I am connected to a Telnet server with Putty and looking at what is going on on the connection using Wireshark. The Telnet server rejects any Telnet options, so this is a pure NVT.
When I press Ctrl+D in Putty, it sends the following command to the Telnet server:
0xff 0xec
or, in decimal,
255 236
This looks a lot like a two-byte Telnet command, with the first byte (255) being IAC. However, while looking at RFC 854, I cannot find any mention of a command number 236 (0xec = 236, not to be confused with the Character Erase (EC) command).
Does anybody knows what this is? Am I missing something in the RFC or is this command defined somewhere else?
According to this, it is an End of File command.
The value is defined in RFC1116, which was in turn obsoleted by RFC1184, which defines the same EOF value.