RFC 2332 (rfc2332) - Page 2 of 52
NBMA Next Hop Resolution Protocol (NHRP)
Alternative Format: Original Text Document
RFC 2332 NBMA NHRP April 1998
Operation of NHRP as a means of establishing a transit path across an
NBMA subnetwork between two routers will be addressed in a separate
document (see [13]).
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 [15].
The NBMA Next Hop Resolution Protocol (NHRP) allows a source station
(a host or router), wishing to communicate over a Non-Broadcast,
Multi-Access (NBMA) subnetwork, to determine the internetworking
layer addresses and NBMA addresses of suitable "NBMA next hops"
toward a destination station. A subnetwork can be non-broadcast
either because it technically doesn't support broadcasting (e.g., an
X.25 subnetwork) or because broadcasting is not feasible for one
reason or another (e.g., an SMDS multicast group or an extended
Ethernet would be too large). If the destination is connected to the
NBMA subnetwork, then the NBMA next hop is the destination station
itself. Otherwise, the NBMA next hop is the egress router from the
NBMA subnetwork that is "nearest" to the destination station.
One way to model an NBMA network is by using the notion of logically
independent IP subnets (LISs). LISs, as defined in [3] and [4], have
the following properties:
1) All members of a LIS have the same IP network/subnet number
and address mask.
2) All members of a LIS are directly connected to the same
NBMA subnetwork.
3) All hosts and routers outside of the LIS are accessed via
a router.
4) All members of a LIS access each other directly (without
routers).
Address resolution as described in [3] and [4] only resolves the next
hop address if the destination station is a member of the same LIS as
the source station; otherwise, the source station must forward
packets to a router that is a member of multiple LIS's. In multi-LIS
Luciani, et. al. Standards Track