RFC 2333 (rfc2333) - Page 2 of 9

NHRP Protocol Applicability Statement

RFC 2333              NHRP Protocol Applicability             April 1998


   with an inter-LIS address resolution mechanism at the end of which
   both stations can exchange packets without having to use the services
   of intermediate routers.  This feature is also referred to as
   "short-cut" routing.  If the destination station is not part of the
   logical NBMA network, NHRP provides the source with the NBMA address
   of the current egress router towards the destination.

   The second generalization is that NHRP is not specific to a
   particular NBMA technology.  Of course, [3] assumes an ATM network
   and [4] assumes an SMDS network at their respective subnetwork
   layers.

   NHRP is specified for resolving the destination NBMA addresses of IP
   datagrams over IP subnets within a large NBMA cloud.  NHRP has been
   designed to be extensible to network layer protocols other than IP,
   possibly subject to other network layer protocol specific additions.

   As an important application of NHRP, the Multiprotocol Over ATM
   (MPOA) Working Group of the ATM Forum has decided to adopt and to
   integrate NHRP into its MPOA Protocol specification [5].  As such,
   NHRP will be used in resolving the ATM addresses of MPOA packets
   destined outside the originating subnet.

3. Key Features

   NHRP provides a mechanism to obtain the NBMA network address of the
   destination, or of a router along the path to the destination. NHRP
   is not a routing protocol, but may make use of routing information.
   This is further discussed in Section 5.

   The most prominent feature of NHRP is that it avoids extra router
   hops in an NBMA with multiple LISs.  To this goal, NHRP provides the
   source with the NBMA address of the destination, if the destination
   is directly attached to the NBMA. If the destination station is not
   attached to the NBMA, then NHRP provides the source with the NBMA
   address of an exit router that has connectivity to the destination.
   In general, there may be multiple exit routers that have connectivity
   to the destination.  If NHRP uses the services of a dynamic routing
   algorithm in fulfilling its function, which is necessary for robust
   and scalable operation, then the exit router identified by NHRP
   reflects the selection made by the network layer dynamic routing
   protocol.  In general, the selection made by the routing protocol
   would often reflect a desirable attribute, such as identifying the
   exit router that induces the least number of hops in the original
   routed path.






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