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RFC 2443 - A Distributed MARS Service Using SCSP


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Network Working Group                                         J. Luciani
Request for Comments: 2443                                  Bay Networks
Category: Experimental                                          A. Gallo
                                                                     IBM
                                                           November 1998

                 A Distributed MARS Service Using SCSP

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

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

1. Introduction

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
   document, are to be interpreted as described in [5].

   The MARS is an extended analog of the ATMARP Server introduced in
   [4]. It provides the necessary connection and addressing services
   required by layer 3 multicast services over ATM. There are three
   basic elements to the MARS model. First, the MARS Server which
   manages and distributes layer 3 group membership information to the
   LIS. Second, MARS Clients which register with and query a single MARS
   Server for layer 3 multicast information. Third, MCS Clients which
   register with a single MARS Server and provide layer 3 multicast
   forwarding services for a LIS.

   Both MARS Clients and MCS Clients explicitly register with the MARS
   Server before exchanging layer 3 multicast information. During the
   registration process MARS Clients are place on the Cluster Control VC

   (CCVC) and MCS Clients are placed on the Server Control VC (SCVC).
   Both the CCVC and SCVC are then used to propagate layer 3 multicast
   updates to the clients which make up a LIS. During the registration
   process MARS Clients are also assigned a unique Cluster Member ID
   (CMI) which is used to identify reflected packets in the presence of
   MCS Clients.

   In the Distributed MARS Model there MAY be multiple MARS Servers in a
   given LIS, and since any MARS Server within the LIS MUST be able to
   provide layer 3 multicast information about any multicast group
   within the LIS, there MUST be a method by which to synchronize
   multicast information across all MARS 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 MARS
   Server database synchronization problem within a LIS. When SCSP is
   used to synchronize the caches of MARS Servers in a LIS, the LIS
   defines the boundary of and 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 the MARS Server is the
   client/server protocol.

2. Overview

   All MARS Servers belonging to a LIS are said to belong to a Server
   Group (SG).  A 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 0x0003 to
   signify that SCSP is synchronizing MARS 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 MARS Servers,
   the client/server protocol specific specification was written at the
   same time as SCSP, and thus a PID=0x0003 was assigned in [2].

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

   When a SG is using SCSP for synchronization, a MARS Client or MCS
   Client will register with only one MARS Server although it is allowed
   to choose any MARS Server in the SG for this registration. At
   registration time the MARS Client or MCS Client will be added to that
   MARS Servers respective CCVC or SCVC. Also, MARS Clients will be
   issued a unique CMI for the entire LIS. This document assumes at a
   minimum each MARS Server in the SG will be configured with a unique
   range of CMIs to assign to clients registering with that MARS Server.
   Use of some external means for allocating CMIs to MARS Servers in a
   SG is possible but beyond the scope of this document.

   When a MARS Client or MCS Client successfully registers with a MARS
   Server in the SG that MARS Server will propagate the registration
   information to its peer MARS Servers. The same propagation will occur
   for any subsequent group membership information learned from the
   clients. The peer MARS Server will then update its group membership
   database and propagate the information out its own CCVC or SCVC if
   needed.

   In the case of a MARS Server failure all peer MARS Servers in the SG
   MUST flush the client/group membership information learned from the
   failed MARS Server. The clients belonging to the failed MARS Servers
   CCVC and SCVC will migrate to the next available MARS Server as
   specified in Section 5.3 of [1]. When a client detects a failure of
   its MARS, it steps to the next backup MARS Server and attempts to
   register with the server. If the registration is successful the
   client will re-join all of its previous group membership information.
   If the registration fails, the process repeats until a functional
   MARS Server is found.

   Determining the operational state of a MARS Servers in a SG requires
   that each MARS Server send out an "alive" or "heartbeat" message
   similar to the MARS Redirect message sent out on the CCVC or SCVC for
   MARS Clients. However, this message will only be sent to MARS Servers
   in the SG and is from here on defined as the MARS Server Redirect
   Entry.

   In order to detect that a MARS Server failure has occurred each
   server MUST update it's MARS Server Redirect Entry state at least
   every 2 minutes, it is RECOMMENDED that it is updated every 1 minute.
   Failure to receive two consecutive MARS Server Redirect Entry updates
   from a given MARS Server in the SG will cause all membership
   information learned from this server to be flushed. The MARS Server
   Redirect Entry state is also used to create the MARS_REDIRECT_MAP
   messages sent out on CCVC for each MARS Server in the SG. The
   ordering of each server learned will be based on the MARS Servers
   SCSP Sender ID. The ordering of the MARS_REDIRECT_MAP will first

   contain the list of MARS Servers learned via MARS Server Redirect
   Entry updates in ascending order based on the SCSP Sender ID,
   followed by any externally configured or learned backup MARS Servers.

