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rfc:rfc5177

Network Working Group K. Leung Request for Comments: 5177 G. Dommety Category: Standards Track Cisco Systems

                                                          V. Narayanan
                                                        Qualcomm, Inc.
                                                           A. Petrescu
                                                              Motorola
                                                            April 2008
         Network Mobility (NEMO) Extensions for Mobile IPv4

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Abstract

 This document describes a protocol for supporting Mobile Networks
 between a Mobile Router and a Home Agent by extending the Mobile IPv4
 protocol.  A Mobile Router is responsible for the mobility of one or
 more network segments or subnets moving together.  The Mobile Router
 hides its mobility from the nodes on the Mobile Network.  The nodes
 on the Mobile Network may be fixed in relationship to the Mobile
 Router and may not have any mobility function.
 Extensions to Mobile IPv4 are introduced to support Mobile Networks.

Leung, et al. Standards Track [Page 1] RFC 5177 Mobile Router April 2008

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.1.  Examples of Mobile Networks  . . . . . . . . . . . . . . .  3
   1.2.  Overview of Protocol . . . . . . . . . . . . . . . . . . .  5
 2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
 3.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  7
 4.  Mobile Network Extensions  . . . . . . . . . . . . . . . . . .  8
   4.1.  Mobile Network Request Extension . . . . . . . . . . . . .  8
   4.2.  Mobile Network Acknowledgement Extension . . . . . . . . .  9
 5.  Mobile Router Operation  . . . . . . . . . . . . . . . . . . . 11
   5.1.  Error Processing . . . . . . . . . . . . . . . . . . . . . 12
   5.2.  Mobile Router Management . . . . . . . . . . . . . . . . . 12
 6.  Home Agent Operation . . . . . . . . . . . . . . . . . . . . . 13
   6.1.  Summary  . . . . . . . . . . . . . . . . . . . . . . . . . 13
   6.2.  Data Structures  . . . . . . . . . . . . . . . . . . . . . 14
     6.2.1.  Registration Table . . . . . . . . . . . . . . . . . . 14
     6.2.2.  Prefix Table . . . . . . . . . . . . . . . . . . . . . 14
   6.3.  Mobile Network Prefix Registration . . . . . . . . . . . . 14
   6.4.  Advertising Mobile Network Reachability  . . . . . . . . . 16
   6.5.  Establishment of Bi-directional Tunnel . . . . . . . . . . 16
   6.6.  Sending Registration Replies . . . . . . . . . . . . . . . 17
   6.7.  Mobile Network Prefix Deregistration . . . . . . . . . . . 17
 7.  Data Forwarding Operation  . . . . . . . . . . . . . . . . . . 17
 8.  Nested Mobile Networks . . . . . . . . . . . . . . . . . . . . 18
 9.  Routing Protocol between Mobile Router and Home Agent  . . . . 18
 10. Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   10.1. Security when Dynamic Routing Protocol Is Used . . . . . . 20
 11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
   13.1. Normative References . . . . . . . . . . . . . . . . . . . 23
   13.2. Informative References . . . . . . . . . . . . . . . . . . 24

Leung, et al. Standards Track [Page 2] RFC 5177 Mobile Router April 2008

1. Introduction

 This document describes network mobility extensions to the Mobile
 IPv4 protocol.  The goal of introducing these extensions is to
 accommodate mobility scenarios where groups of hosts and routers move
 homogeneously (as a whole).  It is required that all hosts and
 routers in a Mobile Network be able to run applications connecting to
 the Internet, and be reachable from the Internet.
 For details regarding terminology related to network mobility (NEMO),
 a quick read of RFC 4885 [RFC4885] is suggested.

1.1. Examples of Mobile Networks

 A Mobile Network links together a set of hosts and routers.
 Connecting this Mobile Network to the Internet is ensured at two
 levels: first, a Mobile Router is connected on one side to the Mobile
 Network and on another side to a wireless access system; second, a
 Home Agent placed on the home link manages traffic between the
 Correspondent Node and a Local Fixed Node (LFN, a node in the Mobile
 Network) by means of encapsulating traffic.
 A scenario of applicability for this Mobile Network is described
 next.  A Mobile Network is formed by a wireless-enabled Personal
 Digital Assistant (PDA) and a portable photographic camera, linked
 together by Bluetooth wireless link-layer technology.  This is
 sometimes referred to as a Personal Area Network (PAN).  In the
 illustration below, one can notice the PDA playing the role of a
 Mobile Router and the camera the role of Local Fixed Node.

Leung, et al. Standards Track [Page 3] RFC 5177 Mobile Router April 2008

| HA |

  1. — ——–

| / \ —-

  1. +——–| Internet |———| CN |

\ / —-

  1. ——-

/ \

                              /            \
                             /              \
                           ----            ----
                          | AR |          | AR |
                           ----            ----
                             |cellular       |cellular
                      /      |cellular
                      |    ----        ----
             Mobile   |   | MR |      |LFN |   ---movement-->
            Network   <    ----        ----
                      |      |           |
                      |     -+-----------+-
                      \       Bluetooth
 The camera (Local Fixed Node) uploads photographic content to a
 Correspondent Node (CN) server.  When the Mobile Network moves away,
 the Mobile Router serving the Mobile Network changes its point of
 attachment from one cellular access (Access Router) to another,
 obtaining a new Care-of Address.  The Home Agent (HA) encapsulates
 application traffic for the CN and LFN.
 Whereas the illustration above is a very simple instantiation of the
 applicability of Mobile IP-based Mobile Networks, more complex Mobile
 Networks are easily accommodated by the Mobile IPv4 extensions
 presented in this document (NEMOv4).  For example, laptop computers
 used by passengers in a bus, train, ship, or plane should all be
 considered as forming Mobile Networks, as long as they move together
 (homogeneously).

