Document directory
- Significance of ICMP
- Message Type
- Error Report
- Query
The meaning of the existence of icmp ip provides unreliable connectionless datagram transmission. In this way, the IP protocol is designed to effectively use resources and provide a service that is best transmitted, it transmits a datagram from its original source end to the final destination end. However, it has two disadvantages: lack of Error Control and lack of auxiliary mechanisms. The IP protocol has no error reporting and error correction mechanisms. If an error occurs, what will happen? What happens if no router can reach the destination? The IP protocol also lacks a host and Management query mechanism. The host sometimes needs to determine whether a vro or another host is active, and sometimes the network administrator needs to obtain information from one host or vro. Internet Control Message Protocol (ICMP) is designed to make up for the above shortcomings. It is used with the IP Protocol (ICMP packets are transmitted as IP data ). ICMP messages are classified into two categories: Error-Reporting Message and query message ). Error Report messages report problems that may occur when processing an IP address data report to the router or host. Query Packets appear in pairs. This helps the host or network administrator obtain specific information from a vro or a host. The error report ICMP cannot correct the error. It only reports the error. The error correction is left to the high-level protocol, and the error message is always sent to the original source end. There are five types of errors that can be handled: ICMP error messages have the following key points: 1. ICMP error messages are no longer generated for the datagram containing ICMP error messages. 2. For segmented data packets, if not the first segment, no ICMP error message is generated. 3. For multicast address data packets, no ICMP error messages are generated. 4. Special addresses, such as 127.0.0.0 or 0.0.0.0, do not generate ICMP error packets. The destination cannot be tested. When the router cannot find a route for the datagram or the host cannot transmit the data report, the datagram is discarded, the router or host then sends the Destination Unreachable message back ). Source suppression of IP protocol is a connectionless protocol. The source host never knows whether some routers or target hosts have been overloaded by too many data packets, the source host never knows whether the datagram is generated too quickly, so that the router cannot forward or the target host cannot process it. If the receiving rate of the datagram is much faster than the forwarding rate, the cache of the receiver will overflow. At this time, the router or host has no choice but to discard the datagram. Source-quench message is designed to add traffic control to IP addresses. When the router or host discards the data report due to congestion, it wants the sender of the datagram to send the source suppression message. Time-exceeded message is generated in two cases. 1. Each datagram has a survival time field. During routing, the value of this field is reduced by 1 for each hop router. If this field is set to 0, the datagram is discarded, in this case, the router sends a time-out message to the source end. Second, when all the segments that constitute a packet fail to reach the host within a certain time limit, a time-out packet will also be generated. Parameter problems when a datagram is transmitted over the Internet, any ambiguity in a header may cause serious problems. If the vro or target host finds that a field in the datagram lacks a value, it discards the datagram and sends the parameter-problem message to the source end. Redirection sends a redirection packet in the following circumstances. If host a wants host B to send a datagram, vror2 R2 is obviously the most effective route option, but host a does not select R2, but R2 is selected. The datagram is sent to R1, when R1 finds the route table, it finds that the Group should go through R2. It sends the group to R2 and sends a redirection packet to host a at the same time. Then, the route table of host a is updated. There are four types of Query Packets: the echo-Request Message and the echo-reply message. They are combined to determine that the two systems can communicate with each other. The ping command creates a series of send and receive requests or send reply packets. Timestamp requests and answers can be sent to two systems (host or router) using timestamp request messages) and the timestamp Response Message to determine the time required for the IP datagram to return between two systems. It can also be used for clock synchronization between two machines. The Address Mask Request and response can obtain the mask of the target host. The router requests and answers the host's router request and answer to obtain whether the router in the local area network works normally.
