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-   -   Telnet login: Notification format (http://www.linuxquestions.org/questions/linux-networking-3/telnet-login-notification-format-343408/)

55riaz 07-15-2005 07:40 AM

Telnet login: Notification format
 
When a client try to connect with telnet server they negogiate some options in a standard formats define in various RFCs (854,856 etc). example of formats are

COMMAND FROM Server >> IAC DO TType
COMMAND FROM Client >> IAC WILL TType
COMMAND FROM Server >> IAC DO NAWS
COMMAND FROM Client >> IAC WONT TSpeed
COMMAND FROM Client >> IAC WONT XDLoc
COMMAND FROM Client >> IAC WILL NEnvOp
COMMAND FROM Client >> IAC SB NAWS 0 80 0 25 IAC SE
...


Can any one tell me when client successfully login to the server what sort of standard notification will be send by the server to the client. I am asking this question because i found different responses from windows telnet server and linux telnet server. I donot find that information in any RFC.

rjlee 07-15-2005 06:59 PM

Re: Telnet login: Notification format
 
Quote:

Originally posted by 55riaz
Can any one tell me when client successfully login to the server what sort of standard notification will be send by the server to the client. I am asking this question because i found different responses from windows telnet server and linux telnet server. I donot find that information in any RFC.
Each option can be found described in its own RFC. The TELNET protocol itself is described in STD008 (http://www.rfc-editor.org/cgi-bin/rf...ile_format=txt), a collection of RFCs including RFC854 (TELNET protocol) and RFC855 (TELNET option format). I suspect that these have probably been superceeded by other documents as well.

According to the standard, the server is not required to send any requests. But if it wants to use any feature that isn't part of the basic raw data transfer of TELNET, then it must first negotiate the option by exchanging a WILL and DO token for the option. (This is an exchange, because the tokens can come in either order and neither is necessarily a reply).

In general, servers will send requests based on the options supported by the server and on the facilities supported by the network terminal that the server emulates. This will usually mean at least one authentication option (since TELNET authentication is fundamentally insecure).

Normally, TELNET options are requested from the client side. NAWS is a protocol to ask one side to change its terminal size to match the size of the terminal on the other side, instead of using a default 80x23 (I think) terminal. This is often requested by client connections.

There are several options that haven't made it into RFCs yet. I like MCCP (MUD Client Compression Protocol), which compresses data-streams.

So basically, there is no single standard set of options that the either terminal sends. But either terminal can send any option at any time.

Does that help you any?

55riaz 07-28-2005 02:06 AM

Sorry for delayed response, actullay i was out of town. First of all thanks for such comprehensive reply. Actually i am thinking to develop a generic tool which is responsible for providing security to any type of telnet servers. Thats why for interoperability i am looking for standards.


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