Options give the client and server a common view of the connection. They can be
negotiated at any time during the connection by the use of commands. They are
described in separate RFCs.
The following are examples of common options:
Decimal code
Name
RFC
3
suppress go ahead
858
5
status
859
1
echo
857
6
timing mark
860
24
terminal type
1091
31
window size
1073
32
terminal speed
1079
33
remote flow control
1372
34
linemode
1184
36
environment variables
1408
Either end of a Telnet conversation can locally or remotely enable or disable an
option. The initiator sends a 3-byte command of the form:
IAC
Type of Operation
Option
The response is of the same form. Operation is one of:
Description
Decimal Code
Action
WILL
251
Sender wants to do something.
DO
252
Sender wants the other end to do something.
WONT
253
Sender does not want to do something.
DONT
254
Sender wants the other not to do something.
Associated with each of the these commands are various possible responses:
Sender Sent
Receiver Responds
Implication
WILL DO
The sender would like to use a certain facility if the receiver can
handle it.
Option is now in effect.
WILL DONT
Receiver says it cannot support the option.
Option is not in effect.
DO WILL
The sender says it can handle traffic from the sender if the sender
wishes to use a certain option.