   In the case of a MARS Client or MCS Client failure where the client
   is unexpectedly removed from the CCVC or SCVC the MARS Server MUST
   notify its peer SG members via a proxy deregister for that client.
   Upon receiving a proxy deregister request from a peer SG member all
   membership information for the deregistering client MUST be removed.
   Any Clients sending multicast data to the failed client should also
   receive an unexpected removal of this client which will intern cause
   the sending client to revalidate the multicast groups current
   membership as outlined in Section 5.1.5.1 of [1].

3.  Format of the CSA Record MARS 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.

   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          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SNAP                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SNAP      |   Unused      |    Version    |   State       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Flags              |       Cluster Member ID       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Src Addr Len  | Group Addr Len| ATM Addr T/L  |ATM SubAddr T/L|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Source Protocol Address             (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Source ATM Address                  (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Source ATM SubAddress               (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Minimum Multicast Group Address     (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Maximum Multicast Group Address     (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Hardware Type
     Defines the type of "link layer" addresses being carried.  This
     value is the ATM Forum 'address family number' specified in [3] as
     15 decimal (0x000F).  This is the mar$afn field defined in [1].

   Protocol Type
     This field is the protocol type number for the protocol using MARS
     from [3].  (IPv4 is 0x0800).  This is the mar$pro.type field from
     [1].

   Protocol SNAP
     This field is the optional protocol SNAP extension to protocol
     type. This is the mar$pro.snap field from [1].

   Version Number
     0                    MARS Specific part of the CSA record.
     0x01                 Reserved for NHRP.
     0x02 - 0xEF          Reserved for future use by the IETF.
     0xF0 - 0xFE          Allocated for use by the ATM Forum.
     0xFF                 Experimental/Local use.
     Version Number for this document MUST be set to 0x00.

   State
     1   MARS Server Redirect Entry.
     2   MCS Serve/Register request.
     3   MARS Client Join/Register request.
     4   MARS Client Leave/Deregister request.
     5   MCS Unserve/Deregister request.

     All other State values should cause the CSA to be discarded.

   Flags
     The flags field is used to contain several flags and is similar to
     the mar$flags field from [1].
       mar$flags
          Bit 15   - mar$flags.layer3grp
          Bit 13   - mar$flags.register
          Bit 0-7  - mar$flags.sequence

       All remaining bits are reserved and MUST be zero. The
       mars$flags.sequence field is of local significance only to the
       Local Server (LS).

   Cluster Member CMI
     This field contains the CMI which uniquely identifies each endpoint
     within a LIS. This is the mar$cmi field from [1].

   Src Addr Len
     This field contains the length of the Source Protocol Address
     field.  For IPv4, the value is 4 if an address is specified. A null
     (non-existent) address MUST be coded as zero length, and no space
     allocated for it in the message body.  This is the mar$spln field
     from [1].

   Group Addr Len
     This field contains the length of the Group Protocol Address field.
     For IPv4, the value is 4 if an address is specified. A null (non-
     existent) address MUST be coded as zero length, and no space
     allocated for it in the message body.  This is the mar$tpln field
     from [1].

   ATM Addr T/L
     This field contains the type and length of the Source ATM Address
     field.  The type and length encoding is described in Section 5.1.2
     of [1].

   ATM SubAddr T/L
     This field contains the type and length of the Source ATM
     SubAddress field.  The type and length encoding is described in
     Section 5.1.2 of [1].

   Source Protocol Address
     This is the internetwork address for the source of an address
     binding in a MARS server cache entry. If null, no storage will be
     allocated.  This is the mar$spa field from [1].

   Source ATM Address
     This is the Source's ATM address of an address binding in a MARS
     server cache entry.  The address, if specified, is E.164 or ATM
     Forum NSAPA. This is the mar$sha field from [1].

   Source ATM SubAddress
     This is the Source's ATM subaddress of an address binding in a MARS
     server cache entry.  The subaddress, if specified, is an ATM Forum
     NSAPA.  If null, no storage will be allocated. This is the mar$ssa
     field from [1].

   Minimum Multicast Group Address
     This is the internetwork address of the lower bound on the range of
     multicast group addresses for the address binding in a MARS server
     cache entry. If null, no storage will be allocated. This is the
     mar$min.N field from [1].

