Network Mobility (NEMO) Extensions for Mobile IPv4
draft-ietf-mip4-nemo-v4-base-07.txt

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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.

Table of Contents

1.  Introduction
2.  Terminology
3.  Requirements
4.  Mobile Network Extensions
    4.1.  Mobile Network Request Extension
    4.2.  Mobile Network Acknowledgement Extension
5.  Mobile Router Operation
    5.1.  Error Processing
6.  Home Agent Operation
    6.1.  Summary
    6.2.  Data Structures
        6.2.1.  Registration Table
        6.2.2.  Prefix Table
    6.3.  Mobile Network Prefix Registration
    6.4.  Advertising Mobile Network Reachability
    6.5.  Establishment of Bi-directional Tunnel
    6.6.  Sending Registration Replies
    6.7.  Mobile Network Prefix De-registration
7.  Data Forwarding Operation
8.  Nested Mobile Networks
9.  Routing Protocol between Mobile Router and Home Agent
10.  Security Considerations
    10.1.  Security when Dynamic Routing Protocol is Used
11.  IANA Considerations
12.  Acknowledgements
13.  References
    13.1.  Normative References
    13.2.  Informative References
Appendix A.  ChangeLog
§  Authors' Addresses
§  Intellectual Property and Copyright Statements

1.  Introduction

This document describes protocol extensions to Mobile IPv4 as per RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] and its update (Perkins, C., “IP Mobility Support for IPv4, revised,” April 2010.) [I‑D.ietf‑mip4‑rfc3344bis], to enable support for Mobile Networks. This draft addresses mainly the co-located Care-of Address mode. Foreign Agent Care-of Address mode (with 'legacy' Foreign Agents, RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344]) are supported but without optimization, double encapsulation being used. For an optimization of this mode, the gentle reader is directed to an extension document (Tsirtsis, G., Park, V., Narayanan, V., and K. Leung, “FA extensions to NEMOv4 Base,” April 2008.) [I‑D.ietf‑mip4‑nemov4‑fa].

A Mobile Network is defined as a network segment or subnet that can change its point of attachment to the routing infrastructure. Such movement is performed by a Mobile Router, which is the mobility entity that provides connectivity and reachability as well as session continuity for all the nodes in the Mobile Network. The Mobile Router typically serves as the default gateway for the hosts on the Mobile Network.

Mobility for the Mobile Network is supported by the Mobile Router registering the point of attachment to its Home Agent. This signaling sets up the tunnel between the two entities.

The Mobile Networks (either implicitly configured on the Home Agent or explicitly identified by the Mobile Router) are advertised by the Home Agent for route propagation. 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 the Mobile Network can be forwarded directly without tunneling (if reverse tunneling is not used) packets will be dropped if ingress filtering is turned on.

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 Collocated 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 an extension document (Tsirtsis, G., Park, V., Narayanan, V., and K. Leung, “FA extensions to NEMOv4 Base,” April 2008.) [I‑D.ietf‑mip4‑nemov4‑fa].

All traffic between the nodes in the Mobile Network and Correspondent Nodes passes through the Home Agent. This document does not cover route optimization of this traffic.

A similar protocol has been documented in RFC 3963 (Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert, “Network Mobility (NEMO) Basic Support Protocol,” January 2005.) [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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].

Terminology for network mobility support is defined in RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] and its update (Perkins, C., “IP Mobility Support for IPv4, revised,” April 2010.) [I‑D.ietf‑mip4‑rfc3344bis]. In addition, this document defines the following terms.

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 Prefix Table to determine which Mobile Network Prefixes belong to a particular Mobile Router.

3.  Requirements

Although Mobile IPv4 stated that Mobile Network can be supported by the Mobile Router and Home Agent using static configuration or running a routing protocol, 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:

• 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.
• The Mobile Network should be supported using Foreign Agents that are compliant to RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] without any changes ('legacy' Foreign Agents).
• The mobile network should allow Fixed Nodes, Mobile Nodes, or Mobile Routers to be on it.

