ICMP Protocol Internet Control Message Protocol

The ICMP Protocol Internet Control Message Protocol ICMP (Internet Control Message Protocol) is a Protocol between the network layer and the transport layer. Its main function is to transmit network diagnostic information. ICMP transmission information can be divided into two types: error information, which can be used to diagnose network faults. We already know that the IP protocol works in the "Best Effort" way. If the IP package is not transmitted to the destination, or an error occurs in the IP package, the IP protocol itself will not make any further efforts. However, the host and the router that sends the upstream IP packet do not know the downstream has errors and faults, and they may continue to send the IP packet. Through the ICMP packet, the downstream routers and hosts can report error messages to the upstream, so that the upstream routers and hosts can be adjusted. It should be noted that ICMP only provides specific types of error reporting, which cannot help the IP protocol become a reliable protocol. Another type of information is information of the nature of the consulting (Informational). For example, if a computer asks who is on each vro in the path, then each vro uses an ICMP packet to answer the question. (ICMP is based on the IP protocol. That is to say, an ICMP packet needs to be encapsulated in an IP packet and then transmitted over the Internet. ICMP is an essential part of an IP set. That is to say, any computer that supports the IP protocol must simultaneously implement ICMP .) ICMP packet structure: A bunch of Types ICMP packet has three parts: Type, Code, and Checksum. Type indicates a large Type of ICMP packet, and Code is a small Type subdivided within a Type. Different Types and codes are available for different error messages or consultation information. As we can see from the above, ICMP supports many types, just like Swiss Army knife, and has various functions. The Checksum is similar to the header checksum of the IP protocol, but it is different from the checksum in the IP protocol. Here, the Checksum verifies the entire ICMP packet (including the header and data ). The formats of the remaining ICMP packets vary according to different types. On the other hand, an ICMP packet is usually triggered by an IP packet. The header and part of the trigger IP packet will be contained in the Data Part Of The ICMP packet. ICMP protocol is the basis for implementing ping and traceroute commands. These two tools are commonly used for network troubleshooting.