   Maximum Multicast Group Address
     This is the internetwork address of the upper bound on the range of
     multicast group addresses for the address binding in a MARS server
     cache entry. If null, no storage will be allocated. This is the
     mar$max.N field from [1].

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 = 0x0003
   Sender ID Len = 0x04
   Recvr ID Len = 0x04

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

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
   fields.

5.  Detailed State Descriptions

5.1  MARS Server Redirect Entry.

   The MARS Server Redirect Entry is used to determine the operational
   state of a MARS Server in the SG. Each server MUST update it's MARS
   Server Redirect Entry state at least every 2 minutes, it is
   RECOMMENDED that it is updated every 1 minute.

   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          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SNAP                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SNAP      |   Unused      |    Version    |   State       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Flags              |       Cluster Member ID       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Src Addr Len  | Group Addr Len| ATM Addr T/L  |ATM SubAddr T/L|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Source ATM Address                  (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Source ATM SubAddress               (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Hardware Type
     This value is the ATM Forum 'address family number' specified in
     [3] as 15 decimal (0x000F).

   Protocol Type
     This field is the protocol type number for the protocol using MARS
     from [3].  (IPv4 is 0x0800).

   Protocol SNAP
     This field is the optional protocol SNAP extension to protocol
     type.  This is the mar$pro.snap field from [1].

   Version Number
     Version Number for this document MUST be set to 0x00.

   State
     State value is coded as 1 decimal for a MARS Server Redirect Entry.

   The Flags, Cluster Member ID, Src Addr Len, and Group Addr Len fields
   are unused and set to zero.

   The ATM Addr T/L, ATM SubAddr T/L, Source ATM Address, and Source ATM
   SubAddress fields define the ATM address for the source of the MARS
   Server Redirect Entry in the SG. The coding for these fields are the
   same as described in Section 3 of this document.

   Failure to receive two consecutive MARS Server Redirect Entry updates
   from a given MARS Server in the SG will cause all membership
   information learned from this server to be flushed. When a valid MARS
   Server Redirect Entry update is received the source of this update
   will be placed into the table of backup MARS Servers sent in the
   MARS_REDIRECT_MAP message. The ordering of servers in the
   MARS_REDIRECT_MAP will first contain the list of MARS Servers learned
   via MARS Server Redirect Entry updates in ascending order based on
   the SCSP Sender ID, followed by any externally configured or learned
   backup MARS Servers. The format of the MARS_REDIRECT_MAP can be found
   in Section 5.4.3 of [1].

5.2  MCS Serve/Register request.

   The MCS Serve/Register request is used to propagate the registering
   or servicing of specific groups by an MCS Client within the SG
   domain. It is similar to an MARS_MSERV request defined in Section
   6.2.2 and 6.2.3 of [1]. When a MARS Server in the SG successfully
   adds a new MCS Client to it's SCVC or adds MCS support for a specific
   group it MUST send a MCS Serve/Register request to the SG. An MCS
   Client can only register with one MARS Server in the SG.

   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          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SNAP                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SNAP      |   Unused      |    Version    |   State       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Flags              |       Cluster Member ID       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Src Addr Len  | Group Addr Len| ATM Addr T/L  |ATM SubAddr T/L|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Source Protocol Address             (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Source ATM Address                  (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Source ATM SubAddress               (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Minimum Multicast Group Address     (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Maximum Multicast Group Address     (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Hardware Type
     This value is the ATM Forum 'address family number' specified in
     [3] as 15 decimal (0x000F).

   Protocol Type
     This field is the protocol type number for the protocol using MARS
     from [3].  (IPv4 is 0x0800).

   Protocol SNAP
     This field is the optional protocol SNAP extension to protocol
     type.  This is the mar$pro.snap field from [1].

   Version Number
     Version Number for this document MUST be set to 0x00.

   State
     State value is coded as 2 decimal for a MCS Serve/Register request.

   Flags
     The flags field is used to contain several flags:

       mar$flags
          Bit 15   - mar$flags.layer3grp
          Bit 13   - mar$flags.register
          Bit 0-7  - mar$flags.sequence

     The mar$flags.register bit MUST be set the same as in the
     originating MARS_MSERV request. The mar$flags.layer3grp bit MUST be
     zero and the mar$flags.sequence bits are of local significance only
     to the LS.

   Cluster Member CMI
     This field contains the CMI assigned by the MARS Server which
     processed the MARS_MSERV request and uniquely identifies the MCS
     Client in the MARS server cache.

