Shulou(Shulou.com)06/01 Report--

The so-called ICMP protocol, the full name is Internet Control Message Protocol, the Chinese meaning Internet control message protocol.

It is a subprotocol of the TCP/IP protocol family, which is used to transfer control messages between IP hosts and routers.

The control message refers to the message of the network itself, such as whether the network is unreachable, whether the host is reachable, whether the route is available, and so on.

Although these control messages do not transmit user data, they play an important role in the transmission of user data.

The role of ICMP

ICMP protocol is of great significance for network security.

The characteristics of the ICMP protocol determine that it is very easy to be used in routers and hosts on the network.

For example, you can use the ICMP packet size specified by the operating system not to exceed 64KB to initiate a "Ping of Death" to the host.

(Ping of death) *. The principle of "Ping of Death" * * is that if the size of the ICMP packet exceeds the 64KB upper limit

A memory allocation error occurs on the host, causing the TCP/IP stack to crash and causing the host to panic. In addition, ICMP packets are sent to the target host for a long time, continuously and in large quantities

And eventually paralyze the system.

A large number of ICMP packets will form a "ICMP storm", which makes the target host consume a lot of CPU resources and run.

The CMP package has an 8-byte header in which the first four bytes are in a fixed format, including an 8-bit type field, an 8-bit code field, and a 16-bit checksum

The last 4 bytes vary according to the type of ICMP packet.

ICMP provides consistent and understandable error reporting information. The error message sent is returned to the device that sent the original data, because only the sending device is the logical receiver of the error message.

The sending device can then determine the type of error based on the ICMP message and determine how to better resend the failed packet.

But the only function of ICMP is to report problems rather than correct errors, and the task of correcting errors is done by the sender.

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