NETLMM Working Group                                V. Devarapalli (ed.)
Internet-Draft                                                  WiChorus
Intended status: Standards Track                         R. Koodli (ed.)
Expires: September 24, October 11, 2009                               Starent Networks
                                                                  H. Lim
                                                                 N. Kant
                                                             S. Krishnan
                                                             J. Laganier
                                                        DOCOMO Euro-Labs
                                                          March 23,
                                                           April 9, 2009

               Heartbeat Mechanism for Proxy Mobile IPv6

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   Proxy Mobile IPv6 is a network-based mobility management protocol.
   The mobility entities involved in the Proxy Mobile IPv6 protocol, the
   Mobile Access Gateway (MAG) and the Local Mobility Anchor (LMA),
   setup tunnels dynamically to manage mobility for a mobile node within
   the Proxy Mobile IPv6 domain.  This document describes a heartbeat
   mechanism between the MAG and the LMA to detect failures failures, quickly
   inform peers in the event of a recovery from node failures, and allow
   a peer to take appropriate action.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3  4
   3.  Heartbeat Mechanism  . . . . . . . . . . . . . . . . . . . . .  3  4
     3.1.  Failure Detection  . . . . . . . . . . . . . . . . . . . .  4  5
     3.2.  Restart Detection  . . . . . . . . . . . . . . . . . . . .  5  6
     3.3.  Heartbeat Message  . . . . . . . . . . . . . . . . . . . .  6  7
     3.4.  Restart Counter Mobility Option  . . . . . . . . . . . . .  7  8
   4.  Exchanging Heartbeat Messages over an IPv4 Transport
       Network  . . . . . . . . . . . . . . . . . . . . . . . . . . .  8  9
   5.  Configuration Variables  . . . . . . . . . . . . . . . . . . .  8  9
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9 10
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9 10
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  9 10
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 11
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 10 11
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 10 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 11

1.  Introduction

   Proxy Mobile IPv6 [RFC5213] enables network-based mobility for IPv6
   hosts that do not implement any mobility protocols.  The protocol is
   described in detail in [RFC5213].  In order to facilitate the
   network-based mobility, the PMIPv6 protocol defines a Mobile Access
   Gateway (MAG), which acts as a proxy for the Mobile IPv6 [RFC3775]
   signaling, and the Local Mobility Anchor (LMA) which acts similar to
   a Home Agent, anchoring a Mobile Node's sessions within a Proxy
   Mobile IPv6 (PMIPv6) domain.  The LMA and the MAG establish a
   bidirectional tunnel for forwarding all data traffic belonging to the
   Mobile Nodes.

   In a distributed environment such as a PMIPv6 domain consisting of
   LMA and MAGs, it is necessary for the nodes to 1) have a consistent
   state about each other's reachability, and 2) quickly inform peers in
   the event of recovery from node failures.  So, when the LMA restarts
   after a failure, the MAG should (quickly) learn about the restart so
   that it could take appropriate actions (such as releasing any
   resources).  When there are no failures, a MAG should know about
   LMA's reachability (and vice versa) so that the path can be assumed
   to be functioning.

   This document specifies a heartbeat mechanism between the MAG and the
   LMA to detect the status of reachability between them.  This document
   also specifies a mechanism to indicate node restarts; the mechanism
   could be used to quickly inform peers of such restarts.  The
   heartbeat message is a mobility header message (protocol type 135)
   which is periodically exchanged at a configurable threshold of time
   or sent unsolicited soon after a node restart.  This document does
   not specify the specific actions (such as releasing resources) that a
   node takes as a response to processing the heartbeat messages.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Heartbeat Mechanism

   The MAG and the LMA exchange heartbeat messages every
   HEARTBEAT_INTERVAL seconds to detect the current status of
   reachability between them.  The MAG initiates the heartbeat exchange
   to test if the LMA is reachable by sending a Heartbeat Request
   message to the LMA.  Each Heartbeat Request contains a sequence
   number that is incremented monotonically.  The sequence number on the
   last Heartbeat Request message is always recorded by the MAG, and is
   used to match the corresponding Heartbeat Response.  Similarly, the
   LMA also initiates a heartbeat exchange with the MAG, by sending a
   Heartbeat Request message, to check if the MAG is reachable.  The
   format of the Heartbeat message is described in Section 3.3.

   A Heartbeat Request message can be sent only if the MAG has at least
   one proxy binding cache entry at the LMA for a mobile node attached
   to the MAG.  If there are no proxy binding cache entries at the LMA
   for any of the mobile nodes attached to the MAG, then the heartbeat
   message SHOULD NOT be sent.  Similarly, the LMA SHOULD NOT send a
   Heartbeat Request message to a MAG if there is no active binding
   cache entry created by the MAG.  A PMIPv6 node MUST respond to a
   Heartbeat Request message with a Heartbeat Response message,
   irrespective of whether there is an active binding cache entry.

