The Discard Protocol is a service in the

Internet Protocol Suite The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...

defined in RFC 863. It was designed for testing, debugging, measurement, and host-management purposes. A host may send data to a host that supports the Discard Protocol on either

Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly ...

(TCP) or

User Datagram Protocol In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) network. ...

(UDP)

port number In computer networking, a port is a number assigned to uniquely identify a connection endpoint and to direct data to a specific service. At the software level, within an operating system, a port is a logical construct that identifies a specific ...

9. The data sent to the server is simply discarded. No response is returned. For this reason, UDP is usually used, but TCP allows the services to be accessible on session-oriented connections (for example via

HTTP The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, ...

proxies or some

virtual private network A virtual private network (VPN) extends a private network across a public network and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. The be ...

(VPN)).

Inetd implementation

On most

Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...

operating systems a discard server is built into the

inetd inetd (internet service daemon) is a super-server daemon on many Unix systems that provides Internet services. For each configured service, it listens for requests from connecting clients. Requests are served by spawning a process which runs the ...

(or

xinetd In computer networking, xinetd (''Extended Internet Service Daemon'') is an open-source super-server daemon which runs on many Unix-like systems, and manages Internet-based connectivity. It offers a more secure alternative to the older inetd ( ...

)

daemon Daimon or Daemon (Ancient Greek: , "god", "godlike", "power", "fate") originally referred to a lesser deity or guiding spirit such as the daimons of ancient Greek religion and mythology and of later Hellenistic religion and philosophy. The word ...

. The discard service is usually not enabled by default. It may be enabled by adding the following lines to the file and reloading the configuration: discard stream tcp nowait root internal discard dgram udp wait root internal The Discard Protocol is the TCP/UDP equivalent of the Unix file-system node

/dev/null 




In some operating systems, the null device is a device file that discards all data written to it but reports that the write operation succeeded. This device is called /dev/null on Unix and Unix-like systems, NUL: (see TOPS-20) or NUL on CP/M an ...

. Such a service is guaranteed to receive what is sent to it and can be used for debugging code requiring a guaranteed reception TCP or UDP payloads. On various routers, this TCP or UDP port 9 for the Discard Protocol (or port 7 for the

Echo Protocol The Echo Protocol is a service in the Internet Protocol Suite defined in RFC 862. It was originally proposed for testing and measurement of round-trip times in IP networks. A host may connect to a server that supports the Echo Protocol using the ...

relaying ICMP datagrams) is also used by default as a proxy to relay Wake-on-LAN (WOL) magic packets from the Internet to hosts on the local network in order to wake them up remotely (these hosts must also have their network adapter configured to accept WOL datagrams and the router must have this proxy setting enabled, and possibly also a configuration of forwarding rules in its embedded

firewall Firewall may refer to: * Firewall (computing), a technological barrier designed to prevent unauthorized or unwanted communications between computer networks or hosts * Firewall (construction), a barrier inside a building, designed to limit the spre ...

to open these ports on the Internet side).

References

External links

RFC 348
the Discard Process
RFC 863
the Discard Protocol Application layer protocols {{Internet-stub

Inetd implementation

See also

References

External links