Leung, et al. Standards Track [Page 4] RFC 5177 Mobile Router April 2008

1.2. Overview of Protocol

 As introduced previously, this document presents extensions to the
 Mobile IPv4 protocol.  The entities sending and receiving these
 extensions are the Mobile Router and the Home Agent.  The Local Fixed
 Node is relieved from running Mobile IP software and, although it
 moves (together with the Mobile Network), its IP stack is not seeing
 any change in addressing.
 Mobility for the entire Mobile Network is supported by the Mobile
 Router registering its current point of attachment (Care-of Address)
 to its Home Agent: the Mobile Router sends an extended Registration
 Request to the Home Agent, which returns an extended Registration
 Reply.  This signaling sets up the tunnel between the two entities,
 as illustrated in the following figure:
                LFN        MR                      HA        CN
                 |         |                       |         |
                 |         | Extended Registration |         |
                 |         |---------------------->|         |
                 |         |        Request        |         |
                 |         |                       |         |
                 |         |                       |         |
                 |         | Extended Registration |         |
                 |         |<----------------------|         |
                 |         |        Reply          |         |
                 |         |                       |         |
                 |<--------o=======================o-------->|
                 |         |     Encapsulated      |         |
                 |         |  Application Traffic  |         |
                 |         |                       |         |
 The prefix(es) used within a Mobile Network (either implicitly
 configured on the Home Agent or explicitly identified by the Mobile
 Router in the Registration Request) is/are advertised by the Home
 Agent for route propagation in the home network.  Traffic to and from
 nodes in the Mobile Network are tunneled by the Home Agent to the
 Mobile Router, and vice versa.  Though packets from a Local Fixed
 Node placed in the Mobile Network can be forwarded by the Mobile
 Router directly without tunneling (if reverse tunneling were not
 used), these packets will be dropped if ingress filtering is turned
 on at the Access Router.
 Extensively relating to Mobile IPv4 [RFC3344], this specification
 addresses mainly the co-located Care-of Address mode.  Foreign Agent
 Care-of Address mode (with 'legacy' Foreign Agents [RFC3344]) is

Leung, et al. Standards Track [Page 5] RFC 5177 Mobile Router April 2008

 supported but without optimization, and with double encapsulation
 being used.  For an optimization of this mode, the gentle reader is
 directed to an extension document [NEMOv4-FA].
 Compared to Mobile IPv4, this document specifies an additional tunnel
 between a Mobile Router's Home Address and the Home Agent.  This
 tunnel is encapsulated within the normal tunnel between the Care-of
 Address (CoA) and Home Agent.  In Foreign Agent CoA mode, the tunnel
 between the Mobile Router and Home Agent is needed to allow the
 Foreign Agent to direct the decapsulated packet to the proper
 visiting Mobile Router.  However, in co-located CoA mode, the
 additional tunnel is not essential and could be eliminated because
 the Mobile Router is the recipient of the encapsulated packets for
 the Mobile Network; a proposal for this feature is in the extending
 document mentioned above [NEMOv4-FA].
 All traffic between the nodes in the Mobile Network and the
 Correspondent Nodes passes through the Home Agent.  This document
 does not touch on aspects related to route optimization of this
 traffic.
 A similar protocol has been documented in RFC 3963 [RFC3963] for
 supporting IPv6 Mobile Networks with Mobile IPv6 extensions.
 Multihoming for Mobile Routers is outside the scope of this document.

2. 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 [RFC2119].
 Terminology for Mobile IPv4 mobility support is defined in RFC 3344
 [RFC3344].  Terminology for network mobility support (NEMO), from an
 IPv6 perspective, is described in RFC 4885 [RFC4885].  In addition,
 this document defines the following terms for NEMOv4.
 Mobile Router
         RFC 3344 [RFC3344] defines a Mobile Router as a mobile node
         that can be a router that is responsible for the mobility of
         one or more entire networks moving together, perhaps on an
         airplane, a ship, a train, an automobile, a bicycle, or a
         kayak.

Leung, et al. Standards Track [Page 6] RFC 5177 Mobile Router April 2008

 Mobile Network Prefix
         The network prefix of the subnet delegated to a Mobile Router
         as the 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 the
         Prefix Table to determine which Mobile Network Prefixes
         belong to a particular Mobile Router.
 Local Fixed Node
         RFC 4885 [RFC4885] defines a Local Fixed Node (LFN) to be a
         fixed node belonging to the Mobile Network and unable to
         change its point of attachment.  This definition should not
         be confused with "Long, Fat Network, LFN" of RFC 1323
         [RFC1323], at least because the latter is pronounced
         "elephan(t)" whereas a NEMO LFN is distinctively pronounced
         "elefen".

