





Network Working Group                                 P. Newman, Ipsilon
Request for Comments: 1953                         W. L. Edwards, Sprint
Category: Informational                               R. Hinden, Ipsilon
                                                     E. Hoffman, Ipsilon
                                                  F. Ching Liaw, Ipsilon
                                                        T. Lyon, Ipsilon
                                                    G. Minshall, Ipsilon
                                                                May 1996


        Ipsilon Flow Management Protocol Specification for IPv4
                              Version 1.0

Status of this Memo

   This document provides information for the Internet community.  This
   memo does not specify an Internet standard of any kind.  Distribution
   of this memo is unlimited.

IESG Note:

   This memo documents a private protocol for IPv4-based flows.  This
   protocol is NOT the product of an IETF working group nor is it a
   standards track document.  It has not necessarily benefited from the
   widespread and in depth community review that standards track
   documents receive.

Abstract

   The Ipsilon Flow Management Protocol (IFMP), is a protocol for
   allowing a node to instruct an adjacent node to attach a layer 2
   label to a specified IP flow.  The label allows more efficient access
   to cached routing information for that flow.  The label can also
   enable a node to switch further packets belonging to the specified
   flow at layer 2 rather than forwarding them at layer 3.

Table of Contents

   1. Introduction....................................................2
   2. Flow Types......................................................2
   3. IFMP Adjacency Protocol.........................................4
       3.1  Packet Format.............................................4
       3.2  Procedure.................................................7
   4. IFMP Redirection Protocol......................................10
       4.1  Redirect Message.........................................12
       4.2  Reclaim Message..........................................13
       4.3  Reclaim Ack Message......................................15
       4.4  Label Range Message......................................16



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       4.5  Error Message............................................17
   References........................................................19
   Security Considerations...........................................19
   Authors' Addresses................................................19

1. Introduction

   The Ipsilon Flow Management Protocol (IFMP), is a protocol for
   instructing an adjacent node to attach a layer 2 label to a specified
   IP flow. The label allows more efficient access to cached routing
   information for that flow and it allows the flow to be switched
   rather than routed in certain cases.

   If a network node's upstream and downstream links both redirect a
   flow at the node, then the node can switch the flow at the data link
   layer rather than forwarding it at the network layer.  The label
   space is managed at the downstream end of each link and redirection
   messages are sent upstream to associate a particular flow with a
   given label.  Each direction of transmission on a link is treated
   separately.

   If the flow is not refreshed by the time the lifetime field in the
   redirect message expires, then the association between the flow and
   the label is discarded.  A flow is refreshed by sending a redirect
   message, identical to the original, before the lifetime expires.

   Several flow types may be specified.  Each flow type specifies the
   set of fields from the packet header that are used to identify a
   flow.  There must be an ordering amongst the different flow types
   such that a most specific match operation may be performed.

   A particular flow is specified by a flow identifier.  The flow
   identifier for that flow gives the contents of the set of fields from
   the packet header as defined for the flow type to which it belongs.

   This document specifies the IFMP protocol for IPv4 on a point-to-
   point link.  The definition of labels, and the encapsulation of
   flows, are specified in a separate document for each specific data
   link technology.  The specification for ATM data links is given in
   [ENCAP].

2. Flow Types

   A flow is a sequence of packets that are sent from a particular
   source to a particular (unicast or multicast) destination and that
   are related in terms of their routing and any logical handling policy
   they may require.




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   A flow is identified by its flow identifier.

   Several different flow types can be defined.  The particular set of
   fields from the packet header used to identify a flow constitutes the
   flow type.  The values of these fields, for a particular flow,
   constitutes the flow identifier for that flow.  The values of these
   fields must be invariant in all packets belonging to the same flow at
   any point in the network.

