined in [1] so that Mobile Routers only attempt
 registration with Home Agents that support them.

7.1. Modified Dynamic Home Agent Discovery Address Request

 A new flag (R) (Support for Mobile Routers) is introduced in the
 DHAAD Request message, defined in [1].  The Mobile Router sets this
 flag to indicate that it wants to discover Home Agents supporting
 Mobile Routers.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |     Code      |            Checksum           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Identifier           |R|          Reserved           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Mobile Router Support Flag (R)
       A one-bit flag that when set indicates that the Mobile Router
       wants to discover Home Agents supporting Mobile Routers.
    For a description of the other fields in the message, see [1].

7.2. Modified Dynamic Home Agent Discovery Address Request

 A new flag (R) (Support for Mobile Routers) is introduced in the
 DHAAD Reply message, defined in [1].  If a Home Agent receives a
 Dynamic Home Agent Discovery request message with the Mobile Router
 Support Flag set, it MUST reply with a list of Home Agents supporting
 Mobile Routers.  The Mobile Router Support Flag MUST be set if there
 is at least one Home Agent supporting Mobile Routers.  If none of the
 Home Agents support Mobile Routers, the Home Agent MAY reply with a
 list of Home Agents that only support Mobile IPv6 Mobile Nodes.  In
 this case, the Mobile Router Support Flag MUST be set to 0.

Devarapalli, et al. Standards Track [Page 20] RFC 3963 NEMO Basic Support Protocol January 2005

 The modified message format is as follows.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |     Code      |            Checksum           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Identifier          |R|           Reserved          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 +                                                               +
 +                                                               +
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Mobile Router Support Flag (R)
       A one-bit flag that when set indicates that the Home Agents
       listed in this message support Mobile Routers.
    For a description of the other fields in the message, see [1].

7.3. Modified Home Agent Information Option

 A new flag (R) (Support for Mobile Routers) is introduced in the Home
 Agent Information Option defined in [1].  If a Home Agent supports
 Mobile Routers, it SHOULD set the flag.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |    Length     |R|         Reserved            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Home Agent Preference     |      Home Agent Lifetime      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Mobile Router Support Flag (R)
       A one-bit flag that when set indicates that the Home Agent
       supports Mobile Routers.
    For a description of the other fields in the message, see [1].

Devarapalli, et al. Standards Track [Page 21] RFC 3963 NEMO Basic Support Protocol January 2005

8. Support for Dynamic Routing Protocols

 In the solution described so far, forwarding to the Mobile Network at
 the Home Agent is set up when the Home Agent receives a Binding
 Update from the Mobile Router.  An alternative to this is for the
 Home Agent and the Mobile Router to run an intra-domain routing
 protocol such as RIPng [12] and OSPF [13] through the bi-directional
 tunnel.  The Mobile Router can continue running the same routing
 protocol that it ran when attached to the home link.
 Support for running a intra-domain routing protocol is optional and
 is governed by the configuration on the Mobile Router and the Home
 Agent.
 This feature is very useful when the Mobile Network is large with
 multiple subnets containing different IPv6 prefixes.  Routing changes
 in the Mobile Network are quickly propagated to the Home Agent.
 Routing changes in the home link are quickly propagated to the Mobile
 Router.
 When the Mobile Router is attached to the home link, it runs a
 routing protocol by sending routing updates through its egress
 interface.  When the Mobile Router moves and attaches to a visited
 network, it should stop sending routing updates on the interface by
 which it attaches to the visited link.  This reduces the chances that
 prefixes specific to the Mobile Network will be leaked to the visited
 network if routing protocol authentication is not enabled in the
 visited network and in the Mobile Network.  It is expected that
 normal deployment practices will include proper authentication
 mechanisms to prevent unauthorized route announcements on both the
 home and visited networks.  The Mobile Router then starts sending
 routing protocol messages through the bi-directional tunnel toward
 the Home Agent.  Most routing protocols use link-local addresses as
 source addresses for the routing information messages.  The Mobile
 Router is allowed to use link-local addresses for the inner IPv6
 header of an encapsulated packet.  But these MUST NOT be forwarded to
 another link by either the Mobile Router or the Home Agent.
 When the Home Agent receives the inner packet, it processes the
 encapsulated routing protocol messages and updates its routing table
 accordingly.  As part of normal routing protocol operation, the next
 hop information in these routing entries is filled with the Mobile
 Router's link-local address, with the outgoing interface set to the
 bi-directional tunnel.
 Similarly, the Home Agent sends routing updates through the bi-
 directional tunnel to the Mobile Router.  The Mobile Router processes
 these routing protocol messages and updates its routing table.  For

