ICMP message types of interest from a remote security assessment perspective are listed in Table A-3. Both the message types and individual codes are listed, along with details of RFCs and other standards in which these message types are discussed.
Table A-3. ICMP message types
| Type | Code | Notes |
|---|
| 0 | 0 | Echo reply (RFC 792) |
| 3 | 0 | Destination network unreachable |
| 3 | 1 | Destination host unreachable |
| 3 | 2 | Destination protocol unreachable |
| 3 | 3 | Destination port unreachable |
| 3 | 4 | Fragmentation required, but don't fragment bit was set |
| 3 | 5 | Source route failed |
| 3 | 6 | Destination network unknown |
| 3 | 7 | Destination host unknown |
| 3 | 8 | Source host isolated |
| 3 | 9 | Communication with destination network is administratively prohibited |
| 3 | 10 | Communication with destination host is administratively prohibited |
| 3 | 11 | Destination network unreachable for type of service |
| 3 | 12 | Destination host unreachable for type of service |
| 3 | 13 | Communication administratively prohibited (RFC 1812) |
| 3 | 14 | Host precedence violation (RFC 1812) |
| 3 | 15 | Precedence cutoff in effect (RFC 1812) |
| 4 | 0 | Source quench (RFC 792) |
| 5 | 0 | Redirect datagram for the network or subnet |
| 5 | 1 | Redirect datagram for the host |
| 5 | 2 | Redirect datagram for the type of service and network |
| 5 | 3 | Redirect datagram for the type of service and host |
| 8 | 0 | Echo request (RFC 792) |
| 9 | 0 | Normal router advertisement (RFC 1256) |
| 9 | 16 | Does not route common traffic (RFC 2002) |
| 11 | 0 | Time to live (TTL) exceeded in transit (RFC 792) |
| 11 | 1 | Fragment reassembly time exceeded (RFC 792) |
| 13 | 0 | Timestamp request (RFC 792) |
| 14 | 0 | Timestamp reply (RFC 792) |
| 15 | 0 | Information request (RFC 792) |
| 16 | 0 | Information reply (RFC 792) |
| 17 | 0 | Address mask request (RFC 950) |
| 18 | 0 | Address mask reply (RFC 950) |
| 30 | 0 | Traceroute (RFC 1393) |
