The ICMP Echo and Echo Reply messages are sent and received by the ping command. In fact, when people say that they sent a ping packet, they really mean that they sent an ICMP Echo Request. These two messages are very much self-explanatory. The Echo Request simply means that the host to which it is addressed should reply to the packet. The Echo Reply is the ICMP message type that should be used in the reply. The Request includes some data, which can be specified by the ping command; whatever data is sent in the Echo Request is sent back in the Echo Reply.
Normally, an echo request often includes a set of data that you can specify using the ping command. When a host makes an echo reply, all the data in the ICMP echo request will be sent back.
The ping command provides the users with all the modalities of sending the ICMP echo requests and ICMP echo replies. Among the specifications that you may have to make are the source and the destination addresses. Besides, you will also need to set the other modalities in the IP Header section.
When to Use Echo Request and Echo Reply Messages
Notably, whenever the basic connectivity operations fail, one of the most basic tests that the users opt to perform is to verify if the remote system attached to their client machines is up and running. This is where the ICMP query messages come into play. These messages are vital tools for network testing and troubleshooting applications.
The user sends an ICMP Echo Request message to the remote destination system, with the system replying with an ICMP Echo Reply message to deliver the feedback. According to RFC 1122, each host must implement the ICMP Echo server, making this service mandatory.