RFC 2583 (rfc2583) - Page 1 of 9
Guidelines for Next Hop Client (NHC) Developers
Alternative Format: Original Text Document
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