Unwanted Telnet protocol bytes

When connecting to a PortServer II port through a socket from our application, we occasionally see the byte sequence: FF FD 03 FF FB 03 FF FB 01

I believe this is related to telnet. We do not want telnet (or whatever it is that injects these data bytes) enabled on the port. How do we disable it?


Try connecting to the raw socket as opposed to the telnet socket. Telnet base socket starts at 2000 and raw starts at 2100. For say port 1:
2001 = Telnet port 1
2101 = Raw port 1

When issuing a ‘set ports’ command, does it apply to both ranges 2xxx and 21xx or will I need to configure the 21xx ports as I have configured the 2xxx ports?


“set ports” applies to the serial port of the Portserver II itself, whereas accessing TCP port 2001 (ascii) or 2101 (raw) are two different ways of connecting to that port. Therefore the “set ports” command applies to both TCP socket representations for that port.

Great - Thanks.

Does the PortServer close the 2xxx ports if there is no telnet client response? I seem to be losing the socket connection after some time. I don’t see a configuration option related to inactivity timeout, so I’m wondering if the PortServer closes the port for another reason related to telnet.

I believe the following knowledge base article may be helpful:


Maybe that’s it. Can the tcp keep alive be disabled?

No, it can not be disabled, it can only be set to a high value.