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RFC 5568

 
 
 

Mobile IPv6 Fast Handovers

Part 2 of 3, p. 20 to 40
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6.  Message Formats

   All the ICMPv6 messages have a common Type specified in [RFC4443].
   The messages are distinguished based on the Subtype field (see
   below).  For all the ICMPv6 messages, the checksum is defined in
   [RFC4443].

6.1.  New Neighborhood Discovery Messages

6.1.1.  Router Solicitation for Proxy Advertisement (RtSolPr)

   Mobile nodes send Router Solicitation for Proxy Advertisement
   messages in order to prompt routers for Proxy Router Advertisements.
   All the Link-Layer Address options have the format defined in
   Section 6.4.3.

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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Type     |      Code     |             Checksum          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Subtype    |    Reserved   |            Identifier         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-

      Figure 4: Router Solicitation for Proxy Advertisement (RtSolPr)
                                  Message

      IP Fields:

         Source Address: An IP address assigned to the sending
         interface.

         Destination Address: The address of the access router or the
         all routers multicast address.

         Hop Limit: 255.  See RFC 2461.

      ICMP Fields:

         Type: 154

         Code: 0

         Checksum: The ICMPv6 checksum.

         Subtype: 2

         Reserved: MUST be set to zero by the sender and ignored by the
         receiver.

         Identifier: MUST be set by the sender so that replies can be
         matched to this Solicitation.

      Valid Options:

         Source Link-Layer Address: When known, the link-layer address
         of the sender SHOULD be included using the Link-Layer Address
         (LLA) option.  See the LLA option format below.

         New Access Point Link-Layer Address: The link-layer address or
         identification of the access point for which the MN requests
         routing advertisement information.  It MUST be included in all

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         RtSolPr messages.  More than one such address or identifier can
         be present.  This field can also be a wildcard address.  See
         the LLA option below.

   Future versions of this protocol may define new option types.
   Receivers MUST silently ignore any options that they do not recognize
   and continue processing the rest of the message.

   Including the source LLA option allows the receiver to record the
   sender's L2 address so that neighbor discovery can be avoided when
   the receiver needs to send packets back to the sender (of the RtSolPr
   message).

   When a wildcard is used for the New Access Point LLA, no other New
   Access Point LLA options must be present.

   A Proxy Router Advertisement (PrRtAdv) message should be received by
   the MN in response to an RtSolPr.  If such a message is not received
   in a timely manner (no less than twice the typical round trip time
   (RTT) over the access link, or 100 milliseconds if RTT is not known),
   it SHOULD resend the RtSolPr message.  Subsequent retransmissions can
   be up to RTSOLPR_RETRIES, but MUST use an exponential backoff in
   which the timeout period (i.e., 2xRTT or 100 milliseconds) is doubled
   prior to each instance of retransmission.  If Proxy Router
   Advertisement is not received by the time the MN disconnects from the
   PAR, the MN SHOULD send an FBU immediately after configuring a new
   CoA.

   When RtSolPr messages are sent more than once, they MUST be rate-
   limited with MAX_RTSOLPR_RATE per second.  During each use of an
   RtSolPr, exponential backoff is used for retransmissions.

6.1.2.  Proxy Router Advertisement (PrRtAdv)

   Access routers send Proxy Router Advertisement messages gratuitously
   if the handover is network-initiated or as a response to an RtSolPr
   message from an MN, providing the link-layer address, IP address, and
   subnet prefixes of neighboring routers.  All the Link-Layer Address
   options have the format defined in 6.4.3.

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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Type     |      Code     |           Checksum            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Subtype    |    Reserved   |           Identifier          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-

          Figure 5: Proxy Router Advertisement (PrRtAdv) Message

      IP Fields:

         Source Address: MUST be the link-local address assigned to the
         interface from which this message is sent.

         Destination Address: The Source Address of an invoking Router
         Solicitation for Proxy Advertisement or the address of the node
         the access router is instructing to handover.

         Hop Limit: 255.  See RFC 2461.

