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Versions: 00 01                                                         
Internetworking Over NBMA                               James V. Luciani
INTERNET-DRAFT                                            (Bay Networks)
<draft-ietf-ion-scsp-atmarp-01.txt>                         Joel Halpern
                                               (Newbridge Networks, Inc)
                                                          Barbara A. Fox
                                                   (Lucent Technologies)
                                                        Expires May 1999

                A Distributed ATMARP Service Using SCSP

Status of this Memo

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).


   This document describes a method for distributing an ATMARP service
   within a LIS[1].  This method uses the Server Cache Synchronization
   Protocol (SCSP)[2] to synchronize the ATMARP server databases within
   a LIS.  When SCSP is used to synchronize the caches of ATMARP servers
   in a LIS, the LIS defines the boundary of an SCSP Server Group (SG).

1. Introduction

   An ATMARP Client implicitly registers (e.g., by sending an ATMARP
   Request for itself; see [1]) and refreshes its own ATMARP information
   with a single ATMARP server in its atm$arp-req-list table.  In
   addition, the ATMARP Client uses the ATMARP service to gain access to
   and re-validate ATMARP information about other ATMARP Clients in its

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   Logical IP Subnet (LIS). Since, there MAY be multiple ATMARP servers
   in a given LIS, and since any ATMARP server within the LIS MUST be
   able to reply to ATMARP requests for ATMARP information about any
   ATMARP Clients within the LIS, there MUST be a method by which to
   synchronize ATMARP information across all ATMARP Servers within the
   LIS.  The Server Cache Synchronization Protocol (SCSP) solves the
   generalized server synchronization/cache-replication problem for
   distributed databases, and thus SCSP MAY be applied to the ATMARP
   server database synchronization problem with the LIS.  When SCSP is
   used to synchronize the caches of ATMARP servers in a LIS, the LIS
   defines the boundary of an SCSP Server Group (SG).

   SCSP is defined in two parts: the protocol independent part and the
   client/server protocol specific part.  The protocol independent part
   is specified in [2] whereas this document will specify the
   client/server protocol specific part where ATMARP is the
   client/server protocol.

2. Overview

   All ATMARP servers belonging to a Logical IP Subnet (LIS)[1] are said
   to belong to a Server Group (SG).  An SG is identified by, not
   surprisingly, its SGID which is contained in a field in all SCSP
   packets.  All SCSP packets contain a Protocol ID (PID) field as well.
   This PID field is set to 0x0001 to signify that SCSP is synchronizing
   ATMARP server databases as opposed to synchronizing some other
   protocol's databases (see Section B.2.0.1 of [2] for more details).
   In general, PIDs for SCSP will be assigned by IANA upon request given
   that a client/server protocol specific specification has been
   written. In the case of ATMARP, the client/server protocol specific
   specification was initially written at the same time as SCSP, and
   thus a PID=0x0001 was assigned by the author.

   SCSP places no topological requirements upon an ATMARP SG.
   Obviously, however, the resultant graph of ATMARP servers must span
   the set of ATMARP servers to be synchronized.  For more information
   about the client/server protocol independent part of SCSP, the reader
   is encouraged to see [2].

   When an ATMARP SG is using SCSP for synchronization, a given ATMARP
   Client will use only one ATMARP server and it will use that server
   for remainder of its participation in the SG.  This server is said to
   be the "serving ATMARP server."  There needs to be some hysteresis on
   refreshes since every ATMARP Request may cause a cache update/refresh
   in the serving ATMARP Server, and such refreshes might cause
   excessive traffic if propagated to all ATMARP Servers in the SG.  In
   the case of mere refreshes, where no change occurs to the ATMARP

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   Server's cache entry for the ATMARP Client, SCSP updates will occur
   at a maximum rate of once every 10+Random(2) minutes.

   When an ATMARP server receives database information via SCSP, it
   checks it against the locally registered clients.  Information not
   related to locally registered clients is simply accepted.  (Note to
   implementors: this may result in transient multiple possible
   resolutions for an IP->ATM address binding.  The server may provide
   any one of these bindings to a client who sends in an ATMARP
   request.)  If there is a collision with the locally registered client
   base, then the base must be checked for whether the information is
   associated with a connected client.  If it is not, then the local
   information is presumed to be supersceded and must be purged and
   transmitted to peer ATMARP servers with 0 lifetime.