   Flow types are sub- or super-sets of each other such that there is a
   clear hierarchy of flow types.  This permits a most specific match
   operation to be performed.  (If additional flow types are defined in
   the future that are not fully ordered then the required behavior will
   be defined.) Each flow type also specifies an encapsulation that is
   to be used after a flow of this type is redirected.  The
   encapsulations for each flow type are specified in a separate
   document for each specific data link technology.  The encapsulations
   for flows over ATM data links are given in [ENCAP].

   Three flow types are defined in this version of the protocol:

   Flow Type 0

      Flow Type 0 is used to change the encapsulation of IPv4 packets
      from the default encapsulation.

      For Flow Type 0: Flow Type = 0 and Flow ID Length = 0.

      The Flow Identifier for Flow Type 0 is null (zero length).

   Flow Type 1

      Flow Type 1 is designed for protocols such as UDP and TCP in which
      the first four octets after the IPv4 header specify a Source Port
      number and a Destination Port number.

      For Flow Type 1, Flow Type = 1 and Flow ID Length = 4 (32 bit
      words).

      The format of the Flow Identifier for Flow Type 1 is:











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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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Version|  IHL  |Type of Service| Time to Live  |   Protocol    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Source Address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Destination Address                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Source Port          |       Destination Port        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Flow Type 2

      For Flow Type 2, Flow Type = 2 and Flow ID Length = 3 (32 bit
      words).

      The format of the Flow Identifier for Flow Type 2 is:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Version|  IHL  |   Reserved    | Time to Live  |   Reserved    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Source Address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Destination Address                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      The Reserved fields are unused and should be set to zero by the
      sender and ignored by the receiver.

3. IFMP Adjacency Protocol

   The IFMP Adjacency Protocol allows a host or router to discover the
   identity of a peer at the other end of a link.  It is also used to
   synchronize state across the link, to detect when the peer at the
   other end of the link changes, and to exchange a list of IP addresses
   assigned to the link.

3.1 Packet Format

   All IFMP messages belonging to the Adjacency Protocol must be
   encapsulated within an IPv4 packet and must be sent to the IP limited
   broadcast address (255.255.255.255).  The Protocol field in the IP
   header must contain the value 101 (decimal) indicating that the IP
   packet contains an IFMP message.  The Time to Live (TTL) field in the
   IP header must be set to 1.



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   All IFMP messages belonging to the adjacency protocol have the
   following structure:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Version    |    Op Code    |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sender Instance                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Peer Instance                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Peer Identity                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Peer Next Sequence Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Reserved              |    Reserved   | Max Ack Intvl |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                          Address List                         ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Version
             The IFMP protocol version number.  The current Version = 1.

   Op Code
             Specifies the function of the message.  Four Op Codes are
             defined for the IFMP Adjacency Protocol:

                SYN:    Op Code = 0
                SYNACK: Op Code = 1
                RSTACK: Op Code = 2
                ACK:    Op Code = 3

   Checksum
             The 16-bit one's complement of the one's complement sum of
             a pseudo header of information from the IP header and the
             IFMP message itself.  The pseudo header, conceptually
             prefixed to the IFMP message, contains the Source Address,
             the Destination Address, and the Protocol fields from the
             IPv4 header, and the total length of the IFMP message
             starting with the Version field (this is equivalent to the
             value of the Total Length field from the IPv4 header minus
             the length of the IPv4 header itself).






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   Sender Instance
             For the SYN, SYNACK, and ACK messages, is the sender's
             instance number for the link.  The receiver uses this to
             detect when the link comes back up after going down or when
             the identity of the peer at the other end of the link
             changes.  The instance number is a 32 bit number that is
             guaranteed to be unique within the recent past and to
             change when the link or node comes back up after going
             down.  It is used in a similar manner to the initial
             sequence number (ISN) in TCP [RFC 793].  Zero is not a
             valid instance number.  For the RSTACK message the Sender
             Instance field is set to the value of the Peer Instance
             field from the incoming message that caused an RSTACK
             message to be generated.

