Network Working Group J. Luciani
Request for Comments: 2334 Bay Networks
Category: Standards Track G. Armitage
Bellcore
J. Halpern
Newbridge
N. Doraswamy
Bay Networks
April 1998
Server Cache Synchronization Protocol (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 the Server Cache Synchronization Protocol
(SCSP) and is written in terms of SCSP's use within Non Broadcast
Multiple Access (NBMA) networks; although, a somewhat straight
forward usage is applicable to BMA networks. SCSP attempts to solve
the generalized cache synchronization/cache-replication problem for
distributed protocol entities. However, in this document, SCSP is
couched in terms of the client/server paradigm in which distributed
server entities, which are bound to a Server Group (SG) through some
means, wish to synchronize the contents (or a portion thereof) of
their caches which contain information about the state of clients
being served.
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 [10].
It is perhaps an obvious goal for any protocol to not limit itself to
a single point of failure such as having a single server in a
client/server paradigm. Even when there are redundant servers, there
Luciani, et. al. Standards Track [Page 1]
RFC 2334 SCSP April 1998
still remains the problem of cache synchronization; i.e., when one
server becomes aware of a change in state of cache information then
that server must propagate the knowledge of the change in state to
all servers which are actively mirroring that state information.
Further, this must be done in a timely fashion without putting undue
resource strains on the servers. Assuming that the state information
kept in the server cache is the state of clients of the server, then
in order to minimize the burden placed upon the client it is also
highly desirable that clients need not have complete knowledge of all
servers which they may use. However, any mechanism for
synchronization should not preclude a client from having access to
several (or all) servers. Of course, any solution must be reasonably
scalable, capable of using some auto-configuration service, and lend
itself to a wide range of authentication methodologies.
This document describes the Server Cache Synchronization Protocol
(SCSP). SCSP solves the generalized server synchronization/cache-
replication problem while addressing the issues described above.
SCSP synchronizes caches (or a portion of the caches) of a set of
server entities of a particular protocol which are bound to a Server
Group (SG) through some means (e.g., all NHRP servers belonging to a
Logical IP Subnet (LIS)[1]). The client/server protocol which a
particular server uses is identified by a Protocol ID (PID). SGs are
identified by an ID which, not surprisingly, is called a SGID. Note,
therefore, that the combination PID/SGID identifies both the
client/server protocol for which the servers of the SG are being
synchronized as well as the instance of that protocol. This implies
that multiple instances of the same protocol may be in operation at
the same time and have their servers synchronized independently of
each other. An example of types of information that must be
synchronized can be seen in NHRP[2] using IP where the information
includes the registered clients' IP to NBMA mappings in the SG LIS.
The simplest way to understand SCSP is to understand that the
algorithm used here is quite similar to that used in OSPF[3]. In
fact, if the reader wishes to understand more details of the
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