   If the local information is associated with a connected client, then
   an effort needs to be made to determine if the remote information is
   also associated with a connected client.  Therefore:

   1) The ATMARP server will wait an interval T1 before taking any action.
      If the duplicative information is purged, no further action is
   2) If the duplicate information is not purged, the ATMARP Server will
      then consider both sets of information (local and remote) to be
      invalid.  A Network Management notification is generated.
   3) The ATMARP Server will disconnect the local client.  An ARPNAK should
      be sent to the client prior to disconnecting the VC.  After waiting
      an interval T2, the ATMARP Server will purge the locally generated
      information from the system.  (This avoids the potential for one of
      the two clients to randomly remain in the system when both are wrong.)

   When an ATMARP server receives a registration from a client, it
   checks the database of known clients.  If there is a known local
   collision, the procedures from Classic II are followed.  If there is
   a collision with an entry in the remote database, then the
   registration is accepted and flooded out, and the timer from (1)
   above is started so as to resolve the apparent collision.

3.  Format of the CSA Record ATMARP Specific Part

   CSA Records in SCSP contain a "Client/Server Protocol Specific Part"
   which contains the non-protocol independent information for a given
   server's cache entry.

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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
   |        Hardware Type          |        Protocol Type          |
   |   Lifetime    |  ATM Addr T/L |ATM SubAddr T/L| Proto Addr Len|
   |                ATM Address      (variable length)             |
   |              ATM SubAddress     (variable length)             |
   |                 Protocol Address  (variable length)           |

   With the exception of the State and unused fields, these fields
   contain the values specified in the ATMARP Request and Reply packets
   defined in [1] which are used to create, update, and access ATMARP
   server cache entries.

   Hardware Type
     Defines the type of "link layer" addresses being carried.  This
     value is the ATM Forum 'address family number' specified in [3] as
     19 decimal (0x0013).  This is the ar$hrd field defined in [1].

   Protocol Type
     This field is the protocol type number for the protocol using
     ATMARP from [3].  (IP is 0x0800).  This is the ar$pro field from

     This field contains a value (in minutes) which represents the
     lifetime of the ATMARP entry.  A value of 0 indicates that the
     entry should be deleted.

     Note that a time-out of a cache entry does not cause a CSA Record
     to be sent because, if everything is working properly then all
     ATMARP servers have the cache entry timing out at the same time.
     Thus, the individual servers would take the appropriate actions

   ATM Addr T/L
     This field contains the type and length of the ATM Address field.
     The type and length encodings are described in Section 8.7.3 of

   ATM SubAddr T/L
     This field contains the type and length of the ATM SubAddress
     field.  The type and length encodings are described in Section

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     8.7.3 of [1].

   Proto Addr Len
     This field contains the length of the Protocol Address field.  For
     IPv4, the value is 4.

   ATM Address
     This is the ATM address of an address binding in an ATMARP server
     cache entry.  The address, if specified, is E.164 or ATM Forum

   ATM Subaddress
     This is the ATM subaddress of an address binding in an ATMARP
     server cache entry.  The subaddress, if specified, is an ATM Forum
     NSAPA.  If null, no storage will be allocated.

   Protocol Address
     This is the internetwork address of an address binding in an ATMARP
     server cache entry.

4.  Values for SCSP Protocol Independent Part

   The following sections give values for fields of the SCSP Protocol
   Independent Part of the various SCSP messages.

4.1 Values for the SCSP "Mandatory Common Part"

   Protocol ID = 0x0001
   Sender ID Len = 0x04
   Recvr ID Len = 0x04

   See Section B.2.0.1 of [2] for a detailed description of these

4.2 Values for the SCSP "CSAS Record"

   Cache Key Len = 0x04
   Orig ID Len = 0x04

   See Section B.2.0.2 of [2] for a detailed description of these


[1] "Classical IP and ARP over ATM", Mark Laubach and Joel Halpern,
    RFC 2225.

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[2] "Server Cache Synchronization Protocol (SCSP)", Luciani,
    Armitage, Halpern, RFC 2334.

[3] Assigned Numbers, J. Reynolds and J. Postel, RFC 1700.

   We would like to thank the members of the ION working group of the
   IETF, whose review and discussion of this document has been

Author's Address

   James V. Luciani
   Bay Networks, Inc.
   3 Federal Street, BL3-04
   Billerica, MA  01821
   phone: +1-508-916-4734
   email: luciani@baynetworks.com

   Joel Halpern
   Newbridge Networks, Inc
   593 Herndon Parkway
   Herndon, VA  22070-5241
   phone: +1-703-736-5954
   email: jhalpern@Newbridge.com

   Barbara A. Fox
   Lucent Technologies
   300 Baker Ave, Suite 100
   Concord, MA  01742-2168
   phone: +1-978-287-2843
   email: barbarafox@lucent.com

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