Overview
ISO 9542:1988 specifies the End System to Intermediate System routeing exchange protocol for use with ISO 8473 (the connectionless-mode Network Service). It defines how Network Layer entities in End Systems (ES) and Intermediate Systems (IS) exchange configuration and routing information on a shared subnetwork. The protocol is connectionless and intended to minimize the amount of a priori state, memory and computational complexity required by End Systems while enabling dynamic discovery of reachable IS/ES peers.
Key topics and technical requirements
- Scope and purpose: Procedures for exchanging configuration and routing data between ES and IS entities to support forwarding of NPDUs (Network Protocol Data Units).
- Protocol functions: Mechanisms for ES discovery of ISs, IS discovery of ESs, and route redirection to indicate better forwarding paths.
- PDU structure and encoding: Definition of Protocol Data Units (PDUs) and field encodings used for messages such as End System Hello (ESH), Intermediate System Hello (ISH) and Redirect (RD) PDUs.
- Underlying service assumptions: Designed to operate over a connectionless subnetwork service (see ISO 8473); supports broadcast, multicast or multi-destination addressing where available.
- Subnetwork types: Clarifies behavior on point-to-point, broadcast (e.g., LAN), and general-topology subnetworks and how multi-destination addresses are handled.
- Protocol control and timers: Rules for interpreting control information and parameters (e.g., holding times, suggested configuration timers) and for conformance testing.
- Conformance and testing: Functional requirements for implementations, PICS proformas and informative annexes (supporting technical material and state tables).
Practical applications and users
ISO 9542 is relevant when implementing OSI Network Layer routing between end hosts and local routers (Intermediate Systems). Typical users include:
- Network protocol engineers implementing OSI/CLNS (Connectionless-mode Network Service) stacks
- Network equipment vendors designing routers, gateways and LAN interface firmware
- Systems integrators and testers validating conformance to OSI Network Layer routing behavior
- Network architects who need to support ES discovery, local redirection and efficient route selection on LANs or other subnetworks
- Academic and standards researchers working on legacy OSI protocol suites
Related standards
- ISO 8473 - Protocol for providing the connectionless-mode Network Service (required companion)
- ISO 7498 and addenda - OSI Basic Reference Model
- ISO 8348 and addenda - Network Service Definition and addressing
- ISO 8802 - Local Area Networks (used for broadcast subnetworks)
- ISO 8208, ISO 8648, and CCITT X.25 - referenced for subnetwork and packet service assumptions
Keywords: ISO 9542:1988, End System to Intermediate System, routing exchange protocol, ISO 8473, connectionless-mode network service, ES/IS routing, PDUs, OSI Network Layer.