ICMP Message Type

Type code type description

0 response (echo-reply)
3 inaccessible
4. Source Suppression
5 redirection
8. Response Request)
11 timeout
12 parameter failure
13. Timestamp Request
14 timestamp response
15. Information Request (* expired)
16. Information Response (* expired)
17. Address Mask Request
18 Address Mask response

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Appendix:

Several common ICMP messages:

1. Response RequestThe most commonly used Ping is the Response Request (type = 8) and response (type = 0). A host sends an ICMP packet of type = 8 to a node, if there is no exception on the way (for example, discarded by the router, the target does not respond to ICMP or the transmission fails), the target returns an ICMP message of type = 0, indicating that this host exists, more detailed tracert uses the node used to calculate ICMP packets to determine the network distance between the host and the target.2. The target cannot be reached, the source is blocked, and the report is received.The format of the three types of packets is the same. The type of the destination inaccessible packet (type = 3) is used when the router or host cannot transmit data reports, for example, if we want to connect to a non-existent system Port (port number less than 1024) of the other party, the ICMP packet of type = 3 and code = 3 will be returned. It will tell us: "Hey, don't connect. I'm not at home! ", Common types of unattainable include unattainable Network (code = 0), unattainable host (code = 1), and unattainable protocol (code = 2. Source suppression acts as a traffic control role, which notifies the host to reduce the datagram traffic. Because ICMP does not resume the transmission of packets, as long as the packets are stopped, the host will gradually resume the transmission rate. Finally, a non-connection network problem is that the data packet will be lost, or the target cannot be found after a long time wandering in the network, or the host cannot reorganize the data packet segment due to congestion, in this case, the generation of ICMP timeout packets is triggered. The code field of the timeout message has two values: code = 0 indicates the transmission has timed out, and code = 1 indicates the reorganization segment has timed out.3. TimestampThe timestamp request message (type = 13) and timestamp Response Message (type = 14) are used to test the time at which the datagram is transmitted back and forth between two hosts. During transmission, the host fills in the original timestamp. After receiving the request, the receiver fills in the received Timestamp and returns it in the message format of type = 14. The sender calculates the time difference. Some systems do not respond to such messages.

ICMP Message Type