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rfc:rfc1953

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

Newman, et. al. Informational [Page 1] RFC 1953 IFMP Specification May 1996

     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.

Newman, et. al. Informational [Page 2] RFC 1953 IFMP Specification May 1996

 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:

Newman, et. al. Informational [Page 3] RFC 1953 IFMP Specification May 1996

     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.

Newman, et. al. Informational [Page 4] RFC 1953 IFMP Specification May 1996

 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).

Newman, et. al. Informational [Page 5] RFC 1953 IFMP Specification May 1996

 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.

Newman, et. al. Informational [Page 6] RFC 1953 IFMP Specification May 1996

 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.

Newman, et. al. Informational [Page 7] RFC 1953 IFMP Specification May 1996

      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.

Newman, et. al. Informational [Page 8] RFC 1953 IFMP Specification May 1996

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.

Newman, et. al. Informational [Page 9] RFC 1953 IFMP Specification May 1996

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

Newman, et. al. Informational [Page 10] RFC 1953 IFMP Specification May 1996

           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.

Newman, et. al. Informational [Page 11] RFC 1953 IFMP Specification May 1996

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.

Newman, et. al. Informational [Page 12] RFC 1953 IFMP Specification May 1996

 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.

Newman, et. al. Informational [Page 13] RFC 1953 IFMP Specification May 1996

 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.

Newman, et. al. Informational [Page 14] RFC 1953 IFMP Specification May 1996

 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.

Newman, et. al. Informational [Page 15] RFC 1953 IFMP Specification May 1996

 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:

Newman, et. al. Informational [Page 16] RFC 1953 IFMP Specification May 1996

  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.

Newman, et. al. Informational [Page 17] RFC 1953 IFMP Specification May 1996

 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.

Newman, et. al. Informational [Page 18] RFC 1953 IFMP Specification May 1996

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

Newman, et. al. Informational [Page 19] RFC 1953 IFMP Specification May 1996

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

Newman, et. al. Informational [Page 20]

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