Basic Structure and packet type of ICMP protocol (1)

In network protocols, ICMP has many functions. It can contribute to network security, report data errors, and perform fault isolation and recovery. Let's take a closer look at this person-to-man agreement.

ICMP protocol Introduction

ICMP stands for Internet Control Message Protocol. The Chinese name is Internet Control Message Protocol. It works at the OSI network layer and reports errors to source hosts in data communication. ICMP supports fault isolation and recovery.

The network itself is unreliable. during network transmission, many emergencies may occur and data transmission may fail. The IP protocol at the network layer is a connectionless protocol that does not handle faults in network layer transmission. The ICMP protocol at the network layer makes up for the IP address shortage. It uses the IP protocol for information transmission, provide Error information feedback at the network layer to the source node in the data packet. The ICMP header is 8 bytes long, as shown in structure 1.

 

Figure 1 ICMP header structure)

Type: identifies the generated error message. It is the first field in the ICMP message;

Code: further limit the generation of ICMP packets. This field is used to find the cause of the error;

Checksum: The Checksum value used by ICMP is stored;

Unused: reserved field for future use. The starting value is set to 0;

Data: contains the IP header of all received data packets. It also contains the first eight bytes of data in the IP datagram;

The diagnostic packet types provided by ICMP are shown in table 1.