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rfc:rfc5142

Network Working Group B. Haley Request for Comments: 5142 Hewlett-Packard Category: Standards Track V. Devarapalli

                                                       Azaire Networks
                                                               H. Deng
                                                          China Mobile
                                                              J. Kempf
                                                       DoCoMo USA Labs
                                                          January 2008
             Mobility Header Home Agent Switch Message

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 specifies a new Mobility Header message type that can
 be used between a home agent and mobile node to signal to a mobile
 node that it should acquire a new home agent.

Haley, et al. Standards Track [Page 1] RFC 5142 Home Agent Switch Message January 2008

Table of Contents

 1. Introduction ....................................................2
 2. Terminology .....................................................3
 3. Scenarios .......................................................3
    3.1. Overloaded .................................................3
    3.2. Load Balancing .............................................3
    3.3. Maintenance ................................................3
    3.4. Functional Load Balancing ..................................3
    3.5. Home Agent Renumbering .....................................4
 4. Home Agent Switch Message .......................................4
 5. Home Agent Operation ............................................6
    5.1. Sending Home Agent Switch Messages .........................6
    5.2. Retransmissions ............................................7
    5.3. Mobile Node Errors .........................................7
 6. Mobile Node Operation ...........................................8
    6.1. Receiving Home Agent Switch Messages .......................8
    6.2. Selecting a Home Agent .....................................9
 7. Operational Considerations ......................................9
 8. Protocol Constants .............................................10
 9. IANA Considerations ............................................10
 10. Security Considerations .......................................10
 11. References ....................................................11
    11.1. Normative References .....................................11
    11.2. Informative References ...................................11
 Acknowledgments ...................................................11

1. Introduction

 RFC 3775 [RFC3775] contains no provision to allow a home agent to
 inform a mobile node that it needs to stop acting as the home agent
 for the mobile node.  For example, a home agent may wish to handoff
 some of its mobile nodes to another home agent because it has become
 overloaded or it is going offline.
 This protocol describes a signaling message, called the Home Agent
 Switch message, that can be used to send a handoff notification
 between a home agent and mobile node.
 The Home Agent Switch message does not attempt to solve all general
 problems related to changing the home agent of a mobile node.  In
 particular, this protocol does not attempt to solve:
    o  The case where the Home Address of a mobile node must change in
       order to switch to a new home agent.  This operation should be
       avoided using this message.

Haley, et al. Standards Track [Page 2] RFC 5142 Home Agent Switch Message January 2008

    o  Determining when a home agent should actively move mobile nodes
       to another home agent.  This decision should be made by a
       backend protocol, for example, as described in [hareliability].

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].

3. Scenarios

 Here are some example scenarios where a home agent signaling message
 would be useful.

3.1. Overloaded

 There are a number of reasons a home agent might be considered
 overloaded.  One might be that it is at, or near, its limit on the
 number of home bindings it is willing to accept.  Another is that it
 has reached a pre-determined level of system resource usage --
 memory, cpu cycles, etc.  In either case, it would be desirable for a
 home agent to reduce the number of home bindings before a failure
 occurs.

3.2. Load Balancing

 A home agent might know of other home agents that are not as heavily
 loaded as itself, learned through some other mechanism outside the
 scope of this document.  An operator may wish to try and balance this
 load so that a failure would disrupt a smaller percentage of mobile
 nodes.

3.3. Maintenance

 Most operators do periodic maintenance in order to maintain
 reliability.  If a home agent is being shutdown for maintenance, it
 would be desirable to inform mobile nodes so they do not lose
 mobility service.

3.4. Functional Load Balancing

 A Mobile IPv6 home agent provides mobile nodes with two basic
 services.  It acts as a rendezvous server where correspondent nodes
 can find the current care-of address for the mobile node, and as an
 overlay router to tunnel traffic to/from the mobile node at its
 current care-of address.

Haley, et al. Standards Track [Page 3] RFC 5142 Home Agent Switch Message January 2008

 A mobility service provider could have two sets of home agents to
 handle the two functions.  The rendezvous function could be handled
 by a machine specialized for high-speed transaction processing, while
 the overlay router function could be handled by a machine with high
 data throughput.
 A mobile node would start on the rendezvous server home agent and
 stay there if it does route optimization.  However, if the original
 home agent detects that the mobile node is not doing route
 optimization, but instead reverse-tunneling traffic, it could
 redirect the mobile node to a home agent with better data throughput.

