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Internet Control Message Protocol (RFC0777)

IP.com Disclosure Number: IPCOM000003825D
Original Publication Date: 1981-Apr-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 10 page(s) / 19K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

J. Postel: AUTHOR

Abstract

The Internet Protocol (IP) [1] is used for host-to-host datagram service in a system of interconnected networks called the Catenet [2]. The network connecting devices are called Gateways. These gateways communicate between themselves for control purposes via a Gateway to Gateway Protocol (GGP) [3,4]. Occasionally a gateway or destination host will communicate with a source host, for example, to report an error in datagram processing. For such purposes this protocol, the Internet Control Message Protocol (ICMP), is used. ICMP, uses the basic support of IP as if it were a higher level protocol, however, ICMP is actually an integral part of IP, and must be implemented by every IP module.

This text was extracted from a ASCII Text document.
This is the abbreviated version, containing approximately 16% of the total text.

Network Working Group J. Postel

Request for Comments: 777 ISI

April 1981

Updates: IENs 109, 128

Updates: RFC 760

Internet Control Message Protocol

Introduction

The Internet Protocol (IP) [1] is used for host-to-host datagram

service in a system of interconnected networks called the

Catenet [2]. The network connecting devices are called Gateways.

These gateways communicate between themselves for control purposes

via a Gateway to Gateway Protocol (GGP) [3,4]. Occasionally a

gateway or destination host will communicate with a source host, for

example, to report an error in datagram processing. For such

purposes this protocol, the Internet Control Message Protocol (ICMP),

is used. ICMP, uses the basic support of IP as if it were a higher

level protocol, however, ICMP is actually an integral part of IP, and

must be implemented by every IP module.

ICMP messages are sent in several situations: for example, when a

datagram cannot reach its destination, when the gateway does not have

the buffering capacity to forward a datagram, and when the gateway

can direct the host to send traffic on a shorter route.

The Internet Protocol is not designed to be absolutely reliable. The

purpose of these control messages is to provide feedback about

problems in the communication environment, not to make IP reliable.

There are still no guarantees that a datagram will be delivered or a

control message will be returned. Some datagrams may still be

undelivered without any report of their loss. The higher level

protocols that use IP must implement their own reliability procedures

if reliable communication is required.

The ICMP messages typically report errors in the processing of

datagrams, to avoid the infinite regress of messages about messages

etc., no ICMP messages are sent about ICMP messages.

Message Formats

ICMP messages are sent using the basic IP header. The first octet of

the data portion of the datagram is a ICMP type field; the value of

this field determines the format of the remaining data. Any field

labeled "unused" is reserved for later extensions and must be zero

when sent, but receivers should not check these fields. Unless

otherwise noted under the individual format descriptions, the values

of the internet header fields are as follows:

April 1981

RFC 777

Version

4

IHL

Internet header length in 32-bit words.

Type of Service

0

Total Length

Length of internet header and data in octets.

Identification, Flags, Fragment Offset

Used in fragmentation, see [1].

Time to Live

Time to live in seconds; as this field is decremented at each

machine in which the datagram is processed, the value in this

field should be at least as ...