Devarapalli, et al. Standards Track [Page 22] RFC 3963 NEMO Basic Support Protocol January 2005

 all routes advertised by the Home Agent, the Mobile Router sets the
 outgoing interface to the bi-directional tunnel to the Home Agent.
 When the Mobile Router and the Home Agent exchange routes through a
 dynamic routing protocol, the Mobile Router SHOULD NOT include Mobile
 Network Prefixes in the Binding Update to the Home Agent.  Depending
 on its configuration, the Home Agent might not add routes based on
 the prefix information in the Binding Updates and might use only the
 routing protocol updates.  Moreover, including prefix information in
 both the Binding Updates and the routing protocol updates is
 redundant.
 As the routing protocol messages from the Home Agent to the Mobile
 Router could potentially contain information about the internal
 routing structure of the home network, these messages require
 authentication and confidentiality protection.  Appropriate
 authentication and confidentiality protection mechanisms, defined in
 [14], MUST be used.  For protecting routing protocol messages by
 using IPsec ESP [4], the bi-directional tunnel between the Mobile
 Router and the Home Agent should be treated as the outgoing
 interface, with the Home Agent and Mobile Router's addresses as
 source and destination addresses for the inner encapsulated messages.
 If a link state routing protocol such as OSPFv3 is run by the Mobile
 Router and the Home Agent, the recommendations in Appendix B should
 be followed.

9. Security Considerations

 All signaling messages between the Mobile Router and the Home Agent
 MUST be authenticated by IPsec [8].  The use of IPsec to protect
 Mobile IPv6 signaling messages is described in detail in the HA-MN
 IPsec specification [2].  The signaling messages described in this
 document extend Mobile IPv6 messages and do not require any changes
 to what is described in [2].
 The Mobile Router has to perform ingress filtering on packets
 received from the Mobile Network to ensure that nodes in the Mobile
 Network do not use the bi-directional tunnel to launch IP spoofing
 attacks.  In particular, the Mobile Router SHOULD check that the IP
 source addresses in the packets received belong to the Mobile Network
 Prefix and are not the same as one of the addresses used by the
 Mobile Router.  If the Mobile Router receives an IP-in-IP tunneled
 packet from a node in the Mobile Network and it has to forward the
 decapsulated packet, it SHOULD perform the above mentioned checks on
 the source address of the inner packet.

Devarapalli, et al. Standards Track [Page 23] RFC 3963 NEMO Basic Support Protocol January 2005

 The Home Agent has to verify that packets received through the bi-
 directional tunnel belong to the Mobile Network.  This check is
 necessary to prevent nodes from using the Home Agent to launch
 attacks that would have otherwise been prevented by ingress
 filtering.  The source address of the outer IPv6 header MUST be set
 to the Mobile Router's current Care-of Address.  The source address
 of the inner IPv6 header MUST be topologically correct with respect
 to the IPv6 prefixes used in the Mobile Network.
 If the Mobile Router sends a Binding Update with a one or more Mobile
 Network Prefix options, the Home Agent MUST be able to verify that
 the Mobile Router is authorized for the prefixes before setting up
 forwarding for the prefixes.
 When the Mobile Router runs a dynamic routing protocol as described
 in section 8, it injects routing update messages into the Home Link.
 As the routing protocol message could contain information about the
 internal routing structure of the home network, these messages
 require confidentiality protection.  The Mobile Router SHOULD use
 confidentiality protection through IPsec ESP as described in [14].
 If the bi-directional tunnel between the Mobile Router and the Home
 Agent is protected by ESP, in tunnel mode for all IP traffic, then no
 additional confidentiality protection specific to the routing
 protocol is required.
 Home Agents and Mobile Routers may use IPsec ESP to protect payload
 packets tunneled between themselves.  This is useful to protect
 communications against attackers on the path of the tunnel.
 Please refer to the Mobile IPv6 specification [1] for security
 considerations when the Mobile Router operates as a Mobile Host.