3.5. Home Agent Renumbering

 Periodically, a mobility service provider may want to shut-down home
 agent services at a set of IPv6 addresses and bring service back up
 at a new set of addresses.  Note that this may not involve anything
 as complex as IPv6 network renumbering [RFC4192]; it may just involve
 changing the addresses of the home agents.  With a signaling message,
 the service provider could inform mobile nodes to look for a new home
 agent.

4. Home Agent Switch Message

 The Home Agent Switch message is used by the home agent to signal to
 the mobile node that it needs to stop acting as the home agent for
 the mobile node, and that it should acquire a new home agent.  Home
 Agent Switch messages are sent as described in Section 5.
 The message described below follows the Mobility Header format
 specified in Section 6.1 of [RFC3775]:
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Payload Proto |  Header Len   |   MH Type     |   Reserved    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Checksum            |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
    |                                                               |
    .                                                               .
    .                       Message Data                            .
    .                                                               .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Haley, et al. Standards Track [Page 4] RFC 5142 Home Agent Switch Message January 2008

 The Home Agent Switch Message uses the MH Type value (12).  When this
 value is indicated in the MH Type field, the format of the Message
 Data field in the Mobility Header 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
                                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                    |# of Addresses |   Reserved    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    .                                                               .
    .                      Home Agent Addresses                     .
    .                                                               .
    +                                                               +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    .                                                               .
    .                        Mobility Options                       .
    .                                                               .
    +                                                               +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 # of Addresses
    An 8-bit unsigned integer indicating the number of IPv6 home agent
    addresses in the message.  If set to zero, the mobile node MUST
    perform home agent discovery.
 Reserved
    An 8-bit field reserved for future use.  The value MUST be
    initialized to zero by the sender, and MUST be ignored by the
    receiver.
 Home Agent Addresses
    A list of alternate home agent addresses for the mobile node.  The
    number of addresses present in the list is indicated by the "# of
    Addresses" field in the Home Agent Switch message.

Haley, et al. Standards Track [Page 5] RFC 5142 Home Agent Switch Message January 2008

 Mobility Options
    A Variable-length field of such length that the complete Mobility
    Header is an integer multiple of 8 octets long.  This field
    contains zero or more TLV-encoded mobility options.  The encoding
    and format of defined options MUST follow the format specified in
    Section 6.2 of [RFC3775].  The receiver MUST ignore and skip any
    options that it does not understand.
    The Binding Refresh Advice mobility option defined in Section
    6.2.4 of [RFC3775] is valid for the Home Agent Switch message.
 If no home agent addresses and no options are present in this
 message, no padding is necessary and the Header Len field in the
 Mobility Header will be set to zero.

5. Home Agent Operation

5.1. Sending Home Agent Switch Messages

 When sending a Home Agent Switch message, the sending node constructs
 the packet as it would any other Mobility Header, except:
    o  The MH Type field MUST be set to (12).
    o  If alternative home agent addresses are known, the sending home
       agent SHOULD include them in the list of suggested alternate
       home agents.  The home agent addresses field should be
       constructed as described in Section 10.5.1 of [RFC3775], which
       will randomize addresses of the same preference in the list.
    o  The "# of Addresses" field MUST be filled-in corresponding to
       the number of home agent addresses included in the message.  If
       no addresses are present, the field MUST be set to zero,
       forcing the mobile node to perform home agent discovery by some
       other means.
    o  If the home agent is able to continue offering services to the
       mobile node for some period of time, it MAY include a Binding
       Refresh Advice mobility option indicating the time (in units of
       4 seconds) until the binding will be deleted.
 The Home Agent Switch message MUST use the home agent to mobile node
 IPsec ESP (Encapsulating Security Payload) authentication SA
 (Security Association) for integrity protection.

Haley, et al. Standards Track [Page 6] RFC 5142 Home Agent Switch Message January 2008

 A home agent SHOULD send a Home Agent Switch message when a known
 period of unavailability is pending so the mobile node has sufficient
 time to find another suitable home agent.
 The sending node does not need to be the current home agent for the
 mobile node, for example as described in [hareliability], but it MUST
 have a security association with the mobile node so the message is
 not rejected.  In this case, the Home Agent Switch message SHOULD
 only contain the address of the home agent sending the message in the
 Home Agent Addresses field, which implies that the mobile node should
 switch to using the sender as its new home agent.