   Peer Instance
             For the SYN, SYNACK, and ACK messages, is what the sender
             believes is the peer's current instance number for the
             link.  If the sender of the message does not know the
             peer's current instance number for the link, the sender
             must set this field to zero.  For the RSTACK message the
             Peer Instance field is set to the value of the Sender
             Instance field from the incoming message that caused an
             RSTACK message to be generated.

   Peer Identity
             For the SYN, SYNACK, and ACK messages, is the IP address of
             the peer that the sender of the message believes is at the
             other end of the link.  The Peer Identity is taken from the
             Source IP Address of the IP header of a SYN or a SYNACK
             message.  If the sender of the message does not know the IP
             address of the peer at the other end of the link, the
             sender must set set this field to zero.  For the RSTACK
             message, the Peer Identity field is set to the value of the
             Source Address field from the IP header of the incoming
             message that caused an RSTACK message to be generated.

   Peer Next Sequence Number
             Gives the value of the peer's Sequence Number that the
             sender of the IFMP Adjacency Protocol message expects to
             arrive in the next IFMP Redirection Protocol message.  If a
             node is in the ESTAB state, and the value of the Peer Next
             Sequence Number in an incoming ACK message is greater than
             the value of the Sequence Number plus one, from the last
             IFMP Redirection Protocol message transmitted out of the
             port on which the incoming ACK message was received, the
             link should be reset.  The procedure to reset the link is
             defined in section 3.2.



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   Max Ack Intvl
             Maximum Acknowledgement Interval is the maximum amount of
             time the sender of the message will wait until transmitting
             an ACK message.

   Address List
             A list of one or more IP addresses that are assigned to the
             link by the sender of the message.  The list must have at
             least one entry that is identical to the Source Address in
             the IP header.  The contents of this list are not used by
             the IFMP protocol but can be made available to the routing
             protocol.

3.2 Procedure

   The IFMP Adjacency Protocol is described by the rules and state
   tables given in this section.

   The rules and state tables use the following operations:

    o The "Update Peer Verifier" operation is defined as storing the
      Sender Instance and the Source IP Address from a SYN or SYNACK
      message received from the peer on a particular port.

    o The procedure "Reset the link" is defined as:

          1. Generate a new instance number for the link
          2. Delete the peer verifier (set the stored values of Sender
             Instance and Source IP Address of the peer to zero)
          3. Set Sequence Number and Peer Next Sequence Number to zero
          4. Send a SYN message
          5. Enter the SYNSENT state

    o The state tables use the following Boolean terms and operators:

        A    The Sender Instance in the incoming message matches the
             value stored from a previous message by the "Update Peer
             Verifier" operation for the port on which the incoming
             message is received.

        B    The Sender Instance and the Source IP Address in the
             incoming message matches the value stored from a previous
             message by the "Update Peer Verifier" operation for the
             port on which the incoming message is received.







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        C    The Peer Instance and Peer Identity in the incoming message
             matches the value of the Sender Instance and the Source IP
             Address currently in use for all SYN, SYNACK, and ACK
             messages transmitted out of the port on which the incoming
             message was received.

        "&&" Represents the logical AND operation

        "||" Represents the logical OR operation

        "!" Represents the logical negation (NOT) operation.

    o A timer is required for the periodic generation of SYN, SYNACK,
      and ACK messages.  The period of the timer is unspecified but a
      value of one second is suggested.

      There are two independent events: the timer expires, and a packet
      arrives.  The processing rules for these events are:

         Timer Expires:   Reset Timer
                          If state = SYNSENT Send SYN
                          If state = SYNRCVD Send SYNACK
                          If state = ESTAB   Send ACK

         Packet Arrives:  If incoming message is an RSTACK
                             If A && C && !SYNSENT
                                Reset the link
                             Else Discard the message
                          Else the following State Tables.


    o State synchronization across a link is considered to be achieved
      when a node reaches the ESTAB state.


















