RFC 2335 (rfc2335) - Page 2 of 7
A Distributed NHRP Service Using SCSP
Alternative Format: Original Text Document
RFC 2335 NHRP Using SCSP April 1998
SCSP is defined in two parts: the protocol independent part and the
client/server protocol specific part. The protocol independent part
is defined in [2] whereas this document will specify the
client/server protocol specific part where NHRP is the client/server
protocol.
This document is separate from [2] because it was felt that it was
desirable to allow the client/server protocol specific part
specification for NHRP to progress independently from the protocol
independent specification.
2. Overview
All NHSs 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 0x0002 to signify that SCSP synchronizing
NHS 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 as described in Section C of
[2]. In the case of NHRP, the client/server protocol specific
specification was initially written at the same time as SCSP, and
thus a PID=0x0002 was assigned by the author.
SCSP places no topological requirements upon an NHRP SG. Obviously,
however, the resultant graph of NHSs must span the set of NHSs to be
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, an NHC will register
with only one NHS, but the NHC MAY use any NHS in the SG. When an
NHC wishes to leave a SG, the NHC MUST do one of the following: 1)
the NHC MUST send an NHRP Purge Request for itself requesting a
reply, and it MUST wait for an NHRP Purge Reply, 2) the NHC MUST keep
the Request ID it used when registering itself in non-volatile RAM
and use a Request ID larger than the one saved when re-registering,
or 3) the NHC MUST not re-register for a time equal to the Holding
Time specified in the previous registration. It is necessary to do
one of the previous in order to prevent the unlikely case of race
conditions from occurring during updated. In the case where method 2
is used, the NHS with which the NHC registered uses its ID as the OID
and the Request ID from the NHC as the CSA Sequence Number in the
CSA(S) Record.
Luciani Standards Track