10. IANA Considerations

 This document defines a new Mobility Header Option, the Mobile
 Network Prefix Option as described in section 4.3.  The type value
 for this option MUST be assigned from the same space used by the
 mobility options defined in [1].
 This document also defines the following new Binding Acknowledgement
 status values.  These status values are defined in section 4.2 and
 MUST be assigned from the same space used for Binding Acknowledgement
 status values in [1].
  1. Mobile Router Operation not permitted
  2. Invalid Prefix
  3. Not Authorized for Prefix
  4. Forwarding Setup failed (prefixes missing)

Devarapalli, et al. Standards Track [Page 24] RFC 3963 NEMO Basic Support Protocol January 2005

11. Contributors

 We would like to acknowledge Ludovic Bellier, Claude Castelluccia,
 Thierry Ernst [15], Miguel Catalina-Gallego, Christophe Janneteau,
 T.J.  Kniveton, Hong-Yon Lach, Jari T. Malinen, Koshiro Mitsuya,
 Alexis Olivereau, Charles E. Perkins, and Keisuke Uehara for their
 work on earlier proposals for Network Mobility.  This document has
 inherited a lot of ideas from these proposals.

12. Acknowledgements

 We thank all members of the NEMO Working Group, and of the preceding
 MONET BoF, for fruitful discussions on the mailing list and at IETF
 meetings.
 Kent Leung, Marco Molteni, and Patrick Wetterwald are acknowledged
 for their work on Network Mobility for IPv4 and IPv6.
 Tim Leinmueller is acknowledged for many insightful remarks and for
 section 7.
 Jari Arkko, James Kempf, Chan-Wah Ng, and Erik Nordmark are
 acknowledged for their thorough review and comments.
 Souhwan Jung, Fan Zhao, S. Felix Wu, HyunGon Kim, and SungWon Sohn
 are acknowledged for identifying threats related to tunneling between
 the Mobile Network and the Home Agent.

13. References

13.1. Normative References

 [1]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
      IPv6", RFC 3775, June 2004.
 [2]  Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to
      Protect Mobile IPv6 Signaling between Mobile Nodes and Home
      Agents", RFC 3776, June 2004.
 [3]  Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6
      Specification", RFC 2473, December 1998.
 [4]  Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
      (ESP)", RFC 2406, November 1998.
 [5]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
      Specification", RFC 2460, December 1998.

Devarapalli, et al. Standards Track [Page 25] RFC 3963 NEMO Basic Support Protocol January 2005

 [6]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
      for IP Version 6 (IPv6)", RFC 2461, December 1998.
 [7]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.

13.2. Informative References

 [8]  Kent, S. and R. Atkinson, "Security Architecture for the
      Internet Protocol", RFC 2401, November 1998.
 [9]  Manner, J. and M. Kojo, Eds., "Mobility Related Terminology",
      RFC 3753, June 2004.
 [10] Ernst, T., and H.-Y. Lach, "Network Mobility Support
      Terminology", Work in Progress, October 2004.
 [11] Ernst, T., "Network Mobility Support Goals and Requirements",
      Work in Progress, October 2004.
 [12] Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080, January
      1997.
 [13] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6", RFC 2740,
      December 1999.
 [14] Gupta, M. and N. Melam, "Authentication/Confidentiality for
      OSPFv3", Work in Progress, December 2004.
 [15] Ernst, T., "Network Mobility Support in IPv6", PhD Thesis,
      University Joseph Fourier, Grenoble, France. October 2001.
 [16] Moy, J., "Extending OSPF to Support Demand Circuits", RFC 1793,
      April 1995.
 [17] Thubert, P., et al., "NEMO Home Network models", Work in
      Progress, October 2004.