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 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344]. When several Mobile Networks are needed to be registered, each is included in a separate Mobile Network Request extension, with its own Type, Length, Sub-Type, Prefix Length and Prefix fields. A Mobile Network Request extension is encoded in Type-Length-Value (TLV) format and respects the following format:

   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:

Mobile Network Extension (skippable type range to be assigned by IANA).

Length:

6

Sub-Type:

TBA

(Mobile Network Request)

Prefix Length:

8-bit unsigned integer indicating the number of 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 first 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 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] and its update (Perkins, C., “IP Mobility Support for IPv4, revised,” April 2010.) [I‑D.ietf‑mip4‑rfc3344bis]. 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 are needed to be acknowledged explicitly, each is included in a separate Mobile Network Acknowledgement extension, with its own Type, Sub-Type, Length and Prefix Length fields. Optionally, all requested Mobile Networks could be acknowledged using only one Mobile Network Acknowledgement extension with "Prefix Length" and "Prefix" fields set to zero. 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, thereby 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, the Code field in the 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type:

TBA

Mobile Network Extension (skippable type range to be assigned by IANA).

Length:

8

Sub-Type:

TBA

(Explicit Mode Acknowledgement)

TBA

(Implicit Mode Acknowledgement)

Code:

Value indicating success or failure:

TBA

Success

TBA

Invalid prefix (MOBNET_INVALID_PREFIX_LEN)

TBA

Mobile Router is not authorized for prefix (MOBNET_UNAUTHORIZED)

TBA

Forwarding setup failed (MOBNET_FWDING_SETUP_FAILED)

Prefix Length:

8-bit unsigned integer indicating the number of 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 first Prefix Length bits make up the Mobile Network Prefix.

5.  Mobile Router Operation

A Mobile Router's operation is generally derived from the behavior of a Mobile Node, as set in RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] and its update (Perkins, C., “IP Mobility Support for IPv4, revised,” April 2010.) [I‑D.ietf‑mip4‑rfc3344bis]. 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 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344]. In addition, the following steps are taken:

• Check for Mobile Network Acknowledgement extension(s) in Registration Reply
• Create tunnel to the Home Agent if registered in reverse tunneling mode
• Set up default route via this tunnel or egress interface when 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 this 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 Collocated or Foreign Agent Care-of Address while operating in explicit or implicit modes.

For de-registration, the Mobile Router sends a registration request with lifetime set to zero without any Mobile Network Request extensions.

5.1.  Error Processing

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.

If the value of the Code field in the Registration Reply 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 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 are TBA (To Be Assigned) subject to IANA allocation.

6.  Home Agent Operation

6.1.  Summary

A Home Agent MUST support all the operations specified in RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] and its update (Perkins, C., “IP Mobility Support for IPv4, revised,” April 2010.) [I‑D.ietf‑mip4‑rfc3344bis] 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 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344], which includes route set up 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 or are authorized to be on the Mobile Router
3. Create 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
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 denied message with error code HA_MOBNET_DISALLOWED.

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 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] and its update (Perkins, C., “IP Mobility Support for IPv4, revised,” April 2010.) [I‑D.ietf‑mip4‑rfc3344bis], contains binding information for every Mobile Node registered with it. RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] and its update (Perkins, C., “IP Mobility Support for IPv4, revised,” April 2010.) [I‑D.ietf‑mip4‑rfc3344bis] define the format of a Registration Table. In addition to all the parameters specified by RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] and its update (Perkins, C., “IP Mobility Support for IPv4, revised,” April 2010.) [I‑D.ietf‑mip4‑rfc3344bis], 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 NAI RFC 2794 (Calhoun, P. and C. Perkins, “Mobile IP Network Access Identifier Extension for IPv4,” March 2000.) [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. The document RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] and its update (Perkins, C., “IP Mobility Support for IPv4, revised,” April 2010.) [I‑D.ietf‑mip4‑rfc3344bis] specify 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.