   Src Addr Len
     This field contains the length of the Source Protocol Address
     field.  For IPv4, the value is 4 if an address is specified. A null
     (non-existent) address MUST be coded as zero length, and no space
     allocated for it in the message body.

   Group Addr Len
     This field contains the length of the Group Protocol Address field.
     If the register bit in the flags field is set to 1 in the request
     this field MUST be zero.  If the register bit is zero in the flags
     field the value of this field for IPv4 is 4.

   ATM Addr T/L
     This field contains the type and length of the Source ATM Address
     field for the MCS Client that originated the MARS_MSERV request.
     The type and length encoding is described in Section 3.

   ATM SubAddr T/L
     This field contains the type and length of the Source ATM
     SubAddress field for the MCS Client that originated the MARS_MSERV
     request.  The type and length encoding is described in Section 3.

   Source Protocol Address
     This is the internetwork address for the source of an address
     binding in a MARS server cache entry. If Src Addr Len is set to
     zero no storage will be allocated.

   Source ATM Address
     This is the MCS Client's ATM address of an address binding in a
     MARS server cache entry. The address is E.164 or ATM Forum NSAPA.

   Source ATM SubAddress
     This is the MCS Client's ATM subaddress of an address binding in a
     MARS server cache entry. The subaddress, if specified, is an ATM
     Forum NSAPA.  If null, no storage will be allocated.

   Minimum Multicast Group Address
     This is the internetwork address of the lower bound on the range of
     multicast group addresses for the address binding in a MARS server
     cache entry. If Group Addr Len is set to zero no storage will be
     allocated.

   Maximum Multicast Group Address
     This is the internetwork address of the upper bound on the range of
     multicast group addresses for the address binding in a MARS server
     cache entry. If Group Addr Len is set to zero no storage will be
     allocated.

   An MCS Client can only register with one MARS Server in the SG and is
   only placed on the SCVC for the MARS Server for which it is
   registered with.

   When a MCS Client Serve/Register request specifying a group address
   is received by a MARS Server it MUST create a cache entry associated
   with this client. In addition to adding the cache entry it MUST send
   out a MARS_MIGRATE message on it's CCVC. This is needed so that
   clients using a mesh topology can migrate to a server based topology.
   Details regarding the MARS_MIGRATE message can be found in Section
   5.1.6 of [1].

5.3  MARS Client Join/Register request.

   The MARS Client Join/Register request is used to propagate the
   registering or joining of specific group ranges by MARS Clients
   within the SG domain.  It is similar to the MARS_JOIN request defined
   in Sections 5.2.1 to 5.2.3 of [1]. When a MARS Server in the SG
   successfully registers a new MARS Client or a registered client joins
   a specific group address range the MARS Server MUST send a MARS
   Client Join/Register request to the SG. A MARS Client can only
   register with one MARS Server in the SG and is placed only on that
   servers CCVC.

   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          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SNAP                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SNAP      |   Unused      |    Version    |   State       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Flags              |       Cluster Member ID       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Src Addr Len  | Group Addr Len| ATM Addr T/L  |ATM SubAddr T/L|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Source Protocol Address             (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Source ATM Address                  (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Source ATM SubAddress               (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Minimum Multicast Group Address     (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Maximum Multicast Group Address     (variable length)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Hardware Type
     This value is the ATM Forum 'address family number' specified in
     [3] as 15 decimal (0x000F).

   Protocol Type
     This field is the protocol type number for the protocol using MARS
     from [3].  (IPv4 is 0x0800).

   Protocol SNAP
     This field is the optional protocol SNAP extension to protocol
     type.  This is the mar$pro.snap field from [1].

   Version Number
     Version Number for this document MUST be set to 0x00.

   State
     State value is coded as 3 decimal for a MARS Client Join/Register
     request.

   Flags
     The flags field is used to contain several flags:

       mar$flags
          Bit 15   - mar$flags.layer3grp
          Bit 13   - mar$flags.register
          Bit 0-7  - mar$flags.sequence

     The mars$flags.layer3grp and mar$flags.register bits MUST be set
     the same as in the originating MARS_JOIN request. The
     mar$flags.sequence bits are of local significance only to the LS.

   Cluster Member CMI
     This field contains the CMI assigned by the MARS Server which
     processed the MARS_JOIN request and uniquely identifies the MARS
     Client in the MARS server cache.