      ICMP Fields:

         Type: 154

         Code: 0, 1, 2, 3, 4, or 5.  See below.

         Checksum: The ICMPv6 checksum.

         Subtype: 3

         Reserved: MUST be set to zero by the sender and ignored by the
         receiver.

         Identifier: Copied from the Router Solicitation for Proxy
         Advertisement or set to zero if unsolicited.

      Valid Options in the following order:

         Source Link-Layer Address: When known, the link-layer address
         of the sender SHOULD be included using the Link-Layer Address
         option.  See the LLA option format below.

         New Access Point Link-Layer Address: The link-layer address or
         identification of the access point is copied from RtSolPr
         message.  This option MUST be present.

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         New Router's Link-Layer Address: The link-layer address of the
         access router for which this message is proxied.  This option
         MUST be included when the Code is 0 or 1.

         New Router's IP Address: The IP address of the NAR.  This
         option MUST be included when the Code is 0 or 1.

         New Router Prefix Information Option: Specifies the prefix of
         the access router the message is proxied for and is used for
         address auto-configuration.  This option MUST be included when
         Code is 0 or 1.  However, when this prefix is the same as what
         is used in the New Router's IP Address option (above), the
         Prefix Information option need not be present.

         New CoA Option: MAY be present when PrRtAdv is sent
         unsolicited.  The PAR MAY compute a new CoA using the NAR's
         prefix information and the MN's L2 address or by any other
         means.

   Future versions of this protocol may define new option types.
   Receivers MUST silently ignore any options they do not recognize and
   continue processing the message.

   Currently, Code values 0, 1, 2, 3, 4, and 5 are defined.

   A Proxy Router Advertisement with Code 0 means that the MN should use
   the [AP-ID, AR-Info] tuple (present in the options above) for
   movement detection and NCoA formulation.  In this case, the Option-
   Code field in the New Access Point LLA option is 1 to reflect the LLA
   of the access point for which the rest of the options are related.
   Multiple tuples may be present.

   A Proxy Router Advertisement with Code 1 means that the message has
   been sent unsolicited.  If a New CoA option is present following the
   New Router Prefix Information option, the MN MUST use the supplied
   NCoA and send an FBU immediately or else stand to lose service.  This
   message acts as a network-initiated handover trigger; see
   Section 3.3.  In this case, the Option-Code field in the New Access
   Point LLA option (see below) is 1 to reflect the LLA of the access
   point for which the rest of the options are related.

   A Proxy Router Advertisement with Code 2 means that no new router
   information is present.  Each New Access Point LLA option contains an
   Option-Code value (described below) that indicates a specific
   outcome.

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      When the Option-Code field in the New Access Point LLA option is
      5, handover to that access point does not require a change of CoA.
      This would be the case, for instance, when a number of access
      points are connected to the same router interface, or when
      network-based mobility management mechanisms ensure that the
      specific mobile node always observes the same prefix regardless of
      whether there is a separate router attached to the target access
      point.

      No other options are required in this case.

      When the Option-Code field in the New Access Point LLA option is
      6, the PAR is not aware of the Prefix Information requested.  The
      MN SHOULD attempt to send an FBU as soon as it regains
      connectivity with the NAR.  No other options are required in this
      case.

      When the Option-Code field in the New Access Point LLA option is
      7, it means that the NAR does not support fast handover.  The MN
      MUST stop fast handover protocol operations.  No other options are
      required in this case.

   A Proxy Router Advertisement with Code 3 means that new router
   information is only present for a subset of access points requested.
   The Option-Code field values (those defined above, as well as the
   value of 1) distinguish different outcomes for individual access
   points.

   A Proxy Router Advertisement with Code 4 means that the subnet
   information regarding neighboring access points is sent unsolicited,
   but the message is not a handover trigger, unlike when the message is
   sent with Code 1.  Multiple tuples may be present.