3. Requirements

 Although the original Mobile IPv4 specifications stated that Mobile
 Networks can be supported by the Mobile Router and Home Agent using
 static configuration or running a routing protocol (see Section 4.5
 of RFC 3344 [RFC3344]), there is no solution for explicit
 registration of the Mobile Networks served by the Mobile Router.  A
 solution needs to provide the Home Agent a means to ensure that a
 Mobile Router claiming a certain Mobile Network Prefix is authorized
 to do so.  A solution would also expose the Mobile Network Prefixes
 (and potentially other subnet-relevant information) in the exchanged
 messages, to aid in network debugging.
 The following requirements for Mobile Network support are enumerated:
 o  A Mobile Router should be able to operate in explicit or implicit
    mode.  A Mobile Router may explicitly inform the Home Agent which
    Mobile Network(s) need to be propagated via a routing protocol.  A
    Mobile Router may also function in implicit mode, where the Home
    Agent may learn the Mobile Networks through other means, such as
    from the AAA server, via pre-configuration, or via a dynamic
    routing protocol.
 o  The Mobile Network should be supported using Foreign Agents that
    are compliant to RFC 3344 [RFC3344] without any changes ('legacy'
    Foreign Agents).

Leung, et al. Standards Track [Page 7] RFC 5177 Mobile Router April 2008

 o  The Mobile Network should allow Fixed Nodes, Mobile Nodes, or
    Mobile Routers to be on it.
 o  The Local Fixed Nodes on a Mobile Network should be able to
    execute their sessions without running Mobile IP stacks.  The
    Mobile Router managing the LFNs' Mobile Network is 'hiding'
    mobility events like the changes of the Care-of Address from the
    Local Fixed Nodes in that Mobile Network.

4. Mobile Network Extensions

4.1. Mobile Network Request Extension

 For Explicit Mode, the Mobile Router informs the Home Agent about the
 Mobile Network Prefixes during registration.  The Registration
 Request contains zero, one, or several Mobile Network Request
 extensions in addition to any other extensions defined by or in the
 context of RFC 3344 [RFC3344].  When several Mobile Networks need to
 be registered, each is included in a separate Mobile Network Request
 extension, with its own Type, Length, Sub-Type, Prefix Length, and
 Prefix.  A Mobile Network Request extension is encoded in Type-
 Length-Value (TLV) format and respects the following ordering:
    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     |   Sub-Type    | Prefix Length |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Prefix                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Type:
         148     Mobile Network Extension
 Length:
         Decimal 6.
 Sub-Type:
         0       (Mobile Network Request)

Leung, et al. Standards Track [Page 8] RFC 5177 Mobile Router April 2008

 Prefix Length:
                 8-bit unsigned integer indicating the number of
                 leftmost bits covering the network part of the
                 address contained in the Prefix field.
 Prefix:
         32-bit unsigned integer in network byte-order containing an
         IPv4 address whose leftmost Prefix Length bits make up the
         Mobile Network Prefix.

4.2. Mobile Network Acknowledgement Extension

 The Registration Reply contains zero, one or several Mobile Network
 Acknowledgement extensions in addition to any other extensions
 defined by or in the context of RFC 3344 [RFC3344].  For Implicit
 Mode, the Mobile Network Acknowledgement informs the Mobile Router
 the prefixes for which the Home Agent sets up forwarding with respect
 to this Mobile Router.  Policies such as permitting only traffic from
 these Mobile Networks to be tunneled to the Home Agent may be applied
 by the Mobile Router.  For Explicit Mode, when several Mobile
 Networks need to be acknowledged explicitly, each is included in a
 separate Mobile Network Acknowledgement extension, with its own Type,
 Sub-Type, Length, Prefix, and Prefix Length fields.  At least one
 Mobile Network Acknowledgement extension MUST be in a successful
 Registration Reply to indicate to the Mobile Router that the Mobile
 Network Request extension was processed, and therefore was not
 skipped by the Home Agent.
 A Registration Reply may contain any non-zero number of Explicit Mode
 and Implicit Mode Acknowledgements sub-types.  Both sub-types can be
 present in a single Registration Reply.  A Mobile Network
 Acknowledgement extension is encoded in Type-Length-Value (TLV)
 format.  When the registration is denied with Code HA_MOBNET_ERROR
 (Code field in the Registration Reply), the Code field in the
 included Mobile Network Extension provides the reason for the
 failure.
     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     |   Sub-Type    |      Code     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Prefix Length |    Reserved   |            Prefix...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                ...Prefix           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Leung, et al. Standards Track [Page 9] RFC 5177 Mobile Router April 2008

 Type:
         148     Mobile Network Extension
 Length:
         Decimal 8.
 Sub-Type:
         1       (Explicit Mode Acknowledgement)
         2       (Implicit Mode Acknowledgement)
 Code:
         Value indicating success or failure:
         0       Success
         1       Invalid prefix (MOBNET_INVALID_PREFIX_LEN)
         2       Mobile Router is not authorized for prefix
                 (MOBNET_UNAUTHORIZED)
         3       Forwarding setup failed (MOBNET_FWDING_SETUP_FAILED)
 Prefix Length:
                 8-bit unsigned integer indicating the number of
                 leftmost bits covering the network part of the
                 address contained in the Prefix field.
 Reserved:
            Sent as zero; ignored on reception.
 Prefix:
         32-bit unsigned integer in network byte-order containing an
         IPv4 address whose leftmost Prefix Length bits make up the
         Mobile Network Prefix.

