Discard Protocol
A tiny service that silently throws away whatever it receives, used as a debugging and measurement tool.
Postel, J., "Discard Protocol", STD 21, RFC 863, DOI 10.17487/RFC0863, May 1983, <https://www.rfc-editor.org/info/rfc863>.
@misc{rfc863,
series = {Request for Comments},
number = 863,
howpublished = {RFC 863},
publisher = {RFC Editor},
doi = {10.17487/RFC0863},
url = {https://www.rfc-editor.org/info/rfc863},
author = {J. Postel},
title = {{Discard Protocol}},
pagetotal = 1,
year = 1983,
month = may,
} RFC text
Network Working Group J. Postel
Request for Comments: 863 ISI
May 1983
Discard Protocol
This RFC specifies a standard for the ARPA Internet community. Hosts on
the ARPA Internet that choose to implement a Discard Protocol are
expected to adopt and implement this standard.
A useful debugging and measurement tool is a discard service. A discard
service simply throws away any data it receives.
TCP Based Discard Service
One discard service is defined as a connection based application on
TCP. A server listens for TCP connections on TCP port 9. Once a
connection is established any data received is thrown away. No
response is sent. This continues until the calling user terminates
the connection.
UDP Based Discard Service
Another discard service is defined as a datagram based application on
UDP. A server listens for UDP datagrams on UDP port 9. When a
datagram is received, it is thrown away. No response is sent.
AI ELI5
On this page
§1What a Discard Service Is
The RFC calls a discard service a useful debugging and measurement tool. It simply throws away any data it receives. Hosts that choose to implement a Discard Protocol are expected to adopt this standard; implementing it is optional.
You send it stuff and it never sends anything back.
§2TCP and UDP Discard
The TCP-based service is connection based. A server listens for TCP connections on port 9. Once a connection is established, any data received is thrown away and no response is sent. This continues until the calling user terminates the connection.
The UDP-based service is datagram based. A server listens for UDP datagrams on port 9. When a datagram is received, it is thrown away and no response is sent.
Over a phone call it listens until you hang up and says nothing. For postcards it reads each one and drops it in the bin.
§3Standard Status
RFC 863 is an Internet Standard from May 1983. The text defines only the two port 9 behaviors above.
It is a listener that never answers: everything sent to it just disappears.