Network Working Group                                    Tom Worster
INTERNET DRAFT                                     Ennovate Networks
Standards Track                                  Expires June 24 2000



        GSMP Packet Encapsulations for ATM, Ethernet and TCP

                     <draft-ietf-gsmp-encaps-00.txt>



  This document is an Internet-Draft and is in full conformance with
  all provisions of Section 10 of RFC2026.

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Abstract

  This memo specifies the encapsulation of GSMP packets in ATM,
  Ethernet and TCP.








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1. Introduction

  GSMP packets are defined in [1] and may be encapsulated in several
  different protocols for transport. This memo specifies their
  encapsulation in ATM AAL-5, in Ethernet or in TCP. Other
  encapsulations may be defined elsewhere.


2. ATM Encapsulation

  GSMP packets are variable length and for an ATM data link layer
  they are encapsulated directly in an AAL-5 CPCS-PDU [3] with an
  LLC/SNAP header as illustrated:

    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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               LLC (0xAA-AA-03)                |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
   |                   SNAP (0x00-00-00-88-0C)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                         GSMP Message                          ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Pad (0 - 47 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +            AAL-5 CPCS-PDU Trailer (8 octets)                  +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  (The convention in the documentation of Internet Protocols [4] is
  to express numbers in decimal. Numbers in hexadecimal format are
  specified by prefacing them with the characters "0x". Numbers in
  binary format are specified by prefacing them with the characters
  "0b". Data is pictured in "big-endian" order. That is, fields are
  described left to right, with the most significant octet on the
  left and the least significant octet on the right. Whenever a
  diagram shows a group of octets, the order of transmission of
  those octets is the normal order in which they are read in
  English. Whenever an octet represents a numeric quantity the left
  most bit in the diagram is the high order or most significant bit.
  That is, the bit labelled 0 is the most significant bit.
  Similarly, whenever a multi-octet field represents a numeric


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  quantity the left most bit of the whole field is the most
  significant bit. When a multi-octet quantity is transmitted, the
  most significant octet is transmitted first. This is the same
  coding convention as is used in the ATM layer [1] and AAL-5 [3].)

  The LLC/SNAP header contains the octets: 0xAA 0xAA 0x03 0x00 0x00
  0x00 0x88 0x0C. (0x880C is the assigned Ethertype for GSMP.)

  The maximum transmission unit (MTU) of the GSMP Message field is
  1492 octets.

  The virtual channel over which a GSMP session is established
  between a controller and the switch it is controlling is called
  the GSMP control channel. The default VPI and VCI of the GSMP
  control channel for LLC/SNAP encapsulated GSMP messages on an ATM
  data link layer is:

     VPI = 0
     VCI = 15.


3. Ethernet Encapsulation

  GSMP packets may be encapsulated on an Ethernet data link as
  illustrated:























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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Destination Address                      |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                         Source Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Ethertype (0x88-0C)       |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                                               |
   ~                         GSMP Message                          ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sender Instance                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Receiver Instance                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Pad                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Frame Check Sequence                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Destination Address
             For the SYN message of the adjacency protocol the
             Destination Address is the broadcast address
             0xFFFFFFFFFFFF. (Alternatively, it is also valid to
             configure the node with the unicast 48-bit IEEE MAC
             address of the destination. In this case the configured
             unicast Destination Address is used in the SYN message.)
             For all other messages the Destination Address is the
             unicast 48- bit IEEE MAC address of the destination.
             This address may be discovered from the Source Address
             field of messages received during synchronisation of the
             adjacency protocol.

  Source Address
             For all messages the Source Address is the 48-bit IEEE
             MAC address of the sender.

  Ethertype  The assigned Ethertype for GSMP is 0x880C.
  GSMP Message
             The maximum transmission unit (MTU) of the GSMP Message
             field is 1492 octets.



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  Sender Instance
             The Sender Instance number for the link obtained from
             the adjacency protocol. This field is already present in
             the adjacency protocol message. It is appended to all
             non- adjacency GSMP messages in the Ethernet
             encapsulation to offer additional protection against the
             introduction of corrupt state.