Leung, et al. Standards Track [Page 10] RFC 5177 Mobile Router April 2008

5. Mobile Router Operation

 A Mobile Router's operation is generally derived from the behavior of
 a Mobile Node, as set in RFC 3344 [RFC3344].  In addition to
 maintaining mobility bindings for its Home Address, the Mobile
 Router, together with the Home Agent, maintains forwarding
 information for the Mobile Network Prefix(es) assigned to the Mobile
 Router.
 A Mobile Router SHOULD set the 'T' bit to 1 in all Registration
 Request messages it sends to indicate the need for reverse tunnels
 for all traffic.  Without reverse tunnels, all the traffic from the
 Mobile Network will be subject to ingress filtering in the visited
 networks.  Upon reception of a successful Registration Reply, the
 Mobile Router processes the registration in accordance to RFC 3344
 [RFC3344].  In addition, the following steps are taken:
 o  Check for Mobile Network Acknowledgement extension(s) in
    Registration Reply.
 o  Create tunnel to the Home Agent if the Mobile Router is registered
    in reverse tunneling mode.
 o  Set up default route via this tunnel or egress interface when the
    Mobile Router is registered with or without reverse tunneling,
    respectively.
 In accordance with this specification, a Mobile Router may operate in
 one of the following two modes: explicit and implicit.  In explicit
 mode, the Mobile Router includes Mobile Network Prefix information in
 all Registration Requests (as Mobile Network Request extensions),
 while in implicit mode it does not include this information in any
 Registration Request.  In the latter case, the Home Agent obtains the
 Mobile Network Prefixes by other means than Mobile IP.  One example
 of obtaining the Mobile Network Prefix is through static
 configuration on the Home Agent.
 A Mobile Router can obtain a co-located or Foreign Agent Care-of
 Address while operating in explicit or implicit modes.
 For deregistration, the Mobile Router sends a registration request
 with lifetime set to zero without any Mobile Network Request
 extensions.

Leung, et al. Standards Track [Page 11] RFC 5177 Mobile Router April 2008

5.1. Error Processing

 In a Mobile IP Registration Reply message, there may be two Code
 fields: one proper to the Registration Reply header (the 'proper'
 Code) and one within the Mobile Network Acknowledgement Extension
 (simply the 'Code').  A Mobile Router interprets the values of the
 Code field in the Mobile Network Acknowledgement Extension of the
 Registration Reply in order to identify any error related to managing
 the Mobile Network Prefixes by the Home Agent.  It also interprets
 the values of the Code field in the Registration Reply header (the
 proper Code).
 If the value of the Code field in the Registration Reply (the proper)
 is set to HA_MOBNET_DISALLOWED, then the Mobile Router MUST stop
 sending Registration Requests with any Mobile Network Prefix
 extensions to that Home Agent.
 If the value of the Code field in the Registration Reply (the proper)
 is set to HA_MOBNET_ERROR, then the Mobile Router MUST stop sending
 Registration Requests that contain any of the Mobile Network Prefixes
 that are defined by the values of the fields Prefix and Prefix Length
 in the Mobile Network Acknowledgement extension.  Note that the
 registration is denied in this case, and no forwarding for any Mobile
 Network Prefixes would be set up by the Home Agent for the Mobile
 Router.
 It is possible that the Mobile Router receives a Registration Reply
 with no Mobile Network extensions if the registration was processed
 by a Mobile IPv4 Home Agent that does not support this specification
 at all.  In that case, the absence of Mobile Network extensions must
 be interpreted by the Mobile Router as the case where the Home Agent
 does not support Mobile Networks.
 All the error code values have been assigned by IANA; see Section 11.

5.2. Mobile Router Management

 Operating a Mobile Router in a Mobile IPv4 environment has certain
 requirements on the management of the necessary initial configuration
 and supervision of the ongoing status information.  Mobile Router
 maintenance indicators may need to be exposed in a manner consistent
 with other Mobile IPv4 indicators.
 The objects for the Management Information Base (MIB) for Mobile IPv4
 are defined in RFC 2006 [RFC2006].  The structure of the basic model
 of Mobile IP protocol describes three entities: Mobile Node, Home
 Agent, and Foreign Agent.  In addition to these entities, this
 document proposes a functional entity to be the Mobile Router.

Leung, et al. Standards Track [Page 12] RFC 5177 Mobile Router April 2008

 The necessary initial configuration at a NEMOv4-enabled Home Agent
 includes, but is not limited to, the contents of the Prefix Table.
 The Mobile Router MAY need to store the Mobile Network Prefixes as
 the initial configuration.
 The definition of MIB objects related to the Mobile Router and to a
 NEMOv4-enabled Home Agent is outside the scope of this document.

6. Home Agent Operation

6.1. Summary

 A Home Agent MUST support all the operations specified in RFC 3344
 [RFC3344] for Mobile Node support.  The Home Agent MUST support both
 implicit and explicit modes of operation for a Mobile Router.
 The Home Agent processes the registration in accordance to RFC 3344
 [RFC3344], which includes route setup to the Mobile Router's Home
 Address via the tunnel to the Care-of Address.  In addition, for a
 Mobile Router registering in explicit mode, the following steps are
 taken:
 1.  Check that the Mobile Network Prefix information is valid.
 2.  Ensure the Mobile Network Prefix(es) is/are authorized to be on
     the Mobile Router.
 3.  Create a tunnel to the Mobile Router if it does not already
     exist.
 4.  Set up route for the Mobile Network Prefix via this tunnel.
 5.  Propagate Mobile Network Prefix routes via routing protocol if
     necessary.
 6.  Send the Registration Reply with the Mobile Network
     Acknowledgement extension(s).
 If there are any subnet routes via the tunnel to the Mobile Router
 that are not specified in the Mobile Network extensions, these routes
 are removed.
 In the case where the Mobile Node is not permitted to act as a Mobile
 Router, the Home Agent sends a Registration Reply message whose Code
 field is HA_MOBNET_DISALLOWED (the proper Code field of the
 Registration Reply).

