Internet Control Message Protocol message types

ICMP sends and receives these message types.

Item	Description
echo request	Sent by hosts and gateways to test whether a destination is alive and reachable.
information request	Sent by hosts and gateways to obtain an Internet address for a network to which they are attached. This message type is sent with the network portion of IP destination address set to a value of 0.
timestamp request	Sent to request that the destination machine return its current value for time of day.
address mask request	Sent by host to learn its subnet mask. The host can either send to a gateway, if it knows the gateway address, or send a broadcast message.
destination unreachable	Sent when a gateway cannot deliver an IP datagram.
source quench	Sent by discarding machine when datagrams arrive too quickly for a gateway or host to process, in order to request that the original source slow down its rate of sending datagrams.
redirect message	Sent when a gateway detects that some host is using a nonoptimum route.
echo reply	Sent by any machine that receives an echo request in reply to the machine which sent the request.
information reply	Sent by gateways in response to requests for network addresses, with both the source and destination fields of the IP datagram specified.
timestamp reply	Sent with current value of time of day.
address mask reply	Sent to machines requesting subnet masks.
parameter problem	Sent when a host or gateway finds a problem with a datagram header.
time exceeded	Sent when the following are true: Each IP datagram contains a time-to-live counter (hop count), which is decremented by each gateway. A gateway discards a datagram because its hop count has reached a value of 0.
Internet Timestamp	Used to record the time stamps through the route.