Icmp:internet Control Message Protocol

ICMP is (Internet Control message Protocol) Internet Controlled message protocol. It is an IP layer sub-protocol of the TCP/IP protocol family that is used to pass control messages between IP hosts and routers. The control message refers to the message that the network is not accessible, whether the host is available, whether the route is available, and so on. These control messages, while not transmitting user data, play an important role in the delivery of user data.

ICMP is located in the IP layer of the TCP/IP protocol family.

The main features of ICMP include: Verifying that the IP packet is successfully delivered to the destination address, notifying the specific reasons for the IP packet being discarded during the sending process, and improving the network settings. At the same time, this notification message for ICMP is sent using IP, and the host of the ICMP packet is received to decompose the ICMP header and data and to know the cause of the specific occurrence.

The first 4 bytes of the ICMP message are the same, but the remaining bytes are different.

The Type field can have 15 different values to describe a specific type of ICMP message. Some ICMP messages also use the values of the Code fields to further describe the different conditions. The checksum field covers the entire ICMP packet, and the algorithm is the same as the IP header checksum.

inspection and: used to test the entire ICMP packet. However, the IP header checks and does not verify the contents of the IP datagram, so there is no guarantee that the transmitted ICMP message will not cause errors.

ICMP message classification

ICMP messages fall into two categories: one is the error message that informs the cause of the error (error messages), and the other is the query message for the diagnostic (query packet)

Common ICMP message types

The different types are determined collectively by the Type fields and Code fields in the message.

Here are a few common ICMP messages:

1

Our daily use of the most ping, is the response request (TYPE=8) and Answer (TYPE=0), a host sends a TYPE=8 ICMP message to a node, if there is no exception on the way (for example, dropped by the router, the target does not respond to ICMP or transmission failure), the target returns the Type The =0 ICMP message indicates that this host is present and more detailed tracert the network distance between the host and the target by calculating the node through which the ICMP packets are passed.

2. Destination Unreachable, source suppression, and super-times text



3. Timestamp

Icmp:internet Control Message Protocol