ICMP Router Discovery Messages
RFC 1256
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RFC - Proposed Standard
(September 1991; No errata)
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Author |
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Steve Deering
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Last updated |
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2013-03-02
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IETF
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(None)
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IESG |
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RFC 1256 (Proposed Standard)
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Network Working Group S. Deering, Editor
Request for Comments: 1256 Xerox PARC
September 1991
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.
Abstract
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
References 18
Author's Address 19
1. Terminology
The following terms have a precise meaning when used in this
document:
system a device that implements the Internet Protocol, IP [9].
router a system that forwards IP datagrams, as specified
Router Discovery Working Group [Page 1]
RFC 1256 ICMP Router Discovery Messages September 1991
in [2]. 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
options.
host any system that is not a router.
multicast unless otherwise qualified, means the use of either IP
multicast [4] or IP broadcast [6] 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
this. Examples of links are LANs (possibly bridged to
other LANs), wide-area store-and-forward networks,
satellite channels, and point-to-point links.
multicast link
a link over which IP multicast or IP broadcast service
is supported. This includes broadcast media such as
LANs and satellite channels, single point-to-point
links, and some store-and-forward networks such as SMDS
networks [8].
interface a system's attachment point to a link. It is possible
(though unusual) for a system to have more than one
interface to the same link. Interfaces are uniquely
identified by IP unicast addresses; a single interface
may have more than one such address.
multicast interface
an interface to a multicast link, that is, an interface
to a link over which IP multicast or IP broadcast
service is supported.
subnet either a single subnet of a subnetted IP network [7] or
a single non-subnetted IP network, i.e., the entity
identified by an IP address logically ANDed with its
assigned subnet mask. More than one subnet may exist
on the same link.
neighboring having an IP address belonging to the same subnet.
Router Discovery Working Group [Page 2]
RFC 1256 ICMP Router Discovery Messages September 1991
2. Protocol Overview
Before a host can send IP datagrams beyond its directly-attached
subnet, it must discover the address of at least one operational
router on that subnet. Typically, this is accomplished by reading a
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