   A Proxy Router Advertisement with Code 5 means that the MN may use
   the new router information present for detecting movement to a new
   subnet, but the MN must perform DHCP [RFC3315] upon attaching to the
   NAR's link.  The PAR and NAR will forward packets to the PCoA of the
   MN.  The MN must still formulate an NCoA for transmitting FBU (using
   the information sent in this message), but that NCoA will not be used
   for forwarding packets.

   When a wildcard AP identifier is supplied in the RtSolPr message, the
   PrRtAdv message should include any 'n' [Access Point Identifier,
   Link-Layer Address option, Prefix Information Option] tuples
   corresponding to the PAR's neighborhood.

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6.2.  New Mobility Header Messages

   Mobile IPv6 uses a new IPv6 header type called Mobility Header
   [RFC3775].  The Handover Initiate, Handover Acknowledge, Fast Binding
   Update, Fast Binding Acknowledgment, and the (deprecated) Fast
   Neighbor Advertisement messages use the Mobility Header.

6.2.1.  Inter - Access Router Messages

6.2.1.1.  Handover Initiate (HI)

   The Handover Initiate (HI) is a Mobility Header message sent by an
   Access Router (typically a PAR) to another access router (typically a
   NAR) to initiate the process of an MN's handover.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                     |           Sequence #          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |S|U|  Reserved |      Code     |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               .
     |                                                               |
     .                                                               .
     .                          Mobility options                     .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 6: Handover Initiate (HI) Message

      IP Fields:

         Source Address: The IP address of the PAR

         Destination Address: The IP address of the NAR

         Sequence #: MUST be set by the sender so replies can be matched
         to this message.

         'S' flag: Assigned address configuration flag.  When set, this
         message requests a new CoA to be returned by the destination.
         MAY be set when Code = 0.  MUST be 0 when Code = 1.

         'U' flag: Buffer flag.  When set, the destination SHOULD buffer
         any packets toward the node indicated in the options of this
         message.  Used when Code = 0, SHOULD be set to 0 when Code = 1.

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         Code: 0 or 1.  See below

         Reserved: MUST be set to zero by the sender and ignored by the
         receiver.

      Valid Options:

         Link-Layer Address of MN: The link-layer address of the MN that
         is undergoing handover to the destination (i.e., NAR).  This
         option MUST be included so that the destination can recognize
         the MN.

         Previous Care-of Address: The IP address used by the MN while
         attached to the originating router.  This option SHOULD be
         included so that a host route can be established if necessary.

         New Care-of Address: The IP address the MN wishes to use when
         connected to the destination.  When the 'S' bit is set, the NAR
         MAY assign this address.

   The PAR uses a Code value of 0 when it processes an FBU with the PCoA
   as source IP address.  The PAR uses a Code value of 1 when it
   processes an FBU whose source IP address is not the PCoA.

   If a Handover Acknowledge (HAck) message is not received as a
   response in a short time period (no less than twice the typical round
   trip time (RTT) between source and destination, or 100 milliseconds
   if RTT is not known), the Handover Initiate SHOULD be resent.
   Subsequent retransmissions can be up to HI_RETRIES, but MUST use
   exponential backoff in which the timeout period (i.e., 2xRTT or 100
   milliseconds) is doubled during each instance of retransmission.

6.2.1.2.  Handover Acknowledge (HAck)

   The Handover Acknowledge message is a new Mobility Header message
   that MUST be sent (typically by the NAR to the PAR) as a reply to the
   Handover Initiate message.

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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                     |           Sequence #          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Reserved   |      Code     |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               .
     |                                                               |
     .                                                               .
     .                          Mobility options                     .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 7: Handover Acknowledge (HAck) Message

      IP Fields:

         Source Address: Copied from the destination address of the
         Handover Initiate Message to which this message is a response.

         Destination Address: Copied from the source address of the
         Handover Initiate Message to which this message is a response.

         Sequence #: Copied from the corresponding field in the HI
         message to which this message is a response, to enable the
         receiver to match this HAck message with an outstanding HI
         message.