  Receiver Instance
             The Receiver Instance number is what the sender believes
             is the current instance number for the link, allocated
             by the entity at the far end of the link. This field is
             already present in the adjacency protocol message. It is
             appended to all non-adjacency GSMP messages in the
             Ethernet encapsulation to offer additional protection
             against the introduction of corrupt state.

  Pad
             The minimum length of the data field of an Ethernet
             packet is 46 octets. If necessary, padding should be
             added such that it meets the minimum Ethernet frame
             size. This padding should be octets of zero and it is
             not considered to be part of the GSMP message.

  After the adjacency protocol has achieved synchronisation, for
  every GSMP message received with an Ethernet encapsulation, the
  receiver must check the Source Address from the Ethernet MAC
  header, the Sender Instance, and the Receiver Instance. The
  incoming GSMP message must be discarded if the Sender Instance and
  the Source Address do not match the values of Sender Instance and
  Sender Name stored by the "Update Peer Verifier" operation of the
  GSMP adjacency protocol. The incoming GSMP message must also be
  discarded if it arrives over any port other than the port over
  which the adjacency protocol has achieved synchronisation. In
  addition, the incoming message must also be discarded if the
  Receiver Instance field does not match the current value for the
  Sender Instance of the GSMP adjacency protocol.


4. TCP/IP Encapsulation

  GSMP messages may be transported over an IP network using the TCP
  encapsulation. TCP provides reliable transport, network flow
  control, and end-system flow control suitable for networks that
  may have high loss and variable or unpredictable delay. The GSMP
  encapsulation in TCP/IP also provides sender authentication using
  an MD5 digest.




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  For TCP encapsulations of GSMP messages, the controller runs the
  client code and the switch runs the server code. Upon
  initialisation, the server is listening on GSMP's (proposed) well
  known port number. The controller establishes a TCP connection
  with each switch it manages. Adjacency protocol messages, which
  are used to synchronise the controller and switch and maintain
  handshakes, are sent by the controller to the switch after the TCP
  connection is established. GSMP messages other than adjacency
  protocol messages may be sent only after the adjacency protocol
  has achieved synchronisation.

4.1 Message Formats

  GSMP messages are sent over a TCP connection. A GSMP message is
  processed only after it is entirely received. A four-byte TLV
  header field is prepended to the GSMP message to provide
  delineation of GSMP messages within the TCP stream.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Type (0x88-0C)         |           Length              |
   |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                         GSMP Message                          ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Type
             This 2-octet field indicates the type code of the
             following message. The type code for GSMP messages is
             0x00-0C (i.e. the same as GSMP's Ethertype).

  Length:  This 2-octet unsigned integer indicates the total length
             of the GSMP message only. It does not including the 4-
             byte TLV header.

4.2 Security consideration

  To ensure the authenticity and security of GSMP messages which are
  transported through an IP network standard security measures
  should be used. GSMP provides for a two-layer security mechanism.
  The first layer of security mechanism is applied to network layer
  using IP-Sec (RFC 2401) [5].






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5. Security Considerations

  The security of GSMP's TCP/IP control channel has been addressed
  in Section 4.2. Security over ATM and Ethernet must be provided at
  the link layer. [need some more detail on minimum ip sec
  requirements -- ed]


References

     [1]  T. Worster, "General Switch Management Protocol,"
          Internet-Draft draft-ietf-gsmp-03, Jan 2000.

     [2]  "B-ISDN ATM Layer Specification," International
          Telecommunication Union, ITU-T Recommendation I.361, Mar.
          1993.

     [3]  "B-ISDN ATM Adaptation Layer (AAL) Specification,"
          International Telecommunication Union, ITU-T
          Recommendation I.363, Mar. 1993.

     [4]  Reynolds, J., and J. Postel, "Assigned Numbers," STD 2,
          RFC 1700, October 1994.

     [5] IP
               Sec
                    [together with text above, ip sec refs -- ed]


Authors' Addresses

   Tom Worster
   Ennovate Networks
   60 Codman Hill Rd
   Boxboro MA 01719 USA
   Tel +1 978-263-2002
   fsb@thefsb.org















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