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 unsuccessfull 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 successfull 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 successfull. If the forwarding setup fails for a particular Mobile Network Prefix (for reasons like not enough memory available, or not enough devices available, or other similar) 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 of the Registration Reply message should be set to 0. Otherwise that Code 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 prefix is missing from the included information in the registration request, it 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 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344], the Home Agent does proxy 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.

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 set up of forwarding for all the mobile network prefixes 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 of 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 32, the status code MUST be set to MOBNET_INVALID_PREFIX_LEN.

If the Mobile Router is not authorized to forward packets to one or mobile network prefixes included in the request, the Home Agent MUST set the code to MOBNET_UNAUTHORIZED_MR.

6.7.  Mobile Network Prefix De-registration

If the received registration request is for de-registration of the Care-of Address, the Home Agent, upon successful processing of it, MUST delete the entry(ies) 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 de-registration 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 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 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 Collocated 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 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 Collocated CoA mode, the Mobile Router MAY encapsulate one more times 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. But note that this might introduce significant overhead on the data packets as each level of nesting introduces another tunnel header encapsulation.

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. Here too, the purpose of NEMOv4 extensions is not to inform the Mobile Router about topology changes at home.

Examples of dynamic routing protocol include but are not limited to OSPF Version 2 RFC 2328 (Moy, J., “OSPF Version 2,” April 1998.) [RFC2328], BGP RFC 4271 (Rekhter, Y., Li, T., and S. Hares, “A Border Gateway Protocol 4 (BGP-4),” January 2006.) [RFC4271] and RIP RFC 2453 (Malkin, G., “RIP Version 2,” November 1998.) [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) efficiently avoid duplication of sent data or over-provisioning of 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 (Establishment of Bi-directional Tunnel)). If a network address and prefix about 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, in order to avoid incoherencies in the forwarding information bases. The Mobile Router SHOULD use NEMOv4 implicit mode in this case (see Section 3 (Requirements)).

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 (Security when Dynamic Routing Protocol is Used) apply.

10.  Security Considerations

The Mobile Network extension is protected by the same rules for Mobile IP extensions in registration messages. See the Security Considerations section in RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [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. A registration failure MUST be notified to the mobile router when it cannot be successfully authorized for prefixes requested by it.

All registration requests and replies MUST be authenticated by the MN-HA Authentication Extension as specified in RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] and its update (Perkins, C., “IP Mobility Support for IPv4, revised,” April 2010.) [I‑D.ietf‑mip4‑rfc3344bis]. 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.

A routing protocol message protected with ESP, and sent through the Mobile Router - Home Agent bidirectional tunnel, SHOULD NOT contain the Mobile IPv4 Mobile-Home Authentication Extension, since ESP provides enough security.

11.  IANA Considerations

IANA to modify 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.

The new Values and Names for the Type for Extensions appearing in Mobile IP control messages are the following:

A new number space should be 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:

The policy of future assignments to this number space should be following Expert Review.

The new Code Values for Mobile IP Registration Reply messages are the following (for a registration denied by the Home Agent):

A new number space should be 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):

The policy of future assignments to this number space should be following Expert Review.

The current non-modified numbering spaces could be consulted at the URL http://www.iana.org/assignments/mobileip-numbers (contents last updated 2007-12-20 and last browsed 2008-01-04).

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 draft. Hans Sjostrand (Hans Sj\"ostrand) identified the last clarifications with respect to Foreign Agent mode treatment. Pete McCann contributed necessary refinements of many statements.

13.  References

13.1. Normative References

13.2. Informative References

Appendix A.  ChangeLog

The changes are listed in reverse chronological order, most recent changes appearing at the top of the list.

From draft-ietf-mip4-nemo-v4-base-06.txt to draft-ietf-mip4-nemo-v4-base-07.txt

• encoded the draft into xml. Compiled with xml2rfc version 1.33pre4.
• checked against 'idnits' script version 2.05.03.
• substituted 'Care-of Address' for 'CoA'.

