Field: code
Length: 1 byte
Contents: contents of message.
TYPE = 0 - Echo Reply sent by:
0 = (no special meaning) host, router
TYPE = 3 - Destination Unreachable sent by:
0 = network unreachable router
1 = host unreachable router
2 = protocol unreachable host
3 = port unreachable host
4 = fragmentation needed but impossible router
because of 'don't fragment' command
5 = source route not reachable router
TYPE = 4 - Source Quench sent by:
0 = datagram could not be received host, router
or routed
TYPE = 5 - Redirect sent by:
redirection of all datagrams ...
0 = ...to a specific IP network router
1 = ...to a specific IP host router
2 = ...of a spedific type of service and network router
3 = ...of a specific type of service and host router
TYPE = 8 - Echo Request sent by:
0 = (no special meaning) host, router
TYPE = 11 - Time Exceeded sent by:
0 = TTL set to 0 router
1 = reassembly timer exceeded host
0 = the ICMP header's pointer identifies host, router
a faulty octett within the datagram
TYPE = 13/14 - Timestamp Request/Reply sent by:
0 = (no special meaning) host, router
TYPE = 15/16 - Information Request/Reply sent by:
0 = (no special meaning) host, router
TYPE = A1 - Address Format Request sent by:
0 = (no special meaning) host, router
TYPE = A2 - Address Format Reply sent by:
n = [number of bits in a subnet mask] host, router