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State Tables

   State: SYNSENT

+======================================================================+
|     Condition      |                Action               | New State |
+====================+=====================================+===========+
|    SYNACK && C     |  Update Peer Verifier; Send ACK     |   ESTAB   |
+--------------------+-------------------------------------+-----------+
|    SYNACK && !C    |            Send RSTACK              |  SYNSENT  |
+--------------------+-------------------------------------+-----------+
|        SYN         |  Update Peer Verifier; Send SYNACK  |  SYNRCVD  |
+--------------------+-------------------------------------+-----------+
|        ACK         |            Send RSTACK              |  SYNSENT  |
+======================================================================+

   State: SYNRCVD

+======================================================================+
|     Condition      |                Action               | New State |
+====================+=====================================+===========+
|    SYNACK && C     |  Update Peer Verifier; Send ACK     |   ESTAB   |
+--------------------+-------------------------------------+-----------+
|    SYNACK && !C    |            Send RSTACK              |  SYNRCVD  |
+--------------------+-------------------------------------+-----------+
|        SYN         |  Update Peer Verifier; Send SYNACK  |  SYNRCVD  |
+--------------------+-------------------------------------+-----------+
|    ACK && B && C   |              Send ACK               |   ESTAB   |
+--------------------+-------------------------------------+-----------+
|  ACK && !(B && C)  |            Send RSTACK              |  SYNRCVD  |
+======================================================================+

   State: ESTAB

+=======================================================================+
|     Condition       |                Action               | New State |
+=====================+=====================================+===========+
|   SYN || SYNACK     |            Send ACK (note 1)        |   ESTAB   |
+---------------------+-------------------------------------+-----------+
|   ACK && B && C     |            Send ACK (note 1)        |   ESTAB   |
+---------------------+-------------------------------------+-----------+
|  ACK && !(B && C)   |              Send RSTACK            |   ESTAB   |
+=======================================================================+


 Note 1: No more than one ACK should be sent within any time period of
        length defined by the timer.




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4. IFMP Redirection Protocol

   A sender encapsulates within an IPv4 packet all IFMP messages
   belonging to the Redirection Protocol.  The sender sends these
   messages to the unicast IP address of the peer at the other end of
   the link. The IP address of the peer is obtained from the adjacency
   protocol.  The Protocol field in the IP header must contain the value
   101 (decimal) indicating that the IP packet contains an IFMP message.
   The Time to Live (TTL) field in the IP header must be set to 1.

   All IFMP Redirection Protocol messages have the following structure:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Version    |    Op Code    |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sender Instance                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Peer Instance                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                          Message Body                         ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Version
             The IFMP protocol version number, currently Version = 1.

   Op Code
             This field gives the message type.  Five message types are
             currently defined for the IFMP Redirection Protocol:

                 REDIRECT:     Op Code = 4
                 RECLAIM:      Op Code = 5
                 RECLAIM ACK:  Op Code = 6
                 LABEL RANGE:  Op Code = 7
                 ERROR:        Op Code = 8

   Checksum
             The 16-bit one's complement of the one's complement sum of
             a pseudo header of information from the IP header, and the
             IFMP message itself.  The pseudo header, conceptually
             prefixed to the IFMP message, contains the Source Address,
             the Destination Address, and the Protocol fields from the



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             IPv4 header, and the total length of the IFMP message
             starting with the version field (this is equivalent to the
             value of the Total Length field from the IPv4 header minus
             the length of the IPv4 header itself).

   Sender Instance
             The sender's instance number for the link from the IFMP
             Adjacency Protocol.

   Peer Instance
             What the sender believes is the peer's current instance
             number for the link from the IFMP Adjacency protocol.

   Sequence Number
             The sender must increment by one, modulo 2**32, for every
             IFMP Redirection Protocol message sent across a link.  It
             allows the receiver to process IFMP Redirection Protocol
             messages in order.  The Sequence Number is set to zero when
             a node resets the link.

