RFC1953 - Ipsilon Flow Management Protocol Specification for IPv4 Version 1.0

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　　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

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.

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:

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.

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).

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 [RFC793]. 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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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:

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.

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.

REFERENCES

[ENCAP] Newman, P., et. al., "Transmission of Flow Labelled IPv4
on ATM Data Links Ipsilon Version 1.0," Ipsilon Networks,
RFC1954, 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

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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