ICMP Message Types

Echo Reply

ICMP Type 0 Echo Reply is sent in response to an Echo Request (Type 8).

Echo Request

ICMP Type 8 Echo Request is the outbound half of the ping mechanism.

Timestamp

ICMP Type 13 Timestamp is a request for a timestamp from a remote host, used to measure one-way delay and clock offset between hosts.

Timestamp Reply

ICMP Type 14 Timestamp Reply is sent in response to a Timestamp Request (Type 13).

Destination Unreachable

ICMP Type 3 Destination Unreachable is sent by a router or host when a packet cannot be delivered.

Time Exceeded

ICMP Type 11 Time Exceeded is sent when a packet is discarded because its TTL (Time to Live) reached zero in transit.

Parameter Problem

ICMP Type 12 Parameter Problem is sent when a router or host encounters an error in an IP header that prevents it from processing the packet.

Redirect

ICMP Type 5 Redirect is sent by a router to inform a host that a better route exists for a destination.

Router Advertisement

ICMP Type 9 Router Advertisement is sent by routers to announce their presence and IP addresses to hosts on a subnet.

Router Solicitation

ICMP Type 10 Router Solicitation is sent by a host to request immediate Router Advertisement messages from all routers on the subnet.

Photuris

ICMP Type 40 Photuris carries security failure notifications for the Photuris session-key management protocol (RFC 2521).

Extended Echo Request

ICMP Type 42 Extended Echo Request allows a host to query the operational status of a specific network interface by name, index, or address – without requiring layer-2 connectivity to that interface.

Extended Echo Reply

ICMP Type 43 Extended Echo Reply responds to an Extended Echo Request (Type 42) with the operational status of the queried network interface.