   Message Body
             Contains a list of one or more IFMP Redirection Protocol
             message elements.  All of the message elements in the list
             have the same message type because the Op Code field
             applies to the entire IFMP message.  The number of message
             elements included in a single packet must not cause the
             total size of the IFMP message to exceed the MTU size of
             the underlying data link.  Only a single message element is
             permitted in a Label Range message or in an Error message.

   No IFMP Redirection Protocol messages can be sent across a link until
   the IFMP Adjacency Protocol has achieved state synchronization across
   that link.  All IFMP Redirection Protocol messages received on a link
   that does not currently have state synchronization must be discarded.
   For every received IFMP Redirection Protocol message the receiver
   must check the Source IP Address from the IP header, the Sender
   Instance, and the Peer Instance.  The incoming message must be
   discarded if the Sender Instance and the Source IP Address fields do
   not match the values stored by the "Update Peer Verifier" operation
   of the IFMP Adjacency Protocol for the port on which the message is
   received.  The incoming message must also be discarded if the Peer
   Instance field does not match the current value for the Sender
   Instance of the IFMP Adjacency Protocol.








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4.1 Redirect Message

   The Redirect Message element is used to instruct an adjacent node to
   attach one or more given labels to packets belonging to one or more
   specified flows each for a specified period of time.  The Redirect
   message is not acknowledged.

   Each Redirect message element has the following structure:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Flow Type   | Flow ID Length|           Lifetime            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Label                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                         Flow Identifier                       ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Flow Type
             Specifies the Flow Type of the flow identifier contained in
             the Flow Identifier field.

   Flow ID Length
             Specifies the length of the Flow Identifier field in
             integer multiples of 32 bit words.

   Lifetime field
             Specifies the length of time, in seconds, for which this
             redirection is valid.  The association of flow identifier
             and label should be discarded at a time no greater than
             that specified by the Lifetime field.  A value of zero is
             not valid.

   Label field
             Contains a 32 bit label.  The format of the label is
             dependent upon the type of physical link across which the
             Redirect message is sent.  (The format of the label for ATM
             data links is specified in [ENCAP].)

   Flow Identifier
             Identifies the flow with which the specified label should
             be associated.  The length of the Flow Identifier field
             must be an integer multiple of 32 bit words to preserve 32
             bit alignment.



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   A node can send an IFMP message containing one or more Redirect
   message elements across a link to its upstream neighbor.  Each
   Redirect message element requests that the upstream neighbor
   associate a given link-level label to packets belonging to a
   specified flow for up to a specified period of time.  A node
   receiving an IFMP message that contains one or more Redirect message
   elements from an adjacent downstream neighbor can choose to ignore
   any or all of the Redirect message elements.  Neither the IFMP
   message nor any of the Redirect message elements are acknowledged.
   If the node chooses to accept a particular Redirect message element
   and to redirect the specified flow, it should attach the label
   specified in the Redirect message element to all further packets sent
   on that flow until it chooses to do so no longer, or until the
   specified lifetime expires.  While the flow remains redirected, the
   encapsulation specified by the definition of the Flow Type given in
   the Redirect message element must be used for all packets belonging
   to that flow.  If the label in a Redirect message element is outside
   the range that can be handled across the relevant link, a Label Range
   message can be returned to the sender.  The Label Range message
   informs the sender of the Redirect message of the range of labels
   that can be sent across the link.

   If a Redirect message element is received specifying a flow that is
   already redirected, the Label field in the received Redirect message
   element must be checked against the label stored for the redirected
   flow.  If they agree, the lifetime of the redirected flow is reset to
   that contained in the Redirect message element.  If they disagree,
   the Redirect message element is ignored, and the flow returned to the
   default state.  There is a minimum time between Redirect message
   elements specifying the same flow.  The default value is one second.