5.2. Retransmissions

 If the home agent does not receive a response from the mobile node --
 either a Binding Update message to delete its home binding if it is
 the current home agent, or a Binding Update message to create a home
 binding if it is not the current home agent -- then it SHOULD
 retransmit the message until a response is received.  The initial
 value for the retransmission timer is INITIAL-HA-SWITCH-TIMEOUT.
 The retransmissions by the home agent MUST use an exponential back-
 off mechanism, in which the timeout period is doubled upon each
 retransmission, until either the home agent gets a response from the
 mobile node to delete its binding, or the timeout period reaches the
 value MAX-HA-SWITCH-TIMEOUT.  The home agent MAY continue to send
 these messages at this slower rate indefinitely.
 If the home agent included a Binding Refresh Advice mobility option,
 then it SHOULD delay any retransmissions until at least one half of
 the time period has expired, or INITIAL-HA-SWITCH-TIMEOUT, whichever
 value is less.

5.3. Mobile Node Errors

 If a mobile node does not understand how to process a Home Agent
 Switch message, it will send a Binding Error message as described in
 Section 6.1.
 If a mobile node is unreachable, in other words, it still has a home
 binding with the home agent after reaching the timeout period of MAX-
 HA-SWITCH-TIMEOUT, the home agent SHOULD NOT make any conclusions
 about its status.
 In either case, the home agent SHOULD attempt to continue providing
 services until the lifetime of the binding expires.

Haley, et al. Standards Track [Page 7] RFC 5142 Home Agent Switch Message January 2008

 Attempts by the mobile node to extend the binding lifetime with a
 Binding Update message SHOULD be rejected, and a Binding
 Acknowledgement SHOULD be returned with status value 129
 (Administratively prohibited) as specified in Section 6.1.8 of
 [RFC3775].

6. Mobile Node Operation

6.1. Receiving Home Agent Switch Messages

 Upon receiving a Home Agent Switch message, the Mobility Header MUST
 be verified as specified in [RFC3775], specifically:
    o  The Checksum, MH type, Payload Proto, and Header Len fields
       MUST meet the requirements of Section 9.2 of [RFC3775].
    o  The packet MUST be covered by the home agent to mobile node
       IPsec ESP authentication SA for integrity protection.
 If the packet is dropped due to the above tests, the receiving node
 MUST follow the processing rules as Section 9.2 of [RFC3775] defines.
 For example, it MUST send a Binding Error message with the Status
 field set to 2 (unrecognized MH Type value) if it does not support
 the message type.
 Upon receipt of a Home Agent Switch message, the mobile node MUST
 stop using its current home agent for services and MUST delete its
 home binding by sending a Binding Update message as described in
 Section 11.7.1 of [RFC3775].  This acts as an acknowledgement of the
 Home Agent Switch message.  Alternately, if the sender of the message
 is not the current home agent, sending a Binding Update message to
 create a home binding will act as an acknowledgement of the Home
 Agent Switch message.  Retransmissions of Binding Update messages
 MUST use the procedures described in Section 11.8 of [RFC3775].
 If a Binding Refresh Advice mobility option is present, the mobile
 node MAY delay the deletion of its home binding and continue to use
 its current home agent until the calculated time period has expired.
 If the Home Agent Switch message contains a list of alternate home
 agent addresses, the mobile node SHOULD select a new home agent as
 described in Section 6.2, and establish the necessary IPsec security
 associations with the new home agent by whatever means required as
 part of the mobile node/home agent bootstrapping protocol for the
 home agent's mobility service provider.  If no alternate home agent
 addresses are included in the list, the mobile node MUST first
 perform home agent discovery.

Haley, et al. Standards Track [Page 8] RFC 5142 Home Agent Switch Message January 2008

6.2. Selecting a Home Agent

 In most cases, the home agent addresses in the Home Agent Switch
 message will be of other home agents on the home link of the mobile
 node (the computed prefix is the same).  In this case, the mobile
 node SHOULD select a new home agent from the addresses as they are
 ordered in the list.  If the first address in the list is unable to
 provide service, then the subsequent addresses in the list should be
 tried in-order.
 In the case that the home agent addresses in the Home Agent Switch
 message are not all home agents on the home link of the mobile node
 (the computed prefix is different), the mobile node SHOULD select one
 with its home network prefix first, if available, followed by home
 agents with other prefixes.  Choosing a home agent with a different
 prefix might require a change of the home address for the mobile
 node, which could cause a loss of connectivity for any connections
 using the current home address.

