ICMP is an auxiliary protocol, which provides routing, diagnostic and error functionality for IP. It is described in [INTERNET:8]. A router MUST support ICMP.
ICMP messages are grouped in two classes that are discussed in the following sections:
ICMP error messages:
Destination Unreachable Section 184.108.40.206 Redirect Section 220.127.116.11 Source Quench Section 18.104.22.168 Time Exceeded Section 22.214.171.124 Parameter Problem Section 126.96.36.199 ICMP query messages: Echo Section 188.8.131.52 Information Section 184.108.40.206 Timestamp Section 220.127.116.11 Address Mask Section 18.104.22.168 Router Discovery Section 22.214.171.124General ICMP requirements and discussion are in the next section.