   If a receiving node detects an error in any of the fields of a
   Redirect message element, the node must discard that message element
   without affecting any other Redirect message elements in the same
   IFMP message.  The receiver should return an error message to the
   sender only in the case that the receiver does not understand the
   version of the IFMP protocol in the received IFMP message or does not
   understand a Flow Type in any of the Redirect message elements.  An
   Error Message should be returned for each Flow Type that is not
   understood.

4.2 Reclaim Message

   The Reclaim message element is used by a node to instruct an adjacent
   upstream node to unbind one or more flows from the labels to which
   they are currently bound, and to release the labels.





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   Each Reclaim message element has the following structure:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Flow Type   | Flow ID Length|           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Label                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                         Flow Identifier                       ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Flow Type
             Specifies the Flow Type of the Flow Identifier contained in
             the Flow ID field.

   Flow ID Length
             Specifies the length of the Flow Identifier field in
             integer multiples of 32 bit words.

   Reserved
             Field is unused and should be set to zero by the sender and
             ignored by the receiver.

   Label
             Field contains the label to be released.

   Flow Identifier
             Field contains the flow identifier to be unbound.

   A node can send a Reclaim message element to instruct an adjacent
   upstream node to unbind a flow from the label to which it is
   currently bound, return the flow to the default forwarding state, and
   release the label.  Each Reclaim message element applies to a single
   flow and a single label.  When the receiver has completed the
   operation, it must issue a Reclaim Ack message element.  Reclaim Ack
   message elements can be grouped together, in any order, into one or
   more IFMP Reclaim Ack messages and returned to the sender as an
   acknowledgment that the operation is complete.

   If a Reclaim message element is received indicating an unknown flow,
   a Reclaim Ack message element must be returned containing the same
   Label and Flow Identifier fields from the Reclaim message.





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   If a Reclaim message element is received indicating a known flow, but
   with a Label that is not currently bound to that flow, the flow must
   be unbound and returned to the default forwarding state, and a
   Reclaim Ack message sent containing the actual label to which the
   flow was previously bound.

   If the receiver detects an error in any of the fields of a Reclaim
   message element, the receiver must discard that message element,
   without affecting any other Reclaim message elements in the same
   message.  The receiver must return an error message to the sender
   only in the case that the receiver does not understand the version of
   the IFMP protocol in the received message or does not understand a
   Flow Type in one of the Reclaim message elements.

4.3 Reclaim Ack Message

   The Reclaim Ack message element is used by a receiving node to
   acknowledge the successful release of one or more reclaimed labels.

   Each Reclaim Ack message element has the following structure:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Flow Type   | Flow ID Length|           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Label                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                         Flow Identifier                       ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Flow Type
             Specifies the Flow Type of the Flow Identifier contained in
             the Flow Identifier field.

   Flow ID Length
             Specifies the length of the Flow Identifier field in
             integer multiples of 32 bit words.

   Reserved
             Field is unused and should be set to zero by the sender and
             ignored by the receiver.

   Label
             Field contains the label released from the flow specified
             by the Flow Identifier.



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   Flow Identifier
             Field contains the Flow Identifier from the Reclaim message
             element that requested the release of the label specified
             in the Label field.

   A Reclaim Ack message element must be sent in response to each
   Reclaim message element received.  It is sent to indicate that the
   requested flow is now unbound and that the label is now free.  If
   possible, each Reclaim Ack message element should not be sent until
   all data queued for transmission on the link, using the label
   specified for release, has been sent.

   If a Reclaim Ack message element is received specifying a flow for
   which no Reclaim message element was issued, that Reclaim Ack message
   element must be ignored, but no other Reclaim Ack message elements in
   the same message must be affected.

   If a Reclaim Ack message element is received specifying a different
   label from the one sent in the original Reclaim message element for
   that flow, the Reclaim Ack message element should be handled as if
   the reclaim operation were successful.

   If an error is detected in any of the fields of a Reclaim Ack message
   element, that message element must be discarded, but no other Reclaim
   Ack message elements in the same message must be affected.