7. Operational Considerations

 This document does not specify how an operator might use the Home
 Agent Switch message in its network.  However, the following
 requirements are placed on its usage:
    o  The use of this message needs to take into account possible
       signaling overhead, congestion, load from the mechanism itself,
       and the resulting registration to another home agent.  A home
       agent may provide service for thousands, if not millions, of
       mobile nodes.  Careless application of the Home Agent Switch
       message may cause the new home agent, or some other parts of
       the network, to suffer.  As a result, it is REQUIRED that
       applications of this message either employ a feedback loop
       between resources of the new home agent and the sending of
       additional Home Agent Switch messages, or apply a maximum rate
       at which mobile nodes can be informed of the switch that is far
       below the designated capacity of new registrations that the set
       of home agents can process.  If no other information is
       available, this maximum rate should default to MAX-HA-SWITCH-
       TRANSMIT-RATE.
    o  In general, switching the home agent of a mobile node should
       only be done when absolutely necessary, since it might cause a
       service disruption if the switch to a new home agent fails, the
       new home agent is itself under an overload condition, or the
       network connection of the new home agent is congested.

Haley, et al. Standards Track [Page 9] RFC 5142 Home Agent Switch Message January 2008

       Similarly, the path characteristics via the new home agent may
       be different, which may cause temporary difficulties for end-
       to-end transport layer operation.
    o  If this message is being used for load-balancing between a set
       of home agents, they should all be configured with the same set
       of prefixes so a home agent switch does not require a change of
       the home address for a mobile node.  That operation is NOT
       RECOMMENDED and should be avoided.

8. Protocol Constants

 INITIAL-HA-SWITCH-TIMEOUT             5 seconds
 MAX-HA-SWITCH-TIMEOUT                 20 seconds
 MAX-HA-SWITCH-TRANSMIT-RATE           1 per second

9. IANA Considerations

 IANA has assigned a new Mobility Header type for the following new
 message described in Section 4:
    (12) Home Agent Switch message

10. Security Considerations

 As with other messages in [RFC3775], the Home Agent Switch message
 MUST use the home agent to mobile node ESP encryption SA for
 confidentiality protection, and MUST use the home agent to mobile
 node ESP authentication SA for integrity protection.
 The Home Agent Switch message MAY use the IPsec ESP SA in place for
 Binding Updates and Acknowledgements, as specified in Section 5.1 of
 [RFC3775], in order to reduce the number of configured security
 associations.  This also gives the message authenticity protection.
 Some operators may not want to reveal the list of home agents to on-
 path listeners.  In such a case, the Home Agent Switch message should
 use the home agent to mobile node IPsec ESP encryption SA for
 confidentiality protection.

Haley, et al. Standards Track [Page 10] RFC 5142 Home Agent Switch Message January 2008

11. References

11.1. Normative References

 [RFC2119]       Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3775]       Johnson, D., Perkins, C., and J. Arkko, "Mobility
                 Support in IPv6", RFC 3775, June 2004.

11.2. Informative References

 [RFC4192]       Baker, F., Lear, E., and R. Droms, "Procedures for
                 Renumbering an IPv6 Network without a Flag Day", RFC
                 4192, September 2005.
 [hareliability] Wakikawa, R., Ed., "Home Agent Reliability Protocol",
                 Work in Progress, November 2007.

Acknowledgments

 We would like to thank the authors of a number of previous documents
 that contributed content to this RFC:
    o Ryuji Wakikawa, Pascal Thubert, and Vijay Devarapalli,
      "Inter Home Agents Protocol Specification", March 2006.
    o Hui Deng, Brian Haley, Xiaodong Duan, Rong Zhang, and Kai Zhang,
      "Load Balance for Distributed Home Agents in Mobile IPv6",
      October 2004.
    o James Kempf, "Extension to RFC 3775 for Alerting the Mobile Node
      to Home Agent Unavailability", October 2005.
    o Brian Haley and Sri Gundavelli, "Mobility Header Signaling
      Message", September 2007.
 Thanks also to Kilian Weniger, Jixing Liu, Alexandru Petrescu, Jouni
 Korhonen, and Wolfgang Fritsche for their review and feedback.

Haley, et al. Standards Track [Page 11] RFC 5142 Home Agent Switch Message January 2008

Author's Addresses

 Brian Haley
 Hewlett-Packard Company
 110 Spitbrook Road
 Nashua, NH 03062, USA
 EMail: brian.haley@hp.com
 Vijay Devarapalli
 Azaire Networks
 3121 Jay Street
 Santa Clara, CA 95054 USA
 EMail: vijay.devarapalli@azairenet.com
 James Kempf
 DoCoMo USA Labs
 181 Metro Drive
 Suite 300
 San Jose, CA 95110 USA
 EMail: kempf@docomolabs-usa.com
 Hui Deng
 China Mobile
 53A, Xibianmennei Ave.
 Xuanwu District
 Beijing 100053
 China
 EMail: denghui@chinamobile.com

Haley, et al. Standards Track [Page 12] RFC 5142 Home Agent Switch Message January 2008

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Haley, et al. Standards Track [Page 13]

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