   Src Addr Len
     This field contains the length of the Source Protocol Address
     field.  For IPv4, the value is 4 if an address is specified. A null
     (non-existent) address MUST be coded as zero length, and no space
     allocated for it in the message body.

   Group Addr Len
     This field contains the length of the Group Protocol Address field.
     If the register bit in the flags field is set to 1 in the request
     this field MUST be zero.  If the register bit is zero in the flags
     field the value of this field for IPv4 is 4.

   ATM Addr T/L
     This field contains the type and length of the Source ATM Address
     field for the MARS Client that originated the MARS_JOIN request.
     The type and length encoding is described in Section 3.

   ATM SubAddr T/L
     This field contains the type and length of the Source ATM
     SubAddress field for the MARS Client that originated the MARS_JOIN
     request.  The type and length encoding is described in Section 3.

   Source Protocol Address
     This is the internetwork address for the source of an address
     binding in a MARS server cache entry. If Src Addr Len is set to
     zero no storage will be allocated.

   Source ATM Address
     This is the MARS Client's ATM address of an address binding in a
     MARS server cache entry. The address is E.164 or ATM Forum NSAPA.

   Source ATM SubAddress
     This is the MARS Client's ATM subaddress of an address binding in a
     MARS server cache entry. The subaddress, if specified, is an ATM
     Forum NSAPA.  If null, no storage will be allocated.

   Minimum Multicast Group Address
     This is the internetwork address of the lower bound on the range of
     multicast group addresses for the address binding in a MARS server
     cache entry. If Group Addr Len is set to zero no storage will be
     allocated.

   Maximum Multicast Group Address
     This is the internetwork address of the upper bound on the range of
     multicast group addresses for the address binding in a MARS server
     cache entry. If Group Addr Len is set to zero no storage will be
     allocated.

   An MARS Client can only register with one MARS Server in the SG and
   is only placed on the CCVC for the MARS Server for which it is
   registered with. If the mar$flags.layer3grp is set to 1 than the
   Minimum and Maximum Multicast Group Addresses MUST be equal for IPv4.

   When a MARS Client Join/Register request is sent with the
   mar$flags.register bit set to 1 all of the servers in the SG will
   create a cache entry for this client using the information in the
   request.

   When a registered MARS Client issues a MARS_JOIN for a specific group
   address range a MARS Client Join/Register request MUST be sent to the
   servers in the SG. The actions taken by each server in the SG depend
   on previous group membership actions and MCS supported groups.

   Each MARS Server MUST perform the necessary redistribution and hole
   punching algorithms before propagating this request to the CCVC and
   SCVC on each server. The redistribution and hole punching algorithms
   used for propagating join requests to the CCVC are the same as
   defined in Sections 6.1.2 and 6.2.4 of [1]. If the originating
   MARS_JOIN request is a duplicate of a previously joined range or
   contains no group address range than a MARS Client Join/Register MUST
   NOT be sent to the SG.

   The redistribution and hole punching algorithms used for propagating
   join requests as MARS_SJOIN request on a SCVC is the same as Section
   6.2.4 except for the following. Only the MARS Servers which contain
   the registered MCS Clients for the target group ranges should
   propagate this information to their SCVCs.

5.4  MARS Client Leave/Deregister request.

   The MARS Client Leave/Deregister request is used to propagate the
   deregistering or leaving of specific group ranges by registered MARS
   Clients within the SG domain. It is similar to the MARS_LEAVE request
   defined in Sections 5.2.1 to 5.2.3 of [1]. When a MARS Server in the
   SG successfully deregisters a registered MARS Client or a registered
   client leaves a specific group address range for which it had joined
   the MARS Server MUST send a MARS Client Leave/Deregister request to
   the SG. If a registered MARS Client is unexpectedly removed from the
   CCVC the MARS Server MUST act as a proxy and send a MARS Client
   Leave/Deregister request to the SG.

   The format and meanings of the fields in a MARS Client
   Leave/Deregister request are the same as in Section 5.3 except the
   State is coded as 4 decimal for a MARS Client Leave/Deregister
   request.

   When a MARS Client Leave/Deregister request is sent with the
   mar$flags.register bit set to 1 all of the servers in the SG
   receiving this update MUST purge all cache entries for this client.

   When a registered MARS Client issues a MARS_LEAVE for a specific
   group address range a MARS Client LEAVE/Deregister request MUST be
   sent to the servers in the SG. The actions taken by each server in
   the SG depend on previous group membership actions and MCS supported
   groups.

