TYPE message type
CODE (sent by):

0 = Echo Reply .
0 = (no special meaning) (host, router)

3 = Destination Unreachable .
0 = network unreachable (router)
1 = host unreachable (router)
2 = protocol unreachable (host)
3 = port unreachable (host)
4 = fragmentation needed but impossible
     because of "don't fragment" command (router)
5 = source route not reachable (router)

4 = Source Quench .
0 = datagram could not be received host, router or routed

5 = Redirect .
    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)

8 = Echo Request .
0 = (no special meaning) (host, router)

11 = Time Exceeded .
0 = TTL set to 0 (router)
1 = reassembly timer exceeded (host)

12 = Parameter Problem .
0 = the ICMP header's pointer identifies
     a faulty octett within the datagram (host, router)

13 = Timestamp Request .
0 = (no special meaning) (host, router)

14 = Timestamp Reply .
0 = (no special meaning) (host, router)

15 = Information Request .
0 = (no special meaning) (host, router)

16 = Information Reply .
0 = (no special meaning) (host, router)

A1 = Address Format Request .
0 = (no special meaning) (host, router)

A2 = Address Format Reply .
n = [number of bits in a subnet mask] (host, router)