ICMP message types
ICMPv4 uses different types of messages. ICMP messages are identified by the "Type" field in ICMPv4 header. ICMPv4 header has a "Code" field also. The Type field in ICMPv4 header determines what the ICMP packet is used for. The Code field contains additional information related with Type field.
Following table lists some important ICMPv4 message types.
| ICMP Message Type number | ICMP Message Type | Description |
|---|---|---|
| 0 and 8 | Echo Request/Echo Reply | ICMP Echo/Echo Reply type of messages are used by uilities like Ping, Tracert, Pathping etc. These tools are mainly used for network troubleshooting. |
| 3 | Destination Unreachable | ICMP Destination unreachable type of messages are used by computers or routers to inform the sender that the destination is unreachable. Reason why unreachable also may be included. |
| 4 | Source Quench | ICMP Source Quench type of messages allows to inform a sending computer to drcrease its sending rate to ease congestion. Deprecated. |
| 5 | Redirect | ICMP redirect type of messages allows a router on a nonoptimal route between sender and receiver to redirect traffic via a better path. |
| 9 | Router Advertisement | ICMP Router Advertisement type of messages allows routers to advertise their presence to computers in a network segment. Computers discover the addresses of the routers by listening Router Advertisement messages. |
| 10 | Router Solicitation | ICMP Router Solicitation type of messages are used by computers in a network segment for immediate Router Advertisement messages. |
| 11 | Time Exceeded | ICMP Time Exceeded type of messages are used to indicate that the IP datagram’s Time-to-Live (TTL) value value has exceeded or fragment reassmbly timer timed out. |
| 12 | Parameter Problem | ICMP Parameter Problem message allows to inform thet some error happened while processing the IPv4 datagram. |
| 13 and 14 | ICMP Timestamp Request and Timestamp Reply messages | ICMP Timestamp Request and Timestamp Reply messages are used by network devices to synchronize their system clock. |
| 40 | Photuris | ICMP Photuris messages used to communicate messages related with Photuris security protocol. |
Following tables shows some ICMP message Type numbers. Please note that some are deprecated and some other are related with IPv6.
| ICMP Type number | Description | Status | Related RFC |
|---|---|---|---|
| 0 | Echo Reply | RFC 792 | |
| 1-2 | Unassigned | ||
| 3 | Destination Unreachable | RFC 792 | |
| 4 | Source Quench | Deprecated | RFC 792 |
| 5 | Redirect | RFC 792 | |
| 6 | Alternate Host Address | Deprecated | |
| 7 | Unassigned | ||
| 8 | Echo | RFC 792 | |
| 9 | Router Advertisement | RFC 1256 | |
| 10 | Router Solicitation | RFC 1256 | |
| 11 | Time Exceeded | RFC 792 | |
| 12 | Parameter Problem | RFC 792 | |
| 13 | Timestamp | RFC 792 | |
| 14 | Timestamp Reply | RFC 792 | |
| 15 | Information Request | Deprecated | RFC 792 |
| 16 | Information Reply | Deprecated | RFC 792 |
| 17 | Address Mask Request | Deprecated | RFC 950 |
| 18 | Address Mask Reply | Deprecated | RFC 950 |
| 19-29 | Reserved | ||
| 30 | Traceroute | RFC 1393 | |
| 31 | Datagram Conversion Error | Deprecated | RFC 1475 |
| 32 | Mobile Host Redirect | Deprecated | |
| 33 | IPv6 Where-Are-You | Deprecated | |
| 34 | IPv6 I-Am-Here | Deprecated | |
| 35 | Mobile Registration Request | Deprecated | |
| 36 | Mobile Registration Reply | Deprecated | |
| 37 | Domain Name Request | Deprecated | |
| 38 | Domain Name Reply | Deprecated | |
| 39 | SKIP | Deprecated | |
| 40 | Photuris | RFC 2521 | |
| 41 | Experimental | ||
| 42-252 | Unassigned | ||
| 253-254 | Reserved | RFC 4727 |