   The HEARTBEAT_INTERVAL SHOULD NOT be configured to a value less than
   30 seconds.  Deployments should be careful in setting the value for
   the HEARTBEAT_INTERNVAL.  Sending heartbeat messages too often may
   become an overhead on the path between the MAG and the LMA.  It could
   also create congestion in the network and negatively affect network
   performance.  The HEARTBEAT_INTERVAL can be set to a much larger
   value on the MAG and the LMA, if required, to reduce the burden of
   sending periodic heartbeat messages.

   If the LMA or the MAG do not support the heartbeat messages, they
   respond with a Binding Error message with status set to '2'
   (unrecognized MH type value) as described in [RFC3775].  When the
   Binding Error message with status set to '2' is received in response
   to Heartbeat Request message, the initiating MAG or the LMA MUST NOT
   use heartbeat messages with the other end again.

   If a PMIPv6 node has detected that a peer PMIPv6 node has failed or
   restarted without retaining the PMIPv6 session state, it should mark
   the corresponding binding update list or binding cache entries as
   invalid.  The PMIPv6 node may also take other actions which are
   outside the scope of this document.

   The detection of failures and restarts events may be signaled to
   network operators by using asynchronous notifications.  Future work
   may define such notifications in a SMIv2 Management Information Base
   (MIB) module.

3.1.  Failure Detection

   A PMIPv6 node, (MAG or LMA) matches every received Heartbeat Response
   to the Heartbeat Request sent using the sequence number.  Before
   sending the next Heartbeat Request, it increments a local variable
   MISSING_HEARTBEAT if it has not received a Heartbeat Response for the
   previous request.  When this local variable MISSING_HEARTBEAT exceeds
   a configurable parameter MISSING_HEARTBEATS_ALLOWED, the PMIPv6 node
   concludes that the peer PMIPv6 node is not reachable.  If a Heartbeat
   Response message is received, the MISSING_HEARTBEATS counter is

3.2.  Restart Detection

   The section describes a mechanism for detecting failure recovery
   without session persistence.  In case the LMA or the MAG crashes and
   re-boots and loses all state with respect to the PMIPv6 sessions, it
   would be beneficial for the peer PMIPv6 node to discover the failure
   and the loss of session state and establish the sessions again.

   Each PMIPv6 node (both the MAG and LMA) MUST maintain a monotonically
   increasing Restart Counter that is incremented every time the node
   re-boots and looses PMIPv6 session state.  The counter MUST NOT be
   incremented if the recovery happens without losing state for the
   PMIPv6 sessions active at the time of failure.  This counter MUST be
   treated as state that is preserved across reboots.  A PMIPv6 node
   includes a Restart Counter mobility option, described in Section 3.4
   in an Heartbeat Response message to indicate the current value of the
   Restart Counter.  Each PMIPv6 node MUST also store the Restart
   Counter for all the peer PMIPv6 nodes that it has sessions with
   currently.  Storing the Restart Counter values for peer PMIPv6 nodes
   does not need to be preserved across reboots.

   The PMIPv6 node that receives the Heartbeat Response message compares
   the Restart Counter value with the previously received value.  If the
   value is different, the receiving node assumes that the peer PMIPv6
   node had crashed and recovered.  If the Restart Counter value changes
   or if there was no previously stored value, the new value is stored
   by the receiving PMIPv6 node.

   If a PMIPv6 node restarts and looses PMIPv6 session state, it SHOULD
   send an unsolicited Heartbeat Response message with an incremented
   Restart Counter to all the PMIPv6 nodes that had previously
   established PMIPv6 sessions.  Note that this is possible only when
   the PMIPv6 node is capable of storing information about the peers
   across reboots.  The unsolicited Heartbeat Response message allows
   the peer PMIPv6 nodes to quickly discover the restart.  The sequence
   number field in the unsolicited Heartbeat Response is ignored and no
   response is necessary; the nodes will synchronize during the next
   Request and Response exchange.

3.3.  Heartbeat Message

   The Heartbeat Message is based on the Mobility Header defined in
   Section 6.1 of [RFC3775].  The 'MH type' field in the Mobility Header
   indicates that it is a Heartbeat Message.  The value MUST be set to
   <IANA-TBD1>.  This document does not make any other changes to the
   Mobility Header message.  Please refer to [RFC3775] for a description
   of the fields in the Mobility Header Message.

      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
     | Payload Proto |  Header Len   |   MH Type     |   Reserved    |
     |           Checksum            |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
     |                                                               |
     .                                                               .
     .                       Message Data                            .
     .                                                               .
     |                                                               |

                 Figure 1: Mobility Header Message Format

   The Heartbeat Message follows the 'Checksum' field in the above
   message.  The following illustrates the message format for the
   Heartbeat Mobility Header message.

      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
                                     |            Reserved       |U|R|
     |                       Sequence Number                         |
     |                                                               |
     .                                                               .
     .                        Mobility options                       .
     .                                                               .
     |                                                               |

                    Figure 2: Heartbeat Message Format

      Set to 0 and ignored by the receiver.


      Set to 1 in Unsolicited Heartbeat Response.  Otherwise set to 0.


      A 1-bit flag that indicates whether the message is a request or a
      response.  When the 'R' flag is set to 0, it indicates that the
      Heartbeat message is a request.  When the 'R' flag is set to 1, it
      indicates that the Heartbeat message is a response.