         Code:

            0: Handover Accepted, NCoA valid

            1: Handover Accepted, NCoA not valid or in use

            2: Handover Accepted, NCoA assigned (used in Assigned
            Addressing)

            3: Handover Accepted, use PCoA

            4: Message sent unsolicited, usually to trigger an HI
            message

            128: Handover Not Accepted, reason unspecified

            129: Administratively prohibited

            130: Insufficient resources

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         Reserved: MUST be set to zero by the sender and ignored by the
         receiver.

      Valid Options:

         New Care-of Address: If the 'S' flag in the Handover Initiate
         message is set, this option MUST be used to provide the NCoA
         that the MN should use when connected to this router.  This
         option MAY be included, even when the 'S' bit is not set, e.g.,
         Code 2 above.

   Upon receiving an HI message, the NAR MUST respond with a Handover
   Acknowledge message.  If the 'S' flag is set in the HI message, the
   NAR SHOULD include the New Care-of Address option and a Code 3.

   The NAR MAY provide support for the PCoA (instead of accepting or
   assigning an NCoA), establish a host route entry for the PCoA, and
   set up a tunnel to the PAR to forward the MN's packets sent with the
   PCoA as a source IP address.  This host route entry SHOULD be used to
   forward packets once the NAR detects that the particular MN is
   attached to its link.  The NAR indicates forwarding support for the
   PCoA using Code value 3 in the HAck message.  Subsequently, the PAR
   establishes a tunnel to the NAR in order to forward packets arriving
   for the PCoA.

   When responding to an HI message containing a Code value 1, the Code
   values 1, 2, and 4 in the HAck message are not relevant.

   Finally, the New Access Router can always refuse handover, in which
   case it MUST indicate the reason in one of the available Code values.

6.2.2.  Fast Binding Update (FBU)

   The Fast Binding Update message has a Mobility Header Type value of
   8.  The FBU is identical to the Mobile IPv6 Binding Update (BU)
   message.  However, the processing rules are slightly different.
   Furthermore, additional flags (as part of the Reserved field below)
   defined by other related protocols are not relevant in this message,
   and MUST be set to zero.

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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                     |           Sequence #          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |A|H|L|K|       Reserved        |            Lifetime           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                           Mobility options                    .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 8:  Fast Binding Update (FBU) Message

      IP Fields:

         Source Address: The PCoA or NCoA

         Destination Address: The IP address of the Previous Access
         Router

      'A' flag: MUST be set to one to request that PAR send a Fast
      Binding Acknowledgment message.

      'H' flag: MUST be set to one.  See [RFC3775].

      'L' flag: See [RFC3775].

      'K' flag: See [RFC3775].

      Reserved: This field is unused.  MUST be set to zero.

      Sequence Number: See [RFC3775].

      Lifetime: The requested time in seconds for which the sender
      wishes to have a binding.

      Mobility Options: MUST contain an alternate CoA option set to the
      NCoA when an FBU is sent from the PAR's link.  MUST contain the
      Binding Authorization Data for the FMIP (BADF) option.  See
      Section 6.4.5.  MAY contain the Mobility Header LLA option (see
      Section 6.4.4).

   The MN sends an FBU message any time after receiving a PrRtAdv
   message.  If the MN moves prior to receiving a PrRtAdv message, it
   SHOULD send an FBU to the PAR after configuring the NCoA on the NAR

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   according to Neighbor Discovery and IPv6 Address Configuration
   protocols.  When the MN moves without having received a PrRtAdv
   message, it cannot transmit an UNA message upon attaching to the
   NAR's link.

   The source IP address is the PCoA when the FBU is sent from the PAR's
   link, and the source IP address is the NCoA when the FBU sent from
   the NAR's link.  When the source IP address is the PCoA, the MN MUST
   include the alternate CoA option set to NCoA.  The PAR MUST process
   the FBU even though the address in the alternate CoA option is
   different from that in the source IP address, and ensure that the
   address in the alternate CoA option is used in the New CoA option in
   the HI message to the NAR.

   The FBU MUST also include the Home Address Option set to PCoA.  An
   FBU message MUST be protected so that the PAR is able to determine
   that the FBU message is sent by an MN that legitimately owns the
   PCoA.

