| Code | Description |
| 0 | Network unreachable error. |
| 1 | Host unreachable error. |
| 2 | Protocol unreachable error (the designated transport protocol is not supported). |
| 3 | Port unreachable error (the designated protocol is unable to inform the host of the incoming message). |
| 4 | The datagram is too big. Packet fragmentation is required but the 'don't fragment' (DF) flag is on. |
| 5 | Source route failed error. |
| 6 | Destination network unknown error. |
| 7 | Destination host unknown error. |
| 8 | Source host isolated error (military use only). |
| 9 | The destination network is administratively prohibited. |
| 10 | The destination host is administratively prohibited. |
| 11 | The network is unreachable for Type Of Service. |
| 12 | The host is unreachable for Type Of Service. |
| 13 | Communication administratively prohibited (administrative filtering prevents packet from being forwarded). |
| 14 | Host precedence violation (indicates the requested precedence is not permitted for the combination of host or network and port). |
| 15 | Precedence cutoff in effect (precedence of datagram is below the level set by the network administrators). |