TELNET Negotiation Sequence Options on PuTTY

With the default settings of PuTTY (at least as of v0.73 released: 29-Sep-19) as a TELNET client, it sends the following characters as a part of its negotiation sequence options to the connected server.

..... .....'.........

Following are the actual Hex characters: ff fb 1f ff fb 20 ff fb 18 ff fb 27 ff fd 01 ff fb 03 ff fd 03

Decimal: 255 251 31 255 251 32 255 251 24 255 251 39 255 253 1 255 251 3 255 253 3

Here is an incomplete list of descriptions for these options:

Binary ValueTokenDescription1SEND503USERVARNEW-ENVIRON command24TTYPETerminal type option31NAWSWindow size option32N/AN/A39NEW-ENVIRONEnvironment variables251WILLConfirm willingness to negotiate253DOIndicate willingness to negotiate255IACMarks the start of a negotiation sequence

To disallow PuTTY to send these options, navigate to Connection -> Telnet and switch the Telnet Negotiation Mode: to Passive

Whether or not these negotiation sequences are important is a relative question based on the needs & behaviour of the server to handle these options. These options are different for different clients. It’s always best to use the client that the manufacturer recommends as they probably have already used the same client to test their telnet server.

PuTTY Negotiation Sequence Options [Sheet] More about Telnet Negotiation Options

#14, #apostrophe, #error, #login, #login-error, #putty, #telnet

#Apostrophe #Error #Telnet #PuTTY #Login #LoginError