RFC 2335 (rfc2335) - Page 2 of 7
A Distributed NHRP Service Using SCSP
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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
