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RFC 862 INTERNET STANDARD APPLICATIONS · DIAGNOSTICS · ECHO

Echo Protocol

A tiny service that sends back whatever it receives, used as a debugging and measurement tool.

On rfc-editor.org ↗
PUBLISHED
May 1983
AUTHORS
J. Postel
STREAM
Legacy
TCP PORT
7
UDP PORT
7
DOI
10.17487/RFC0862

RFC text

Original text · RFC Editor View on rfc-editor.org ↗ 
Network Working Group                                          J. Postel
Request for Comments: 862                                            ISI
                                                                May 1983



                             Echo Protocol




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.

AI ELI5

On this page
PROBLEMOperators need a very simple way to debug and measure a network path.
MECHANISMAn echo service sends back to the originating source any data it receives, on port 7 over either TCP or UDP.
STATUS TODAYHosts that choose to implement an Echo Protocol are expected to follow this standard.

§1What an Echo Service Is

The RFC calls an echo service a very useful debugging and measurement tool. It simply sends back to the originating source any data it receives. Hosts that choose to implement an Echo Protocol are expected to adopt this standard; implementing it is optional.

Send it anything and it hands the same thing back, which shows the connection works.

§2TCP and UDP Echo

The TCP-based service is connection based. A server listens for TCP connections on port 7. Once a connection is established, any data received is sent back, and this continues until the calling user terminates the connection.

The UDP-based service is datagram based. A server listens for UDP datagrams on port 7. When a datagram is received, its data is sent back in an answering datagram.

On a phone call (TCP) it repeats everything until you hang up. By postcard (UDP) it mails back each postcard's message.

§3Standard Status

RFC 862 is an Internet Standard from May 1983. The text is short and defines only the two port 7 behaviors above; it sets no message format, limits or security rules.

It is a very small rulebook with only two rules: listen on number 7 and send back what you hear.