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Many commonly used network utilities are based on ICMP messages. The [[traceroute]] command can be implemented by transmitting IP datagrams with specially set IP TTL header fields, and looking for ICMP time exceeded in transit and ''[[#Destination unreachable|destination unreachable]]'' messages generated in response. The related [[Ping (networking utility)|ping]] utility is implemented using the ICMP ''echo request'' and ''echo reply'' messages.
ICMP uses the basic support of IP as if it were a higher-level protocol, however, ICMP is actually an integral part of IP. Although ICMP messages are contained within standard IP packets, ICMP messages are usually processed as a special case, distinguished from normal IP processing. In many cases, it is necessary to inspect the contents of the ICMP message and deliver the appropriate [[error message]] to the application responsible for transmitting the IP packet that prompted the ICMP message to be sent.
ICMP is a [[network-layer]] protocol; this makes it a layer 3 protocol in the seven-layer [[OSI model]]. Based on the four-layer TCP/IP model, ICMP is an [[internet-layer]] protocol, which makes it a layer 2 protocol in the [[Internet Standard]] RFC 1122 TCP/IP four-layer model or a layer 3 protocol in the modern five-layer TCP/IP protocol definitions (by Kozierok, Comer, Tanenbaum, Forouzan, Kurose, Stallings).{{Citation needed|date=January 2023}}
There is no port number associated with an ICMP packet, as these numbers are associated with protocols in the [[transport layer]] above, such as TCP and UDP.<ref>{{Cite web | title = The OSI Model's Seven Layers Defined and Functions Explained | work = Microsoft Support | access-date = 2014-12-28 | url = https://support.microsoft.com/kb/103884}}</ref>
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:'''Address mask''' can be set to 0
ICMP Address Mask Request may be used as a part of reconnaissance attack to gather information on the target network, therefore ICMP Address Mask Reply is disabled by default on [[Cisco IOS]].<ref>{{cite web |url=http://www.cisco.com/en/US/docs/ios/12_3/ipaddr/command/reference/ip1_i2g.html#wp1078496 |title=Cisco IOS IP Command Reference, Volume 1 of 4: Addressing and Services, Release 12.3 - IP Addressing and Services Commands: ip mask-reply through ip web-cache |publisher=[[Cisco Systems]] |access-date=2013-01-07 |url-status=dead |archive-url=https://web.archive.org/web/20130102124241/http://www.cisco.com/en/US/docs/ios/12_3/ipaddr/command/reference/ip1_i2g.html#wp1078496 |archive-date=2013-01-02 }}</ref>
===Address mask reply===
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