ICMP Type Numbers
According to WIKIPEDA ICMP The Internet Control Message Protocol is part of the Internet Protocol Suite, as defined in RFC 792. ICMP messages are typically used for diagnostic or control purposes or generated in response to errors in IP operations (as specified in RFC 1122). ICMP errors are directed to the source IP address of the originating packet.
The Internet Control Message Protocol (ICMP) is one of the main protocols of the internet protocol suite. It is used by network devices, like routers, to send error messages indicating, for example, that a requested service is not available or that a host or router could not be reached. ICMP can also be used to relay query messages.[1] It is assigned protocol number 1.[2] ICMP[3] differs from transport protocols such as TCP and UDP in that it is not typically used to exchange data between systems, nor is it regularly employed by end-user network applications (with the exception of some diagnostic tools like ping and traceroute).
ICMP Header
Description of ICMP types :
| Code | Descriton | RFC |
| 0 | Net Unreachable | [RFC792] |
| 1 | Host Unreachable | [RFC792] |
| 2 | Protocol Unreachable | [RFC792] |
| 3 | Port Unreachable | [RFC792] |
| 4 | Fragmentation Needed and Don't Fragment was Set | [RFC792] |
| 5 | Source Route Failed | [RFC792] |
| 6 | Destination Network Unknown | [RFC1122] |
| 7 | Destination Host Unknown | [RFC1122] |
| 8 | Source Host Isolated | [RFC1122] |
| 9 | Communication with Destination Network is Administratively Prohibited | [RFC1122] |
| 10 | Communication with Destination Host is Administratively Prohibited | [RFC1122] |
| 11 | Destination Network Unreachable for Type of Service | [RFC1122] |
| 12 | Destination Host Unreachable for Type of Service | [RFC1122] |
| 13 | Communication Administratively Prohibited | [RFC1812] |
| 14 | Host Precedence Violation | [RFC1812] |
| 15 | Precedence cutoff in effect | [RFC1812] |
