Icmp:internet Control Message Protocol

Icmp:internet Control Message Protocol.

is part of the IP layer , passing error messages or other information.
ICMP packets are encapsulated inside the IP datagram:
Detailed formats such as the following are seen:

Field meanings such as the following:

• 8-bit type. Indicates the meaning of the ICMP message. If the purpose is unreachable, time-out, request echo, etc.
• 8 is the code.

  A further description of the ICMP message is described. the type of ICMP message is determined by the Type field and the Code field together .

• 16-bit inspection and. and the IP header check and the algorithm same.

The ping program we use often is the transmission based on ICMP packets. PingClient sends an ICMP echo request message, and the server returns an ICMP echo reply message as a response after receiving the message. Both client and server send and receive the message at the kernel level, rather than through the user process.

echo Request and ECHO response message formats such as the following:

Type 0 + code 0 = Echo Reply type 8 + code 0 = Echo Request
There are several extra fields for the ICMP echo request and echo Reply message:

• Identifier. Represents the ID number of the sending process.
• Serial number.

  Starting from 0, add 1 for each new echo request that is sent.

• Option data. Actual load, such as Save send time. The receiving end calculates the round trip time by subtracting the send time from the current time.

The following are the results of the grab package:

The client sent a total of 4 echo requests to the server. The TTL field is in the IP header. Because ICMP belongs to the IP layer protocol, and the IP layer is unreliable, disconnected, best-effort transmission, ping occasionally occurs in the case of transmission errors.
Reference: "The specific interpretation of TCP/IP" 6th Chapter, 7th Chapter.

Icmp:internet Control Message Protocol