Leung, et al. Standards Track [Page 13] RFC 5177 Mobile Router April 2008

 For a Mobile Router registering in implicit mode, the Home Agent
 performs steps 3-6 above, once the registration request is processed
 successfully.
 For deregistration, the Home Agent removes the tunnel to the Mobile
 Router and all routes using this tunnel.  The Mobile Network
 extensions are ignored.

6.2. Data Structures

6.2.1. Registration Table

 The Registration Table in the Home Agent, in accordance with RFC 3344
 [RFC3344], contains binding information for every Mobile Node
 registered with it.  RFC 3344 [RFC3344] defines the format of a
 Registration Table.  In addition to all the parameters specified by
 RFC 3344 [RFC3344], the Home Agent MUST store the Mobile Network
 Prefixes associated with the Mobile Router in the corresponding
 registration entry, when the corresponding registration was performed
 in explicit mode.  When the Home Agent is advertising reachability to
 Mobile Network Prefixes served by a Mobile Router, the information
 stored in the Registration Table can be used.

6.2.2. Prefix Table

 The Home Agent must be able to authorize a Mobile Router for use of
 Mobile Network Prefixes when the Mobile Router is operating in
 explicit mode.  Also, when the Mobile Router operates in implicit
 mode, the Home Agent must be able to locate the Mobile Network
 Prefixes associated with that Mobile Router.  The Home Agent may
 store the Home Address of the Mobile Router along with the Mobile
 Network prefixes associated with that Mobile Router.  If the Mobile
 Router does not have a Home Address assigned, this table may store
 the Network Access Identifier (NAI) [RFC2794] of the Mobile Router
 that will be used in dynamic Home Address assignment.

6.3. Mobile Network Prefix Registration

 The Home Agent must process Registration Requests coming from Mobile
 Routers in accordance with this section.  RFC 3344 [RFC3344]
 specifies that the Home Address of a mobile node registering with a
 Home Agent must belong to a prefix advertised on the home network.
 In accordance with this specification, however, the Home Address must
 be configured from a prefix that is served by the Home Agent, not
 necessarily the one on the home network.

Leung, et al. Standards Track [Page 14] RFC 5177 Mobile Router April 2008

 If the Registration Request is valid, the Home Agent checks to see if
 there are any Mobile Network Prefix extensions included in the
 Registration Request.
 If so, the Mobile Network Prefix information is obtained from the
 included extensions, and the Home Address from the Home Address field
 of the Registration Request.  For every Mobile Network Prefix
 extension included in the registration request, the Home Agent MUST
 perform a check against the Prefix Table.  If the Prefix Table does
 not contain at least one entry pairing that Home Address to that
 Mobile Network Prefix, then the check fails; otherwise, it succeeds.
 Following this check against the Prefix Table, the Home Agent MUST
 construct a Registration Reply containing Mobile Network
 Acknowledgement extensions.  For a Mobile Network Prefix for which
 the check was unsuccessful, the Code field in the corresponding
 Mobile Network Acknowledgement extension should be set to
 MOBNET_UNAUTHORIZED.
 For a Mobile Network Prefix for which the check was successful, the
 Code field in the respective Mobile Network Acknowledgement
 extensions should be set to 0.
 The Home Agent MUST attempt to set up forwarding for each Mobile
 Network Prefix extension for which the Prefix Table check was
 successful.  If the forwarding setup fails for a particular Mobile
 Network Prefix (for reasons such as not enough memory available or
 not enough devices available), the Code field in the respective
 Mobile Network Acknowledgement extension should be set to
 MOBNET_FWDING_SETUP_FAILED.
 If forwarding and setup was successful for at least one Mobile
 Network Prefix, then the Code field (the proper) of the Registration
 Reply message should be set to 0.  Otherwise, when forwarding and
 setup was unsuccessful for each and every Mobile Network Prefixes,
 that Code (the proper) should be HA_MOBNET_ERROR.
 If the Registration Request is sent in implicit mode, i.e., without
 any Mobile Network Request extension, the Home Agent may use pre-
 configured Mobile Network prefix information for the Mobile Router to
 set up forwarding.
 If the Home Agent is updating an existing binding entry for the
 Mobile Router, it MUST check all the prefixes in the Registration
 Table against the prefixes included in the Registration Request.  If
 one or more Mobile Network prefixes are missing from the included

Leung, et al. Standards Track [Page 15] RFC 5177 Mobile Router April 2008

 information in the registration request, the Home Agent MUST delete
 those prefixes from the registration table.  Also, the Home Agent
 MUST disable forwarding for those prefixes.
 If all checks are successful, the Home Agent either creates a new
 entry for the Mobile Router or updates an existing binding entry for
 it and returns a successful registration reply back to the Mobile
 Router or the Foreign Agent (if the Registration Request was received
 from a Foreign Agent).
 In accordance with RFC 3344 [RFC3344], the Home Agent does proxy
 Address Resolution Protocol (ARP) for the Mobile Router Home Address
 when the Mobile Router Home Address is derived from the home network.
 If the 'T' bit is set, the Home Agent creates a bi-directional tunnel
 for the corresponding Mobile Network prefixes or updates the existing
 bi-directional tunnel.  This tunnel is maintained independent of the
 reverse tunnel for the Mobile Router home address itself.