   Each MARS Server MUST perform the necessary redistribution and hole
   punching algorithms before propagating this request to the CCVC and
   SCVC on each server. The redistribution and hole punching algorithms
   used for propagating leave requests to the CCVC are the same as
   defined in Sections 6.1.2 and 6.2.4 of [1]. If the originating
   MARS_LEAVE request does not correspond to a previously joined range
   or contains no group address range than a MARS Client
   Leave/Deregister MUST NOT be sent to the SG.

   The redistribution and hole punching algorithms used for propagating
   leave requests as MARS_SLEAVE requests on a SCVC is the same as
   Section 6.2.4 except for the following. Only the MARS Servers which
   contain the registered MCS Clients for the target group ranges should
   propagate this information to their SCVCs.

5.5  MCS Unserve/Deregister request.

   The MCS Unserve/Deregister request is used to propagate the
   deregistering or unservicing of specific groups by a registered MCS
   Client within the SG domain. It is similar to an MARS_MUNSERV request

   defined in Section 6.2.2 and 6.2.3 of [1]. When a MARS Server in the
   SG successfully deregisters a registered MCS Client or registered MCS
   Client stops serving a specific group address range for which it had
   serviced the MARS Server MUST send a MCS Unserve/Deregister request
   to the SG. If a registered MCS Client is unexpectedly removed from
   the SCVC the MARS Server owning the SCVC MUST act as a proxy and send
   a MCS Unserve/Deregister request to the SG.

   The format and meanings of the fields in a MCS Unserve/Deregister
   request are the same as in Section 5.2 except the State is coded as 5
   decimal for a MCS Unserve/Deregister request.

   When a MCS Client Unserve/Deregister request is sent with the
   mar$flags.register bit set to 1 all of the servers in the SG
   receiving this update MUST purge all cache entries for this client.

   When a registered MCS Client issues a MARS_MUNSERV for a specific
   group address range being served a MCS Client Unserve/Deregister
   request MUST be sent to the servers in the SG. The members of the SG
   that receive this update must then clear the cache entry associated
   with this MCS Client.

   In addition to clearing one or more cache entries associated with
   receiving a  MCS Client Unserve/Deregister request each MARS Server
   in the SG MUST send out a MARS_LEAVE message on it's CCVC in order
   for clients to change back to a mesh topology.

6.  Security Considerations

   There is no mechanism to encrypt the CSA Record MARS Specific Part of
   the message exchanged between servers. However, there are base SCSP
   security features in the SCSP Protocol Independent part [2] which can
   be used to protect against attacks.

   Any SCSP MARS is susceptible to Denial of Service (DOS) attacks. A
   rouge MARS Client can inundate its Server with MARS packets. This is
   a base MARS problem as currently defined by [1]. A rouge host can
   also inundate its neighboring SCSP MARS with SCSP packets. However,
   if the authentication option is used, the SCSP MARS databases will
   not become corrupted, as the bogus packets will be discarded when the
   authentication check fails.

   Due to the pair wise authentication model of SCSP MARS, the
   information received from any properly authenticated server is
   trusted and propagated throughout the server group. Consequently, if
   security of any SCSP MARS server is compromised, the entire database
   becomes vulnerable to corruption originating from the compromised
   server.

References

   [1] Armitage, G., "Support for Multicast over UNI 3.0/3.1 based ATM
       Networks", RFC 2022, November 1996.

   [2] Luciani, J., Armitage, G., Halpern, J. and N. Doraswamy, "Server
       Cache Synchronization Protocol", RFC 2334, April 1998.

   [3] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1700,
       October 1994.  See also: http://www.iana.org/numbers.html

   [4] Laubach, M., "Classic IP and ARP over ATM", RFC 1577, January
       1994.

   [5] Bradner, S., "Key Words for use in RFCs to Indicate Requirement
       Levels," BCP 14, RFC 2119, March 1997.

Acknowledgments

   The authors would like to thank Grenville Armitage for his previous
   distributed MARS work and also the members of the ION working group
   of the IETF, whose review and discussion of this document has been
   invaluable.

Authors' Addresses

   James V. Luciani
   Bay Networks, Inc.
   3 Federal Street, BL3-04
   Billerica, MA  01821

   Phone: +1-508-916-4734
   EMail: luciani@baynetworks.com

   Anthony M. Gallo
   IBM, Networking Hardware Division
   Dept. M6LA/B664
   P.O. Box 12195
   Research Triangle Park, NC 27709

   Phone: +1-919-254-9889
   EMail: gallo@raleigh.ibm.com

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