|Internet protocol suite|
A host may connect to a server that supports the Echo Protocol using the Transmission Control Protocol (TCP) or the User Datagram Protocol (UDP) on the well-known port number 7. The server sends back an identical copy of the data it received.
On UNIX-like operating systems an echo server is built into the inetd daemon. The echo service is usually not enabled by default. It may be enabled by adding the following lines to the file /etc/inetd.conf and telling inetd to reload its configuration:
echo stream tcp nowait root internal echo dgram udp wait root internal