3.2.3 Control Functions: RFC-854, pp. 7-8

The list of Telnet commands has been extended to include EOR (End-of-Record), with code 239 [TELNET:9].

Both User and Server Telnets MAY support the control functions EOR, EC, EL, and Break, and MUST support AO, AYT, DM, IP, NOP, SB, and SE.

A host MUST be able to receive and ignore any Telnet control functions that it does not support.

DISCUSSION:

Note that a Server Telnet is required to support the Telnet IP (Interrupt Process) function, even if the server host has an equivalent in-stream function (e.g., Control-C in many systems). The Telnet IP function may be stronger than an in-stream interrupt command, because of the out- of-band effect of TCP urgent data.

The EOR control function may be used to delimit the stream. An important application is data entry terminal support (see Section 3.3.2). There was concern that since EOR had not been defined in RFC-854, a host that was not prepared to correctly ignore unknown Telnet commands might crash if it received an EOR. To protect such hosts, the End-of-Record option [TELNET:9] was introduced; however, a properly implemented Telnet program will not require this protection.