Devarapalli, et al. Standards Track [Page 26] RFC 3963 NEMO Basic Support Protocol January 2005

Appendix A. Examples of NEMO Basic Support Operation

 This section tries to illustrate the NEMO protocol by using a Mobile
 Router and a Mobile Node belonging to different administrative
 domains.  The Mobile Router's Mobile Network consists of a Local
 Fixed Node (LFN) and a Local Fixed Router (LFR) [10].  The LFR has an
 access link to which other Mobile Nodes or Mobile Routers could
 attach.
 Figure 1 depicts the scenario where both the Mobile Router and the
 Mobile Node are at home.
              +----+       +-------+
              | MN |       | HA_MN |
              +--+-+  1::  +---+---+
                2+-------------+3
                               |
                               |
 +-------+2 2:: +-------------------+ 3:: 2+-------+
 | CN_MN |------|     Internet      |------| CN_MR |
 +-------+      +-------------------+      +-------+
                      4::      |
                               |
                2+-------------+3
              +--+-+       +---+---+
              | MR |       | HA_MR |
              +--+-+       +-------+
             5:: |1
         ----------
         2|      |3
     +--+-+   +--+-+
     | LFN|   | LFR|
     +--+-+   +--+-+
             6:: |1
         ----------
 Figure 1.  Mobile Router and Mobile Node at home.

Devarapalli, et al. Standards Track [Page 27] RFC 3963 NEMO Basic Support Protocol January 2005

 The Mobile Router then moves away from the home link and attaches to
 a visited link.  This is shown in Figure 2.  The Mobile Router sends
 a Binding Update to HA_MR when it attaches to a visited link and
 configures a Care-of Address.  HA_MR creates a binding cache entry
 for the Mobile Router's Home Address and also sets up forwarding for
 the prefixes on the Mobile Network.
              +----+       +-------+
              | MN |       | HA_MN |
              +--+-+  1::  +---+---+
                2+-------------+3
                               |
                               |
 +-------+2 2:: +-------------------+ 3:: 2+-------+
 | CN_MN |------|     Internet      |------| CN_MR |
 +-------+      ++------------------+      +-------+
                 | 7::     4:: |           4::2->7::2
                 |             |
                2+             +3
              +--+-+       +---+---+
              | MR |       | HA_MR | 4::2->7::2
              +--+-+       +-------+ 5::/prefixlen -> forward
             5:: |1                                   to MR
         ----------                  6::/prefixlen -> forward
         2|      |3                                   to MR
     +--+-+   +--+-+
     | LFN|   | LFR|
     +--+-+   +--+-+
             6:: |1
         ----------
 Figure 2.  Mobile Router on a visited link.

Devarapalli, et al. Standards Track [Page 28] RFC 3963 NEMO Basic Support Protocol January 2005

 Figure 3 shows the Mobile Node moving away from its home link and
 attaching to the Mobile Router.  The Mobile Node configures a Care-of
 Address from the prefix advertised on the Mobile Network and sends a
 Binding Update to its Home Agent (HA_MN) and to its Correspondent
 Node (CN_MN).  Both HA_MN and CN_MN create binding cache entries for
 the Mobile Node's Home Address.
                            +-------+
                            | HA_MN | 1::2->6::2
                       1::  +---+---+
                       ---------|3
                                |
                                |
  +-------+2 2:: +-------------------+ 3:: 2+-------+
  | CN_MN |------|     Internet      |------| CN_MR |
  +-------+      ++------------------+      +-------+
 1::2->6::2       | 7::     4:: |           4::2->7::2
                  |             |
                 2+             +3
               +--+-+       +---+---+
               | MR |       | HA_MR | 4::2->7::2
               +--+-+       +-------+ 5::/prefixlen -> forward
              5:: |1                                   to MR
          ----------                  6::/prefixlen -> forward
          2|      |3                                   to MR
      +--+-+   +--+-+
      | LFN|   | LFR|
      +--+-+   +--+-+
              6:: |1
          --------+-
                  |2
               +--+-+
               | MN |
               +----+
     Figure 3.  Mobile Node attached to Mobile
                Router on a visited link