   Sequence Number

      A 32-bit sequence number used for matching the request to the

   Mobility Options

      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 receiver
      MUST ignore and skip any options which it does not understand.  At
      the time of writing this document, the Restart Counter Mobility
      Option, described in Section 3.4, is the only valid option in this

3.4.  Restart Counter Mobility Option

   The following shows the message format for a new mobility option for
   carrying the Restart Counter Value in the Heartbeat message.  The
   Restart Counter Mobility Option is only valid in a Heartbeat Response
   message.  It has an alignment requirement of 4n+2.

      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    |
     |                       Restart Counter                         |

                 Figure 3: Restart Counter Mobility Option

      A 8-bit field that indicates that it is a Restart Counter mobility
      option.  It MUST be set to <IANA-TBD2>.


      A 8-bit field that indicates the length of the option in octets
      excluding the 'Type' and 'Length' fields.  It is set to '4'.

   Restart Counter

      A 32-bit field that indicates the current Restart Counter value.

4.  Exchanging Heartbeat Messages over an IPv4 Transport Network

   In some deployments, the network between the MAG and the LMA may not
   be capable of transporting IPv6 packets.  In this case, the Heartbeat
   messages are tunneled over IPv4.  If the Proxy Binding Update and
   Proxy Binding Acknowledgment messages are sent using UDP
   encapsulation to traverse NATs, then the Heartbeat messages are also
   sent with UDP encapsulation.  The UDP port used would be the same as
   the port used for the Proxy Binding Update and Proxy Binding
   Acknowledgement messages.  For more details on tunneling Proxy Mobile
   IPv6 signaling messages over IPv4, see

5.  Configuration Variables

   The LMA and the MAG must allow the following variables to be


      This variable is used to set the time interval in seconds between
      two consecutive Heartbeat Request messages.  The default value is
      60 seconds.  It SHOULD NOT be set to less than 30 seconds or
      larger than 3600 seconds.


      This variable indicates the maximum number of consecutive
      Heartbeat Request messages that a PMIPv6 node did not receive a
      response for before concluding that the peer PMIPv6 node is not
      reachable.  The default value for this variable is 3.

6.  Security Considerations

   The heartbeat messages are just used for checking reachability
   between the MAG and the LMA.  They do not carry information that is
   useful for eavesdroppers on the path.  Therefore, confidentiality
   protection is not required.  Integrity protection using IPsec
   [RFC4301] for the heartbeat messages MUST be supported on the MAG and
   the LMA.  RFC 5213 [RFC5213] describes how to protect the Proxy
   Binding Update and Acknowledgment signaling messages with IPsec.  The
   Heartbeat message defined in this specification is merely another
   subtype of the same Mobility Header protocol that is already being
   protected by IPsec.  Therefore, protecting this additional message is
   possible using the mechanisms and security policy models from these
   RFCs.  The security policy database entries should use the new MH
   Type, the Heartbeat Message, for the MH Type selector.

   If dynamic key negotiation between the MAG and the LMA is required,
   IKEv2 [RFC4306] should be used.

7.  IANA Considerations

   The Heartbeat message defined in Section 3.3 must have the type value
   allocated from the same space as the 'MH Type' name space in the
   Mobility Header defined in RFC 3775 [RFC3775].

   The Restart Counter mobility option defined in Section 3.4 must have
   the type value allocated from the same name space as the Mobility
   Options defined in RFC 3775 [RFC3775].

8.  Acknowledgments

   A heartbeat mechanism for a network-based mobility management
   protocol was first described in [I-D.giaretta-netlmm-dt-protocol].
   The authors would like to thank the members of a NETLMM design team
   that produced that document.  The mechanism described in this
   document also derives from the path management mechanism described in

   We would like to thank Alessio Casati for first suggesting a fault
   handling mechanism for Proxy Mobile IPv6.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

              Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
              Mobile IPv6", draft-ietf-netlmm-pmip6-ipv4-support-08 draft-ietf-netlmm-pmip6-ipv4-support-10
              (work in progress), January March 2009.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

9.2.  Informative References

              Giaretta, G., "The NetLMM Protocol",
              draft-giaretta-netlmm-dt-protocol-02 (work in progress),
              October 2006.

   [GTP]      3rd Generation Partnership Project, "3GPP Technical
              Specification 29.060 V7.6.0: "Technical Specification
              Group Core Network and Terminals; General Packet Radio
              Service (GPRS); GPRS Tunnelling Protocol (GTP) across the
              Gn and Gp interface (Release 7)"", July 2007.

Authors' Addresses

   Vijay Devarapalli
   3950 North First Street
   San Jose, CA  95134

   Rajeev Koodli
   Starent Networks


   Heeseon Lim
   5403 Betsy Ross Drve
   Santa Clara, CA  95054


   Nishi Kant
   5403 Betsy Ross Drive
   Santa Clara, CA  95054


   Suresh Krishnan
   8400 Decarie Blvd.
   Town of Mount Royal, QC


   Julien Laganier
   DOCOMO Euro-Labs
   Landsbergerstrasse 312
   Munich, D-80687