6.4. Advertising Mobile Network Reachability

 If the Mobile Network prefixes served by the Home Agent are
 aggregated with the home network prefix and if the Home Agent is the
 default router on the home network, the Home Agent does not have to
 advertise the Mobile Network Prefixes.  The routes for the Mobile
 Network Prefix are automatically aggregated into the home network
 prefix (it is assumed that the Mobile Network Prefixes are
 automatically aggregated into the home network prefix).  If the
 Mobile Router updates the Mobile Network prefix routes via a dynamic
 routing protocol, the Home Agent SHOULD propagate the routes on the
 appropriate networks.

6.5. Establishment of Bi-directional Tunnel

 The Home Agent creates and maintains a bi-directional tunnel for the
 Mobile Network prefixes of a Mobile Router registered with it.  A
 Home Agent supporting IPv4 Mobile Router operation MUST be able to
 forward packets destined to the Mobile Network prefixes served by the
 Mobile Router to its Care-of Address.  Also, the Home Agent MUST be
 able to accept packets tunneled by the Mobile Router with the source
 address of the outer header set to the Care-of Address of the Mobile
 Router and that of the inner header set to the Mobile Router's Home
 Address or an address from one of the registered Mobile Network
 prefixes.

Leung, et al. Standards Track [Page 16] RFC 5177 Mobile Router April 2008

6.6. Sending Registration Replies

 The Home Agent MUST set the status code in the registration reply to
 0 to indicate successful processing of the Registration Request and
 successful setup of forwarding for at least one Mobile Network prefix
 served by the Mobile Router.  The Registration Reply MUST contain at
 least one Mobile Network Acknowledgement extension.
 If the Home Agent is unable to set up forwarding for one or more
 Mobile Network prefixes served by the Mobile Router, it MUST set the
 Mobile Network Acknowledgement Extension status Code in the
 Registration Reply to MOBNET_FWDING_SETUP_FAILED.  When the prefix
 length is zero or greater than decimal 32, the status Code MUST be
 set to MOBNET_INVALID_PREFIX_LEN.
 If the Mobile Router is not authorized to forward packets to a Mobile
 Network prefix included in the request, the Home Agent MUST set the
 Code to MOBNET_UNAUTHORIZED.

6.7. Mobile Network Prefix Deregistration

 If the received Registration Request is for deregistration of the
 Care-of Address, the Home Agent, upon successful processing of it,
 MUST delete the entry (or entries) from its Registration Table.  The
 Home Agent tears down the bi-directional tunnel and stops forwarding
 any packets to/from the Mobile Router.  The Home Agent MUST ignore
 any included Mobile Network Request extension in a deregistration
 request.

7. Data Forwarding Operation

 For traffic to the nodes in the Mobile Network, the Home Agent MUST
 perform double tunneling of the packet, if the Mobile Router had
 registered with a Foreign Agent Care-of Address.  In this case, the
 Home Agent MUST encapsulate the packet with the tunnel header (source
 IP address set to Home Agent, and destination IP address set to
 Mobile Router's Home Address) and then encapsulate one more time with
 the tunnel header (source IP address set to Home Agent, and
 destination IP address set to CoA).
 For optimization, the Home Agent SHOULD only encapsulate the packet
 with the tunnel header (source IP address set to Home Agent, and
 destination IP address set to CoA) for co-located CoA mode.
 When a Home Agent receives a packet from the Mobile Network prefix in
 the bi-directional tunnel, it MUST de-encapsulate the packet and
 route it as a normal IP packet.  It MUST verify that the incoming

Leung, et al. Standards Track [Page 17] RFC 5177 Mobile Router April 2008

 packet has the source IP address set to the Care-of Address of the
 Mobile Router.  The packet MUST be dropped if the source address is
 not set to the Care-of Address of the Mobile Router.
 For traffic from the nodes in the Mobile Network, the Mobile Router
 encapsulates the packet with a tunnel header (source IP address set
 to Mobile Router's Home Address, and destination IP address set to
 Home Agent) if reverse tunnel is enabled.  Otherwise, the packet is
 routed directly to the Foreign Agent or access router.
 In co-located CoA mode, the Mobile Router MAY encapsulate one more
 time with a tunnel header (source IP address set to the CoA and
 destination IP address set to Home Agent).

8. Nested Mobile Networks

 Nested Network Mobility is 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.  Two issues should be noted though.
 First, whenever physical loops occur in a nested aggregation of
 Mobile Networks, this protocol neither detects nor solves them --
 datagram forwarding may be blocked.  Second, Mobile Routers in a deep
 nested aggregation of Mobile Networks might introduce significant
 overhead on the data packets as each level of nesting introduces
 another tunnel header encapsulation.  Applications that do not
 support MTU discovery are adversely affected by the additional header
 encapsulations because the usable MTU is reduced with each level of
 nesting.

9. Routing Protocol between Mobile Router and Home Agent

 There are several benefits of running a dynamic routing protocol
 between the Mobile Router and the Home Agent.  If the Mobile Network
 is relatively large, including several wireless subnets, then the
 topology changes within the moving network can be exposed from the
 Mobile Router to the Home Agent by using a dynamic routing protocol.
 The purpose of the NEMOv4 protocol extensions to Mobile IPv4, as
 defined in previous sections, is not to inform the Home Agent about
 these topology changes, but to manage the mobility of the Mobile
 Router.
 Similarly, topology changes in the home network can be exposed to the
 Mobile Router by using a dynamic routing protocol.  This may be
 necessary when new fixed networks are added in the home network.