From draft-ietf-mip4-nemo-v4-base-05.txt to draft-ietf-mip4-nemo-v4-base-06.txt

• substituted "TBA" for "1" in Sub-type of Mobile Network Request Extension.
• substituted "TBA" for "0" in Code of Mobile Network Acknowledgement Extension and in the IANA Section.
• modified the IANA section to request definition two new spaces (instead of just defining new values) for Sub-Type of Mobile Network Extensions and for Code Values for Mobile Network Acknowledgement Extension, and to suggest "Expert Review" as method of new assignments in these two spaces (and not necessarily "IETF Consensus").

From draft-ietf-mip4-nemo-v4-base-04.txt to draft-ietf-mip4-nemo-v4-base-05.txt

• updated the Acknowledgements section.
• capitalized all occurences of "Home Address", "Mobile Router" and "Care-of Address".
• refined many statements.
• checked against 'idnits' script version 2.04.16.

From draft-ietf-mip4-nemo-v4-base-03.txt to draft-ietf-mip4-nemo-v4-base-04.txt

• more changes in Introduction to say that with FA mode only the non-optimized double-encapsulation operation is supported and [I‑D.ietf‑mip4‑nemov4‑fa] (Tsirtsis, G., Park, V., Narayanan, V., and K. Leung, “FA extensions to NEMOv4 Base,” April 2008.) proposes a optimization.

From draft-ietf-mip4-nemo-v4-base-02.txt to draft-ietf-mip4-nemo-v4-base-03.txt

• changed a sentence in the Introduction to say that FA mode _is_ supported but unoptimized, and that a reference (Tsirtsis, G., Park, V., Narayanan, V., and K. Leung, “FA extensions to NEMOv4 Base,” April 2008.) [I‑D.ietf‑mip4‑nemov4‑fa] optimizes that mode.
• added reference (Perkins, C., “IP Mobility Support for IPv4, revised,” April 2010.) [I‑D.ietf‑mip4‑rfc3344bis] to the rfc3344bis draft.

From draft-ietf-mip4-nemo-v4-base-01.txt to draft-ietf-mip4-nemo-v4-base-02.txt

• changed title from "IPv4 Network Mobility (NEMO) Protocol" to "Network Mobility (NEMO) Extensions for Mobile IPv4".

From draft-ietf-mip4-nemo-v4-base-00.txt to draft-ietf-mip4-nemo-v4-base-01.txt

• added a section on Routing Protocol between Mobile Router and Home Agent.
• added a security subsection about running simultaneously a secure routing protocol with secure Mobile IPv4.
• added a date tag on the IANA URL for Mobile IP numbering spaces.
• substituted 'Mobile Router' for 'MR' everywhere.
• updated reference to NEMOv4 FA draft.

From draft-ietf-nemo-v4-base-01.txt to draft-ietf-mip4-nemo-v4-base-00.txt:

• changed draft name, headers and footers.
• changed title.
• a more coherent use of terms 'subnet', 'prefix' and 'mobile network'.
• clarified only co-located CoA mode is supported (not FA CoA) for Mobile Routers in this specification. And added reference to the FA NEMO optimizations draft.
• changed 'devices' to 'hosts'.
• changed 'moving networks' to 'mobile networks'.
• clarified what 'reachability' in a certain context is: packets may be dropped if ingress filtering is turned on.
• removed the MR-FA-CoA tunnel overhead optimization. There is still an issue with text at HA doing optimization.

This document was first presented as an individual contribution to the NEMO Working Group, then adopted as a WG item to that group. The 01 version in the NEMO WG has been Last Called on the INFORMATIONAL track. The evolution was:

From version draft-ietf-nemo-v4-base-00 to draft-ietf-nemo-v4-base-01:

• removed error code HA_MOBNET_UNSUPPORTED.
• changed all values to be assigned by IANA, from specific numbers to "TBA" (To Be Assigned).
• substituted "egress interface" for "roaming interface".
• changed HA behaviour upon reception of MNPs. In 00 the HA replied positively only if all MNPs in RegReq were valid, in 01 a reply is constructed specifying which MNP was valid and which not.
• clarified a 3-line paragraph saying that RegRep may contain both implicit and explicit acknowledgements.

Authors' Addresses

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