ICMP

(Basic Internet Control Message Protocol Packet format)

see also:

Internet Control Message Protocol Parameter Problems packet format (Type 12)
Internet Control Message Protocol Echo Request/Echo Reply packet format (Types 8/0)
Internet Control Message Protocol Router Advertisement (Type 9)
Internet Control Message Protocol Timestamp/Timestamp Reply packet format (Types 13 & 14)
Internet Control Message Protocol Address Mask Request/Reply (Types 17 & 18)

 

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
Type Code ICMP header checksum
Other message-specific information...(depending on T&C)

ICMP header immediately follows IP header

Type Name/Codes (Code=0 unless otherwise specified)

0 Echo Reply
3 Destination Unreachable
  0 Net Unreachable
  1 Host Unreachable
  2 Protocol Unreachable
  3 Port Unreachable
  4 Fragmentation Needed & 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 Message
  0 Redirect Datagram for the Network
  1 Redirect Datagram for the Host
  2 Redirect Datagram for the TOS & Network
  3 Redirect Datagram for the TOS & Host
6 Alternative Host Address
7 Reserved
8 Echo
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
19 reserved for security
20-29 reserved
30 Traceroute
31-41 various services
42-255 reserved