RFC 2583 (rfc2583) - Page 1 of 9

Guidelines for Next Hop Client (NHC) Developers

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Network Working Group                                       R. Carlson
Request for Comments: 2583                                         ANL
Category: Informational                                     L. Winkler
                                                                   ANL
                                                              May 1999


            Guidelines for Next Hop Client (NHC) Developers

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

1. Abstract

   This document provides guidelines for developers of the Next Hop
   Resolution Protocol Clients (NHC).  It assumes that the clients are
   directly connected to an ATM based NBMA network.  The same principles
   will apply to clients connected to other types of NBMA networks.  The
   intent is to define the interaction between the NHC code and the
   TCP/IP protocol stack of the local host operating system.  The NHC is
   capable of sending NHRP requests to a Next Hop Resolution Protocol
   Server (NHS) to resolve both inter and intra LIS addresses.  The NHS
   reply may be positive (ACK) indicating a short-cut path is available
   or negative (NAK) indicating that a shortcut is not available and the
   routed path must be used.  The NHC must cache (maintain state) for
   both the ACK and NAK replies in order to use the correct shortcut or
   routed path.  The NAK reply must be cached to avoid making repeated
   requests to the NHS when the routed path is being used.

2. Overview

   In the Classical IP over ATM model [1], an ATM attached host
   communicates with an ATMARP server to resolve IP to ATM address
   semantics.  This model supports the concept of a Logical IP Subnet
   (LIS) with intra LIS communications using direct PVCs/SVCs and inter
   LIS communications using IP routers to forward packets.  This model
   easily maps to the conventional LAN model of subnets and routers.
   The Next Hop Resolution Protocol (NHRP) [2] defines how the LIS model
   can be modified to allow direct ATM SVCs (shortcut paths) for inter
   LIS traffic.  With NHRP, nodes directly attached to an ATM network
   can bypass the IP routers and establish a direct switched virtual



Carlson & Winkler            Informational
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