6.2.3.  Fast Binding Acknowledgment (FBack)

   The FBack message format is identical to the Mobile IPv6 Binding
   Acknowledgment (BAck) message.  However, the processing rules are
   slightly different.  Furthermore, additional flags (as part of the
   Reserved field below) defined by other related protocols are not
   relevant in this message, and MUST be set to zero.

   The Fast Binding Acknowledgment message has a Mobility Header Type
   value of 9.  The FBack message is sent by the PAR to acknowledge
   receipt of a Fast Binding Update message in which the 'A' bit is set.
   If PAR sends an HI message to the NAR after processing an FBU, the
   FBack message SHOULD NOT be sent to the MN before the PAR receives a
   HAck message from the NAR.  The PAR MAY send the FBack immediately in
   the reactive mode, however.  The Fast Binding Acknowledgment MAY also
   be sent to the MN on the old link.

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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                     |     Status      |K|  Reserved |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Sequence #         |            Lifetime           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                           Mobility options                    .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 9: Fast Binding Acknowledgment (FBack) Message

      IP Fields:

         Source address: The IP address of the Previous Access Router

         Destination Address: The NCoA, and optionally the PCoA

      Status: 8-bit unsigned integer indicating the disposition of the
      Fast Binding Update.  Values of the Status field that are less
      than 128 indicate that the Binding Update was accepted by the
      receiving node.  The following such Status values are currently
      defined:

         0: Fast Binding Update accepted

         1: Fast Binding Update accepted but NCoA is invalid.  Use NCoA
         supplied in "alternate" CoA

      Values of the Status field greater than or equal to 128 indicate
      that the Binding Update was rejected by the receiving node.  The
      following such Status values are currently defined:

         128: Reason unspecified

         129: Administratively prohibited

         130: Insufficient resources

         131: Incorrect interface identifier length

      'K' flag: See [RFC3775].

      Reserved: An unused field.  MUST be set to zero.

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      Sequence Number: Copied from the FBU message for use by the MN in
      matching this acknowledgment with an outstanding FBU.

      Lifetime: The granted lifetime in seconds for which the sender of
      this message will retain a binding for traffic redirection.

      Mobility Options: MUST contain an "alternate" CoA if Status is 1.
      MUST contain the Binding Authorization Data for FMIP (BADF)
      option.  See Section 6.4.5.

6.3.  Unsolicited Neighbor Advertisement (UNA)

   This is the same message as in [RFC4861] with the requirement that
   the 'O' bit is always set to zero.  Since this is an unsolicited
   message, the 'S' bit is zero, and since this is sent by an MN, the
   'R' bit is also zero.

   If the NAR is proxying the NCoA (as a result of HI and HAck
   exchange), then UNA processing has additional steps (see below).  If
   the NAR is not proxying the NCoA (for instance, HI and HAck exchange
   has not taken place), then UNA processing follows the same procedure
   as specified in [RFC4861].  Implementations MAY retransmit UNAs
   subject to the specification in Section 7.2.6 of [RFC4861] while
   noting that the default RetransTimer value is large for handover
   purposes.

   The Source Address in UNA MUST be the NCoA.  The destination address
   is typically the all-nodes multicast address; however, some
   deployments may not prefer transmission to a multicast address.  In
   such cases, the destination address SHOULD be the NAR's IP address.

   The Target Address MUST include the NCoA, and the Target link-layer
   address MUST include the MN's LLA.

   The MN sends an UNA message to the NAR, as soon as it regains
   connectivity on the new link.  Arriving or buffered packets can be
   immediately forwarded.  If the NAR is proxying the NCoA, it creates a
   neighbor cache entry in STALE state but forwards packets as it
   determines bidirectional reachability according to the standard
   Neighbor Discovery procedure.  If there is an entry in INCOMPLETE
   state without a link-layer address, the NAR sets it to STALE, again
   according to the procedure in [RFC4861].

