RFC 792

RFC 792
Title	Internet Control Message Protocol
Number	792
Author	Jon Postel
Year	1981
Status	Standard
Pages	26

RFC 792

Overview

RFC 792 defines the Internet Control Message Protocol as the diagnostic and error-reporting companion to the Internet Protocol, specifying message semantics for hosts and gateways. It situates the protocol within the TCP/IP suite alongside Transmission Control Protocol, User Datagram Protocol, Internet Protocol, ARPANET, and DARPA research efforts. The memo establishes procedures used by systems such as UNIX, VAX, BSD implementations and early Cisco Systems routers for reporting unreachable destinations, redirecting routes, and probing connectivity.

History and Development

The document was authored during the era of the ARPANET to formalize operational practices that had emerged in experimental networks developed by University of California, Los Angeles, Stanford Research Institute, MIT, and Stanford University. The work reflects coordination among contributors linked to USC Information Sciences Institute and individuals associated with the Internet Engineering Task Force predecessor activities. RFC 792 built on earlier memos that defined Internet Protocol Version 4 behavior and paralleled contemporaneous specifications like RFCs authored by Jon Postel and standards discussed at IETF workshops and IAB meetings.

Protocol Specification

RFC 792 specifies message types and codes to report network errors and operational information for IPv4 networks. The specification references addressing and fragmentation behavior described in contemporaneous protocols implemented on systems such as DEC, Sun Microsystems, Intel, IBM network stacks. It defines interactions with routing components including behavior expected of hosts, gateways, and devices from vendors like Nortel and 3Com operating in internets constructed with routing protocols that later influenced Routing Information Protocol and Open Shortest Path First design discussions.

Packet Format and Message Types

The memo details the ICMP packet header fields and the canonical formats for messages such as Destination Unreachable, Source Quench, Redirect, Echo, Echo Reply, Time Exceeded, Parameter Problem, and Timestamp messages. Implementations in stacks for platforms like BSD and System V mapped these types to specific handling paths in network daemons and utilities such as ping and traceroute which were developed at institutions like UC Berkeley and MIT. The format includes an 8-byte header, type and code values, checksum, and encapsulates portions of the triggering IPv4 datagram, consistent with practices in early Internet Assigned Numbers Authority allocations and packet capture tools used in research at LBNL.

Implementation and Usage

RFC 792's conventions were implemented in commercial and academic routers and hosts from vendors and projects including Cisco Systems, Sun Microsystems, DEC, Hewlett-Packard, and academic distributions emerging from UC Berkeley Computer Systems Research Group. Network diagnostic tools such as ping and traceroute rely on ICMP Echo and Time Exceeded behaviors specified by the memo, and network management suites from companies like IBM and HP incorporated its semantics into monitoring. The protocol influenced middleboxes and firewalls produced by vendors like Checkpoint and later managed by organizations including IETF working groups for operational guidance.

Security and Vulnerabilities

Over time, implementers observed that ICMP message types could be exploited for reconnaissance, denial-of-service, and path manipulation; attacks leveraged behaviors described in the specification against systems by entities associated with threat research at institutions like SRI International and commercial security firms such as Symantec and McAfee. Notable operational mitigations recommended by network operators from ARIN and administrators at service providers such as AT&T and Verizon included rate limiting and selective ICMP filtering implemented in devices from Cisco Systems and Juniper Networks. The security posture evolved through discussions in IETF security-oriented working groups and advisories produced by CERT Coordination Center.

Impact and Legacy

RFC 792 established foundational diagnostics and error-reporting mechanisms that shaped later standards, influencing ICMPv6 work led by groups tied to IETF and IAB and informing extensions in standards bodies including IEEE. Its packet semantics remain integral to network troubleshooting used in operational environments at organizations like Google, Amazon, Microsoft, and academic networks run by institutions such as Stanford University and MIT. The memo's influence is evident in the persistence of echo-based tools and in architectural discussions archived by RFC Editor collections and historical retrospectives at research centers like USC Information Sciences Institute.

Category:Internet standards