   The receiver should return an Error message to the sender only in the
   case that the receiver does not understand the version of the IFMP
   protocol in the received message or does not understand a Flow Type
   in one of the Reclaim Ack message elements.

4.4 Label Range Message

   The Label Range message element is sent in response to a Redirect
   message if the label requested in one or more of the Redirect message
   elements is outside the range that the receiver of the Redirect
   message can handle.  The Label Range message informs the sender of
   the Redirect message of the label range that can be handled on the
   relevant link.

   Only a single Label Range message element is permitted in a Label
   Range message.  The Label Range message element has the following
   structure:








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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Minimum Label                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Maximum Label                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Minimum Label
             The minimum value of label that can be specified in an IFMP
             Redirection Protocol message across this link.

   Maximum Label
             The maximum value of label that can be specified in an IFMP
             Redirection Protocol message across this link.

   All values of label within the range Minimum Label to Maximum Label
   inclusive may be specified in an IFMP Redirection Protocol message
   across the link.

4.5 Error Message

   An Error message can be sent by a node in response to any IFMP
   Redirection Protocol message.

   Only a single Error message element is permitted in an Error message.
   The Error message element has the following structure:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Error Code   |                  Parameter                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Error Code
             Specifies which an error has occurred.

   Each Error message can specify a single Parameter.











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   Two Error message elements are specified:


   Bad Version:

   Error Code = 1. The sender of the Error message cannot process the
             version of the IFMP protocol of the message that caused the
             error.  This message must only be sent if the version of
             the message that caused the error is greater than the most
             recent version that the sender of the Error message can
             process.  The parameter field of this Error message gives
             the most recent version of the IFMP protocol that the
             sender can process, right justified, with the unused most
             significant bits of the Parameter field set to zero.

   Bad Flow Type:

   Error Code = 2. The sender of the Error message does not understand a
             Flow Type that was received in the message that caused the
             error.  The Flow Type that caused the error is given in the
             parameter field, right justified, with the unused most
             significant bits of the Parameter field set to zero.





























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REFERENCES

      [ENCAP] Newman, P., et. al., "Transmission of Flow Labelled IPv4
               on ATM Data Links Ipsilon Version 1.0," Ipsilon Networks,
               RFC 1954, May 1996.

      [RFC793] Postel, J., "Transmission Control Protocol," STD 7, RFC
               793, September 1981.

SECURITY CONSIDERATIONS

   Security issues are not discussed in this memo.

AUTHORS' ADDRESSES

   Peter Newman                        Phone: +1 (415) 846-4603
   Ipsilon Networks, Inc.              EMail: pn@ipsilon.com

   W. L. Edwards, Chief Scientist      Phone:  +1 (913) 534 5334
   Sprint                              EMail:  texas@sprintcorp.com

   Robert M. Hinden                    Phone: +1 (415) 846-4604
   Ipsilon Networks, Inc.              EMail: hinden@ipsilon.com

   Eric Hoffman                        Phone: +1 (415) 846-4610
   Ipsilon Networks, Inc.              EMail: hoffman@ipsilon.com

   Fong Ching Liaw                     Phone: +1 (415) 846-4607
   Ipsilon Networks, Inc.              EMail: fong@ipsilon.com

   Tom Lyon                            Phone: +1 (415) 846-4601
   Ipsilon Networks, Inc.              EMail: pugs@ipsilon.com

   Greg Minshall                       Phone: +1 (415) 846-4605
   Ipsilon Networks, Inc.              EMail: minshall@ipsilon.com
















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Ipsilon Networks, Inc. is located at:

   2191 East Bayshore Road
   Suite 100
   Palo Alto, CA 94303
   USA

Sprint is located at:

   Sprint
   Sprint Technology Services - Long Distance Division
   9300 Metcalf Avenue
   Mailstop KSOPKB0802
   Overland Park, KS 66212-6333
   USA




































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