   The NAR MAY wish to provide a different IP address to the MN than the
   one in the UNA message.  In such a case, the NAR MUST delete the
   proxy entry for the NCoA and send a Router Advertisement with a NAACK
   option containing the new IP address.

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   The combination of the NCoA (present in the source IP address) and
   the Link-Layer Address (present as a Target LLA) SHOULD be used to
   distinguish the MN from other nodes.

6.4.  New Options

   All the options, with the exception of Binding Data Authorization for
   FMIPv6 (BADF) discussed in Section 6.4.5, use the Type, Length, and
   Option-Code format shown in Figure 10.

   The Type values are defined from the Neighbor Discovery options space
   and Mobility Header options space.  The Length field is in units of 8
   octets for Neighbor Discovery options, and is in units of octets for
   Mobility Header options.  And, Option-Code provides additional
   information for each of the options (see individual options below).

      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    |  Option-Code  |               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                                  ...                          ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 10: Option Format

6.4.1.  IP Address/Prefix Option

   This option is sent in the Proxy Router Advertisement 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |   Length      | Option-Code   | Prefix Length |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             Reserved                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                             IPv6 Address                      +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 11: IPv6 Address/Prefix Option

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      Type: 17

      Length: The size of this option in 8 octets including the Type,
      Option-Code, and Length fields.

      Option-Code:

         1: Old Care-of Address

         2: New Care-of Address

         3: NAR's IP address

         4: NAR's Prefix, sent in PrRtAdv.  The Prefix Length field
         contains the number of valid leading bits in the prefix.  The
         bits in the prefix after the prefix length are reserved and
         MUST be initialized to zero by the sender and ignored by the
         receiver.

      Prefix Length: 8-bit unsigned integer that indicates the length of
      the IPv6 Address Prefix.  The value ranges from 0 to 128.

      Reserved: MUST be set to zero by the sender and MUST be ignored by
      the receiver.

      IPv6 address: The IP address defined by the Option-Code field.

6.4.2.  Mobility Header IP Address/Prefix Option

   This option is sent in the Handover Initiate and Handover Acknowledge
   messages.  This option has an alignment requirement of 8n+4.

      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      | Option-Code   | Prefix Length |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                    IPv6 Address/Prefix                        +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 12: Mobility Header IPv6 Address/Prefix Option

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      Type: 17

      Length: The size of this option in octets excluding the Type and
      Length fields.

      Option-Code:

         1: Old Care-of Address

         2: New Care-of Address

         3: NAR's IP address

         4: NAR's Prefix, sent in PrRtAdv.  The Prefix Length field
         contains the number of valid leading bits in the prefix.  The
         bits in the prefix after the prefix length are reserved and
         MUST be initialized to zero by the sender and ignored by the
         receiver.

      Prefix Length: 8-bit unsigned integer that indicates the length of
      the IPv6 Address Prefix.  The value ranges from 0 to 128.

      IPv6 address/prefix: The IP address/prefix defined by the Option-
      Code field.

6.4.3.  Link-Layer Address (LLA) Option

      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     |  Option-Code  |       LLA...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 13: Link-Layer Address Option

      Type: 19

      Length: The size of this option in 8 octets including the Type,
      Option-Code, and Length fields.

      Option-Code:

         0: Wildcard requesting resolution for all nearby access points

         1: Link-Layer Address of the New Access Point

         2: Link-Layer Address of the MN

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         3: Link-Layer Address of the NAR (i.e., Proxied Originator)

         4: Link-Layer Address of the source of RtSolPr or PrRtAdv
         message

         5: The access point identified by the LLA belongs to the
         current interface of the router

         6: No prefix information available for the access point
         identified by the LLA

         7: No fast handover support available for the access point
         identified by the LLA

      LLA: The variable-length link-layer address.

   The LLA option does not have a length field for the LLA itself.  The
   implementations must consult the specific link layer over which the
   protocol is run in order to determine the content and length of the
   LLA.

   Depending on the size of individual LLA option, appropriate padding
   MUST be used to ensure that the entire option size is a multiple of 8
   octets.

