RFC2443 - 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", RFC2022, November 1996.

[2] Luciani, J., Armitage, G., Halpern, J. and N. Doraswamy, "Server
Cache Synchronization Protocol", RFC2334, April 1998.

[3] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC1700,
October 1994. See also: http://www.iana.org/numbers.html

[4] Laubach, M., "Classic IP and ARP over ATM", RFC1577, January
1994.

[5] Bradner, S., "Key Words for use in RFCs to Indicate Requirement
Levels," BCP 14, RFC2119, 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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