Telnet Options

  • Article

Clients and servers can negotiate additional options, beyond the default functionality provided by NVT. The telnet options are described in a number of extensions to the Telnet RFC, and RFC 855 describes the mechanism for specifying telnet options. Each telnet option is assigned a number.

Options are usually negotiated at the beginning of a Telnet session, but can also be requested during the session. Options are negotiated by exchanging option code sequences. One partner can request an option; the other can agree to the request or not. The negotiation syntax involves the use of four protocol verbs: WILL and DO, to request or offer to provide an option, and WON'T and DON'T, to do the opposite. The negotiation of options can potentially result in a nonterminating loop of acknowledgments.

Services for UNIX supports the following telnet options:

  • NTLM authentication, which uses a randomization algorithm and an encrypted password to authenticate users.

  • Terminal emulation, in which a program allows a computer to act like a specified terminal. Supported terminal types include VTNT, VT100, VT52, and ANSI.