Chapter 11. ICMP: Internet Control Message Protocol

11.1. Introduction

ICMP communicates error and administrative messages between IP systems and is an integral and required part of any IP implementation. The specification for ICMP appears in RFC 792 [Postel 1981b]. RFC 950 [Mogul and Postel 1985] and RFC 1256 [Deering 1991a] define additional ICMP message types. RFC 1122 [Braden 1989a] also provides important details on ICMP.

ICMP has its own transport protocol number (1) allowing ICMP messages to be carried within an IP datagram. Application programs can send and receive ICMP messages directly through the raw IP interface discussed in Chapter 32.

We can divide the ICMP messages into two classes: errors and queries. Query ...

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