要求Telnet服务器忽略命令

Question

Let's say I have a working Telnet server and client; the client is my own C-programmed creation, though the server is not under my control (in my case, it is a Perle Systems IOLAN SCS48, but it could be any RFC2217-enabled Telnet device).

I want to use the devices serial tunneling features (via the RFC 2217 protocol for Telnet), but only at the start of the connection. As such, I receive four negotiation requests from the server ( WILL TRANSMIT-BINARY , DO TRANSMIT-BINARY , WILL ECHO , DO SUPPRESS-GO-AHEAD , WILL SUPPRESS-GO-AHEAD and DO COM-PORT-OPTION ; the last one being from RFC 2217), to all of which I respond, and then set baudrate, datasize, parity bit and stop bit.

So far so good, but now I want to re-arrange the communication so the server ignores all future commands (especiall the IAC character 0x255 ), so I can pass Hex-converted strings through the device to the receiving end (connected to the device's serial port), which gets every single byte I send (and not lose three bytes for every 0x255 that is somewhere in my string, or seven bytes where there is 0x255 0x250 ( IAC SB )).

Alternatively, would there be a possibility to make the server pass an escaped escape char (two 0x255's in a row, which are then printed as-input) as a single 0x255?

I do not want to close the connection to reopen it is a raw one, as my serial settings would be lost (because that's how the device's COM port redirection works, I suppose). However, I do not need to re-establish command listening, so the connection can simply be closed and reopened as another Telnet connection if I need to reconfigure the baudrate.

How would I approach this?

Answer 1

If there's a standard IAC DO IGNORE-FURTHER-IACS, I've never heard of it.

RFC 854 does not explain this very well, but the documented meaning of two IACs in a row is "data byte 255", so I think the server is already supposed to pass 0x255 0x255 onward as a single 0x255. Is it not doing that?