Devarapalli, et al. Standards Track [Page 29] RFC 3963 NEMO Basic Support Protocol January 2005

Appendix B. Running Link State Routing Protocol with NEMO Basic Support

 The bi-directional tunnel between the Mobile Router and the Home
 Agent is used as a virtual interface over which routing protocol
 messages are exchanged.  When a link state routing protocol is run,
 the following recommendations should be followed.

B.1. Tunnel Interface Considerations

 If the tunnel interface goes up and down every time the Mobile Router
 moves to a new visited network with a high level of mobility and a
 sufficient number of Mobile Routers, the amount of interface state
 changes will adversely affect the Home Agent's performance.  This
 also introduces a high level of instability in the home network.  To
 avoid this, the following should be considered when the bi-
 directional tunnel is implemented:
  1. A tunnel interface is consistently assigned to each Mobile Router,

as long as it has a valid binding cache at the Home Agent.

  1. Every time the Mobile Router moves and updates the binding cache

entry, the bi-directional tunnel should not be torn down and set

    up again.  The tunnel end points should be updated dynamically
    with the Mobile Router's current Care-of Address.
  1. With a large number of interfaces, Hello packet processing may

become a burden. Therefore, the tunnel interface should be

    treated as On-Demand circuits for OSPF [16].

B.2. OSPF Area Considerations

 The following should be considered when the Home Network is
 configured for running OSPF:
  1. The entire Home domain SHOULD NOT be configured as a single area

if a Home Agent supports Mobile Routers. At least the home

    network should be configured as a separate area.
  1. The bi-directional tunnel interfaces to the Mobile Routers should

never be included in the same area as the backbone links.

 For a more detailed discussion on configuring a home network for NEMO
 Basic Support, please see [17].

Devarapalli, et al. Standards Track [Page 30] RFC 3963 NEMO Basic Support Protocol January 2005

 One disadvantage of running OSPFv3 with NEMO Basic Support is the
 possibility that the Mobile Networks will be told of the topology of
 the entire home network, including all the fixed and Mobile Routers.
 The only thing the Mobile Routers might really need is a default
 route through the Home Agent.
 To reduce the amount of routing protocol messages received by a
 Mobile Router, one can configure each bi-directional tunnel to a
 Mobile Router as a separate area.  But this requires that the Home
 Agent support a large number of OSPF areas if it supports a large
 number of Mobile Routers, and it might not be possible with most
 router implementations.
 Another option is to configure multiple areas on the Home Link and
 group a number of Mobile Routers into each area.  This reduces the
 number of areas that a Home Agent needs to support but also reduces
 the amount of routing protocol traffic that a Mobile Router receives.

Devarapalli, et al. Standards Track [Page 31] RFC 3963 NEMO Basic Support Protocol January 2005

Authors' Addresses

 Vijay Devarapalli
 Nokia Research Center
 313 Fairchild Drive
 Mountain View, CA 94043
 USA
 EMail:  vijay.devarapalli@nokia.com
 Ryuji Wakikawa
 Keio University and WIDE
 5322 Endo Fujisawa Kanagawa
 252-8520
 Japan
 EMail:  ryuji@sfc.wide.ad.jp
 Alexandru Petrescu
 Motorola Labs
 Parc les Algorithmes Saint Aubin
 Gif-sur-Yvette 91193
 France
 EMail:  Alexandru.Petrescu@motorola.com
 Pascal Thubert
 Cisco Systems Technology Center
 Village d'Entreprises Green Side
 400, Avenue Roumanille
 Biot - Sophia Antipolis 06410
 France
 EMail:  pthubert@cisco.com

Devarapalli, et al. Standards Track [Page 32] RFC 3963 NEMO Basic Support Protocol January 2005

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Devarapalli, et al. Standards Track [Page 33]

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