a icmp header:

        0                                             15 16                                            31
       --------------------------------------------------------------------------------------------------
       |         type           |         code          |                 checksum                      |
       |                        |                       |                                               |
       --------------------------------------------------------------------------------------------------
       |                                   dependent on type and code                                   |
       |                                                                                                |
       --------------------------------------------------------------------------------------------------

       
        0 Echo Reply
        3 Destination Unreachable
              0 Net Unreachable
              1 Host Unreachable
              2 Protocol Unreachable
              3 Port Unreachable
              4 Fragmentation Needed and DF Set
              5 Source Route Failed
              6 Destination Network Unknown
              7 Destination Host Unknown
              8 Source Host Isolated
              9 Network Administratively Prohibited
             10 Host Administratively Prohibited
             11 Network Unreachable for TOS
             12 Host Unreachable for TOS
             13 Communication Administratively Prohibited
        4 Source Quench
        5 Redirect
              0 Redirect Datagram for the Network
              1 Redirect Datagram for the Host
              2 Redirect Datagram for the TOS and Network
              3 Redirect Datagram for the TOS and Host
        8 Echo Request
        9 Router Advertisement
       10 Router Selection
       11 Time Exceeded
              0 Time to Live exceeded in transit
              1 Fragment Reassembly Time exceeded
       12 Parameter Problem
              0 Pointer indicates the error
              1 Missing a required option
              2 Bad length
       13 Timestamp
       14 Timestamp Reply
       15 Information Request
       16 Information Reply
       17 Address Mask Request
       18 Address Mask Reply
       30 Traceroute