   The New Access Point Link-Layer Address contains the link-layer
   address of the access point for which handover is about to be
   attempted.  This is used in the Router Solicitation for Proxy
   Advertisement message.

   The MN Link-Layer Address option contains the link-layer address of
   an MN.  It is used in the Handover Initiate message.

   The NAR (i.e., Proxied Originator) Link-Layer Address option contains
   the link-layer address of the access router to which the Proxy Router
   Solicitation message refers.

6.4.4.  Mobility Header Link-Layer Address (MH-LLA) Option

   This option is identical to the LLA option, but is carried in the
   Mobility Header messages, e.g., FBU.  In the future, other Mobility
   Header messages may also make use of this option.  The format of the
   option is shown in Figure 14.  There are no alignment requirements
   for this option.

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       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    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Option-Code   |                  LLA                     ....
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 14: Mobility Header Link-Layer Address Option

      Type: 7

      Length: The size of this option in octets not including the Type
      and Length fields.

      Option-Code: 2   Link-Layer Address of the MN.

      LLA: The variable-length link-layer address.

6.4.5.  Binding Authorization Data for FMIPv6 (BADF)

   This option MUST be present in FBU and FBack messages.  The security
   association between the MN and the PAR is established by companion
   protocols [RFC5269].  This option specifies how to compute and verify
   a Message Authentication Code (MAC) using the established security
   association.

   The format of this option is shown in Figure 15.

        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      | Option Length |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            SPI                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                         Authenticator                         |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 15: Binding Authorization Data for FMIPv6 (BADF) Option

      Type: 21

      Option Length: The length of the Authenticator in bytes

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      SPI: Security Parameter Index.  SPI = 0 is reserved for the
      Authenticator computed using SEND-based handover keys.

      Authenticator: Same as in RFC 3775, with "correspondent" replaced
      by the PAR's IP address, and Kbm (binding management key) replaced
      by the shared key between the MN and the PAR.

   The default MAC calculation is done using HMAC_SHA1 with the first 96
   bits used for the MAC.  Since there is an Option Length field,
   implementations can use other algorithms such as HMAC_SHA256.

   This option MUST be the last Mobility Option present.

6.4.6.  Neighbor Advertisement Acknowledgment (NAACK)

      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    | Option-Code   |    Status     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             Reserved                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 16: Neighbor Advertisement Acknowledgment Option

      Type: 20

      Length: 8-bit unsigned integer.  Length of the option, in 8
      octets.  The length is 1 when a new CoA is not supplied.  The
      length is 3 when a new CoA is present (immediately following the
      Reserved field)

      Option-Code: 0

      Status: 8-bit unsigned integer indicating the disposition of the
      Unsolicited Neighbor Advertisement message.  The following Status
      values are currently defined:

         1: NCoA is invalid, perform address configuration

         2: NCoA is invalid, use the supplied NCoA.  The supplied NCoA
         (in the form of an IP Address Option) MUST be present following
         the Reserved field.

         3: NCoA is invalid, use NAR's IP address as NCoA in FBU

         4: PCoA supplied, do not send FBU

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         128: Link-Layer Address unrecognized

      Reserved: MUST be set to zero by the sender and MUST be ignored by
      the receiver.

   The NAR responds to an UNA with the NAACK option to notify the MN to
   use a different NCoA than the one that the MN has used.  If the NAR
   proposes a different NCoA, the Router Advertisement MUST use the
   source IP address in the UNA message as the destination address, and
   use the L2 address present in UNA.  The MN MUST use the NCoA if it is
   supplied with the NAACK option.  If the NAACK indicates that the
   Link-Layer Address is unrecognized (for instance, if the MN uses an
   LLA valid on PAR's link but the same LLA is not valid on NAR's link
   due to a different access technology), the MN MUST NOT use the NCoA
   or the PCoA and SHOULD start immediately the process of acquiring a
   different NCoA at the NAR.

   In the future, new option types may be defined.



(page 40 continued on part 3)

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