How are options negotiated in TELNET?
The correct answer and explanation is :
In TELNET, options are negotiated using a process called “option negotiation.” This negotiation allows the client and server to agree on various features or capabilities before the actual communication begins. The negotiation process in TELNET is based on a set of commands and responses that are sent between the client and server to decide which options will be used during the session.
TELNET Option Negotiation Process:
- Option Request:
The negotiation process begins when either the client or the server sends a request to enable or disable specific options. These requests are represented by control characters (bytes with values in the 240-255 range) that initiate negotiation. - IAC (Interpret As Command):
TELNET commands are distinguished by the IAC byte (0xFF), which indicates that the following byte or sequence of bytes is not data but a command. IAC is used to frame the negotiation commands, such as option requests and responses. For example, an IAC followed by a specific byte could indicate that the client wants to enable or disable a certain feature. - Negotiation Commands:
There are several TELNET commands used for negotiation:
- WILL: Indicates that the sender is willing to perform a certain option.
- WON’T: Indicates that the sender does not want to perform a certain option.
- DO: Requests that the other party enable the specified option.
- DON’T: Requests that the other party disable the specified option.
- SE (Subnegotiation End): Marks the end of a subnegotiation sequence.
- Response to Requests:
Upon receiving an option request (e.g., DO or WILL), the receiving party must respond with either a WILL or WON’T (if the sender requested the option to be enabled or disabled), or DO or DON’T (if the sender asked the recipient to enable or disable the option). If the option is agreed upon, it is enabled and used throughout the session. - Default Behavior:
If no option negotiation occurs, the default behavior of the TELNET session is used. This means that certain capabilities, such as terminal type or echoing, may not be actively negotiated and may follow standard defaults.
This process ensures that both ends of the connection are synchronized on what capabilities will be used during the TELNET session. Option negotiation allows TELNET to be flexible and adaptable to various terminal types and communication preferences.