tailieunhanh - Internet Control Message Protocol (ICMP)

TCP and UDP exist primarily to deliver upper-layer data across a network. Whether connection oriented or connectionless, fundamentally the process of delivering the data is the same | Internet Control Message Protocol ICMP TCP and UDP exist primarily to deliver upper-layer data across a network. Whether connection oriented or connectionless fundamentally the process of delivering the data is the same identify the source and destination application ports format the data accordingly and deliver the data to IP. This process works well when the network is functioning without error and when systems are operating correctly and know how to deliver data through routers and subnets to any destination anywhere. The problem is that the network does not always work routes fail and data may not be able to be delivered or it may need to be directed elsewhere to be successfully delivered . To facilitate this process the ICMP protocol was developed. In many ways ICMP functions like the traffic cop and policeman of the network. Because IP and UDP lack any mechanism for identifying that failures may occur on the network they need an external protocol that can provide information about routing failures and to report about delivery errors congestion delays and other conditions on the network. Indeed like the traffic cop notifying motorists about congestion delays or blocked intersections routers on the street ICMP provides a means to control the flow of traffic in an effort to ensure that the data can be reliably delivered. An important distinction to understand about ICMP is that it is an error-reporting mechanism not an error-correcting mechanism. That means that although ICMP can notify hosts of error conditions ICMP natively has no means or method of actually doing anything about the error condition. Instead ICMP relies on other protocols such as routing protocols or reliable protocols such as TCP to account for and address the particular error condition. The most well-known use of ICMP is through the use of the ping application. Ping is a network troubleshooting application that makes use of ICMP echo request and echo reply detailed in the next section .