What is the functional characteristics of ICMP,ICMP

　　ICMP is an Internet Control Messaging Protocol (PROTOCOL). It is a child protocol of the TCP/IP protocol family that is used to pass control messages between IP hosts and routers. Control message refers to network communication, whether the host is up to, whether the route is available or not. Although these control messages do not transmit user data, they play an important role in the transfer of user data.

　　The function and characteristics of ICMP

　　The characteristics of ICMP:

ICMP itself is a protocol of the network layer;

The ICMP error report uses the router-source host mode, and the router reports the error reason only to the source host when it finds the datagram transmission errors;

ICMP does not guarantee that all IP datagrams can be transmitted to the destination host;

ICMP does not correct errors, it only reports errors. Error handling needs to be done by a high-level agreement.

ICMP message type

　　ICMP error control

ICMP error report message:

Destination station not up to:

Source Station Suppression

Timeout

Parameter problem

Changing routes

Destination Station not reachable

Network unreachable (NET unreachable)

Hosts unreachable (host unreachable)

Protocol unreachable (Protocol unreachable)

Ports unreachable (Port unreachable)

Source route selection cannot be completed (Route failed)

Destination network agnostic (unknown Destination network)

Destination host is not known (unknown destination host)