#Icmp checksum code#

Code: It is an 8-bit field that defines the subtype of the ICMP message.The values range from 0 to 127 are defined for ICMPv6, and the values from 128 to 255 are the informational messages. The ICMP message contains the following fields:

#Icmp checksum code#

The type defines the type of message while the code defines the subtype of the message. If the message is of error type, the error message contains the type and the code. The message format has two things one is a category that tells us which type of message it is. For example, suppose there are a client and a server, and the client wants to know whether the server is live or not, then it sends the ICMP message to the server. The query messages are those messages that help the host to get the specific information of another host. The error-reporting message means that the router encounters a problem when it processes an IP packet then it reports a message. The ICMP messages are usually divided into two categories: The ICMP resides in the IP layer, as shown in the below diagram.

If someone in-between reports the error, then the sender will resend the message very quickly. If no one reports the error, then the sender might think that the message has reached the destination. For example, if someone sends the message to the destination, the message is somehow stolen between the sender and the destination. The IP protocol does not have any error-reporting or error-correcting mechanism, so it uses a message to convey the information. In this case, the router sends the message to the sender that I could not send the message to that destination. As different types of errors can exist in the network layer, so ICMP can be used to report these errors and to debug those errors.įor example, some sender wants to send the message to some destination, but the router couldn't send the message to the destination. It is used for error handling in the network layer, and it is primarily used on network devices such as routers. The ICMP stands for Internet Control Message Protocol.