Leung, et al. Standards Track [Page 18] RFC 5177 Mobile Router April 2008

 Here too, the purpose of NEMOv4 extensions is not to inform the
 Mobile Router about topology changes at home.
 Examples of dynamic routing protocols include, but are not limited
 to, OSPF Version 2 [RFC2328], BGP [RFC4271], and RIP [RFC2453].
 The recommendations are related to how the routing protocol and the
 Mobile IPv4 implementation work in tandem on the Mobile Router and on
 the Home Agent (1) without creating incoherent states in the
 forwarding information bases at home and on the Mobile Router, (2)
 without introducing topologically incorrect addressing information in
 the visited domain, and (3) without duplicating sent data or over-
 provisioning security.
 The information exchanged between the Mobile Router and the Home
 Agent is sent over the bi-directional tunnel established by the
 Mobile IPv4 exchange Registration Request - Registration Reply (see
 Section 6.5).  If a network address and prefix of a subnet in the
 moving network is sent by the Mobile Router within a routing protocol
 message, then they SHOULD NOT be sent in the Mobile IPv4 Registration
 Request too.  This avoids incoherencies in the forwarding information
 bases.  The Mobile Router SHOULD use NEMOv4 implicit mode in this
 case (see Section 3).
 The Mobile Router SHOULD NOT send routing protocol information
 updates in the foreign network.  The subnet addresses and prefixes
 valid in the moving network are topologically incorrect in the
 visited network.
 If the Mobile Router and the Home Agent use a dynamic routing
 protocol over the tunnel interface, and if that protocol offers
 security mechanisms to protect that protocol's messages, then the
 security recommendations in Section 10.1 apply.

10. Security Considerations

 The Mobile Network extension is protected by the same rules as for
 Mobile IP extensions in registration messages.  See the Security
 Considerations section in RFC 3344 [RFC3344].
 The Home Agent MUST be able to verify that the Mobile Router is
 authorized to provide mobility service for the Mobile Networks in the
 Registration Request, before anchoring these Mobile Network Prefixes
 on behalf of the Mobile Router.  Forwarding for prefixes MUST NOT be
 set up without successful authorization of the Mobile Router for
 those prefixes.  The Mobile Router MUST be notified when there is a
 registration failure because it cannot be successfully authorized for
 prefixes it requested.

Leung, et al. Standards Track [Page 19] RFC 5177 Mobile Router April 2008

 All Registration Requests and replies MUST be authenticated by the
 MN-HA Authentication Extension as specified in RFC 3344 [RFC3344].
 When the registration request is sent in explicit mode, i.e., with
 one or more Mobile Network Prefix extensions, all the Mobile Network
 Prefix extensions MUST be included before the MN-HA Authentication
 extension.  Also, these extensions MUST be included in the
 calculation of the MN-HA authenticator value.
 The Mobile Router should perform ingress filtering on all the packets
 received on the Mobile Network prior to reverse tunneling them to the
 Home Agent.  The Mobile Router MUST drop any packets that do not have
 a source address belonging to the Mobile Network.
 The Mobile Router MUST also ensure that the source address of packets
 arriving on the Mobile Network is not the same as the Mobile Router's
 IP address on any interface.  These checks will protect against nodes
 attempting to launch IP spoofing attacks through the bi-directional
 tunnel.
 The Home Agent, upon receiving packets through the bi-directional
 tunnel, MUST verify that the source addresses of the outer IP header
 of the packets are set to the Mobile Router's Care-of Address.  Also,
 it MUST ensure that the source address of the inner IP header is a
 topologically correct address on the Mobile Network.  This will
 prevent nodes from using the Home Agent to launch attacks inside the
 protected network.

10.1. Security when Dynamic Routing Protocol Is Used

 If a dynamic routing protocol is used between the Mobile Router and
 the Home Agent to propagate the Mobile Network information into the
 home network, the routing updates SHOULD be protected with IPsec ESP
 confidentiality between the Mobile Router and Home Agent, to prevent
 information about home network topology from being visible to
 eavesdroppers.

11. IANA Considerations

 IANA has assigned rules for the existing registry "Mobile IPv4
 numbers - per RFC 3344".  The numbering space for Extensions that may
 appear in Mobile IP control messages (those sent to and from UDP port
 number 434) should be modified.

Leung, et al. Standards Track [Page 20] RFC 5177 Mobile Router April 2008

 The new Values and Names for the Type for Extensions appearing in
 Mobile IP control messages are the following:
                 +-------+--------------------------+
                 | Value | Name                     |
                 +-------+--------------------------+
                 |   148 | Mobile Network Extension |
                 +-------+--------------------------+
   Table 1: New Values and Names for Extensions in Mobile IP Control
                               Messages
 A new number space has been created for the Values and Names for the
 Sub-Type for Mobile Network Extensions.  This number space is
 initially defined to hold the following entries, allocated by this
 document:
          +-------+-----------------------------------------+
          | Value | Name                                    |
          +-------+-----------------------------------------+
          |     0 | Mobile Network Request Extension        |
          |     1 | Explicit Mode Acknowledgement Extension |
          |     2 | Implicit Mode Acknowledgement Extension |
          +-------+-----------------------------------------+
   Table 2: New Values and Names for the Sub-Type for Mobile Network
                              Extensions
 The policy of future assignments to this number space is following
 Standards Action or IESG Approval (see [RFC2434]).
 The new Code Values for Mobile IP Registration Reply messages are the
 following (for a registration denied by the Home Agent):
 +-------+-----------------------------------------------------------+
 | Value | Name                                                      |
 +-------+-----------------------------------------------------------+
 |   147 | Mobile Network Prefix operation error (HA_MOBNET_ERROR)   |
 |   148 | Mobile Router operation is not permitted                  |
 |       | (HA_MOBNET_DISALLOWED)                                    |
 +-------+-----------------------------------------------------------+
       Table 3: New Code Values for Mobile IP Registration Reply

