Request for Comments: 862
This RFC specifies a standard for the ARPA Internet community. Hosts on the ARPA Internet that choose to implement an Echo Protocol are expected to adopt and implement this standard.
A very useful debugging and measurement tool is an echo service. An echo service simply sends back to the originating source any data it receives.
TCP Based Echo Service
One echo service is defined as a connection based application on TCP. A server listens for TCP connections on TCP port 7. Once a connection is established any data received is sent back. This continues until the calling user terminates the connection.
UDP Based Echo Service
Another echo service is defined as a datagram based application on UDP. A server listens for UDP datagrams on UDP port 7. When a datagram is received, the data from it is sent back in an answering datagram.