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Is the ICMP protocol generally used in real world networking configurations ?

  • If yes, what are some real world examples that make use of this protocol.

In addition, I see that the ICMP echo requests (type 0 / 8) are a must filter within an organization be it small or large, and the main reason is to avoid foot printing of the network by potential malicious persons.

  • In reality does this must be mandatory for a network and does it happen ? I see large sites as google, yahoo and other sites not blocking ICMP echo messages.

Regards

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    ICMP echo is one small part of ICMP that is an integral part of IP. – Ron Maupin Mar 30 at 16:42
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    They do block some ICMP messages. It's a tradeoff between usability and security. You may block echo requests inbound, but allow echo replies inbound. – Ron Trunk Mar 30 at 16:42
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Completely filtering ICMP, as some people do, is a very bad idea. It is designed to give feedback to applications and users. For example, a network or destination host that does not exist can generate an ICMP error message. It is an integral part of IP, and is used for PMTUD. See RFC 792, Internet Message Control Protocol.

IPv6 relies heavily on ICMP, and there is RFC 4890, Recommendations for Filtering ICMPv6 Messages in Firewalls that explains what should and should not be blocked for ICMPv6.

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