TCP/IP basic ICMP protocol (1)

In the entire TCP/IP protocol family, ICMP is a negligible protocol for "users. The prerequisite for the previous agreement to make full use of its work is: "if everything is okay ".
However, in today's complex network environment, the aforementioned conditions may not be guaranteed: the configuration may be incorrect, the line may be disconnected, the device may be down, the router may be overloaded ,.... and so on. Therefore, we must have a mechanism to detect or notify various possible situations, which is the purpose of the ICMP protocol.
ICMP is most likely to be ignored because, in most cases, ICMP is only used for reference by the underlying network devices and is resolved. I'm afraid there are not many tools that really need to be executed by a labor-consuming user. The most representative tools are ping and traceroute. Let's unveil the secret of ICMP together...
ICMP protocol content
The full name of ICMP is Internet Control Message Protocol. From the technical perspective, ICMP is a "error detection and return mechanism", which enables us to detect the connection status of the network and ensure the accuracy of the connection. Its main functions include ﹕
· Detect whether a remote host exists.
· Establish and maintain route data.
· Re-import the data transfer path.
· Data traffic control.
ICMP allows machines to identify different connection conditions through different types and codes. Common categories are listed in the following table ﹕

ICMP is a very useful protocol, especially when we need to judge the network connection status. Next let's take a look at the commonly used ICMP instances to better understand the functions and functions of ICMP.
PING
Many people have used this command. It is the simplest tool to test whether two hosts can be connected smoothly ﹕