Leung, et al. Standards Track [Page 21] RFC 5177 Mobile Router April 2008

 A new number space has been created for the Code Values for the
 Mobile Network Acknowledgement Extension.  This number space is
 initially defined to hold the following entries, allocated by this
 document (result of registration, as sent by the Home Agent):
 +---+---------------------------------------------------------------+
 | 0 | Success                                                       |
 | 1 | Invalid prefix length (MOBNET_INVALID_PREFIX_LEN)             |
 | 2 | Mobile Router is not authorized for prefix                    |
 |   | (MOBNET_UNAUTHORIZED)                                         |
 | 3 | Forwarding setup failed (MOBNET_FWDING_SETUP_FAILED)          |
 +---+---------------------------------------------------------------+
 Table 4: New Code Values for Mobile Network Acknowledgement Extension
 The policy of future assignments to this number space is following
 Standards Action or IESG Approval (see [RFC2434]).

12. Acknowledgements

 The authors would like to thank Christophe Janneteau, George
 Popovich, Ty Bekiares, Ganesh Srinivasan, Alpesh Patel, Ryuji
 Wakikawa, George Tsirtsis, and Henrik Levkowetz for their helpful
 discussions, reviews, and comments.  Vijay Devarapalli extensively
 reviewed one of the later versions of the document.  Hans Sjostrand
 identified the last clarifications with respect to Foreign Agent mode
 treatment.  Pete McCann contributed necessary refinements of many
 statements.
 Mobile IPv4 versions as early as 1996 (RFC 2002 by Charles Perkins)
 described Mobile Networks and Mobile Routers support.
 Fred Templin indicated the potential confusion for the term "LFN".
 Amanda Baber of IANA agreed on the principles of allocating numbers
 for this specification and suggested improvements on the IANA
 section.
 Tim Polk of the IESG identified a deeply entrenched error on managing
 the Code fields.
 Lars Eggert of the IESG suggested the accommodation of the otherwise
 legal non-contiguous netmask fields, instead of simply prefix
 lengths.
 Dan Romascanu of the IESG indicated the necessity of manageability of
 Mobile Routers and NEMOv4-enabled Home Agents and their deployability
 in MIP4 environments.

Leung, et al. Standards Track [Page 22] RFC 5177 Mobile Router April 2008

 David Borman of TSV-DIR reviewed this document as part of the
 transport area directorate's ongoing effort to review key IETF
 documents.  The implications of the growth of usable MTU adversely
 affecting applications deep in a Mobile Network were suggested.
 Gonzalo Camarillo provided a generalist review by an additional set
 of eyes for documents as they are being considered for publication
 (General Area Review Team).
 Jari Arkko of the IESG reviewed, suggested necessary improvements to,
 and diligently shepherded this document through IESG.

13. References

13.1. Normative References

 [RFC1323]    Jacobson, V., Braden, B., and D. Borman, "TCP Extensions
              for High Performance", RFC 1323, May 1992.
 [RFC2006]    Cong, D., Hamlen, M., and C. Perkins, "The Definitions
              of Managed Objects for IP Mobility Support using SMIv2",
              RFC 2006, October 1996.
 [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2328]    Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
 [RFC2434]    Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.
 [RFC2453]    Malkin, G., "RIP Version 2", STD 56, RFC 2453,
              November 1998.
 [RFC2794]    Calhoun, P. and C. Perkins, "Mobile IP Network Access
              Identifier Extension for IPv4", RFC 2794, March 2000.
 [RFC3344]    Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
              August 2002.
 [RFC4271]    Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

Leung, et al. Standards Track [Page 23] RFC 5177 Mobile Router April 2008

13.2. Informative References

 [NEMOv4-FA]  Tsirtsis, G., Park, V., Narayanan, V., and K. Leung, "FA
              extensions to NEMOv4 Base", Work in Progress,
              February 2008.
 [RFC3963]    Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
              Thubert, "Network Mobility (NEMO) Basic Support
              Protocol", RFC 3963, January 2005.
 [RFC4885]    Ernst, T. and H-Y. Lach, "Network Mobility Support
              Terminology", RFC 4885, July 2007.

Leung, et al. Standards Track [Page 24] RFC 5177 Mobile Router April 2008

Authors' Addresses

 Kent Leung
 Cisco Systems
 170 W. Tasman Drive
 San Jose, CA  95134
 USA
 Phone: +1 408-526-5030
 EMail: kleung@cisco.com
 Gopal Dommety
 Cisco Systems
 170 W. Tasman Drive
 San Jose, CA  95134
 USA
 Phone: +1 408-525-1404
 EMail: gdommety@cisco.com
 Vidya Narayanan
 QUALCOMM, Inc.
 5775 Morehouse Dr
 San Diego, CA
 USA
 Phone: +1 858-845-2483
 EMail: vidyan@qualcomm.com
 Alexandru Petrescu
 Motorola
 Parc les Algorithmes Saint Aubin
 Gif-sur-Yvette, Essonne  91140
 France
 Phone: +33 169354827
 EMail: alexandru.petrescu@motorola.com

Leung, et al. Standards Track [Page 25] RFC 5177 Mobile Router April 2008

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 contained in BCP 78, and except as set forth therein, the authors
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Leung, et al. Standards Track [Page 26]

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