ICMP Router Discovery Messages (RFC1256)
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2000-Sep-12
Internet Society Requests For Comment (RFCs)
This document specifies an extension of the Internet Control Message Protocol (ICMP) to enable hosts attached to multicast or broadcast networks to discover the IP addresses of their neighboring routers.
Network Working Group S. Deering, Editor
Request for Comments: 1256 Xerox PARC
ICMP Router Discovery Messages
Status of this Memo
This RFC specifies an IAB standards track protocol for the Internet
community, and requests discussion and suggestions for improvements.
Please refer to the current edition of the "IAB Official Protocol
Standards" for the standardization state and status of this protocol.
This document is a product of the IETF Router Discovery Working
Group. Distribution of this memo is unlimited.
This document specifies an extension of the Internet Control Message
Protocol (ICMP) to enable hosts attached to multicast or broadcast
networks to discover the IP addresses of their neighboring routers.
Table of Contents
1. Terminology 1
2. Protocol Overview 3
3. Message Formats 5
4. Router Specification 7
4.1. Router Configuration Variables 7
4.2. Message Validation by Routers 9
4.3. Router Behavior 9
5. Host Specification 12
5.1. Host Configuration Variables 12
5.2. Message Validation by Hosts 13
5.3. Host Behavior 14
6. Protocol Constants 17
7. Security Considerations 17
Author's Address 19
The following terms have a precise meaning when used in this
system a device that implements the Internet Protocol, IP .
router a system that forwards IP datagrams, as specified
in . This does not include systems that, though
capable of IP forwarding, have that capability turned
off. Nor does it include systems that do IP forwarding
only insofar as required to obey IP Source Route
host any system that is not a router.
multicast unless otherwise qualified, means the use of either IP
multicast  or IP broadcast  service.
link a communication facility or medium over which systems
can communicate at the link layer, i.e., the protocol
layer immediately below IP. The term "physical
network" has sometimes been used (imprecisely) for