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Telnet Sequence Negotiation

Michael Griffin

5/28/2015 8:18:00 AM


> I'm thinking in particular after having said "IAC WILL <FOO>", and
> receiving a "IAC DO <FOO>", can I later sao "IAC WONT <FOO>" to stop
> FOOing? And when I do that, will I receive an acknowledgement?
>
> Another way to ask this is:
> If I received a "IAC DO <FOO>" after a "IAC WILL <FOO>", the other side
> has the ability to change its mind "IAC DON'T <FOO>". When they do
> that, should I reply with "IAC WON'T <FOO>", or just silently accept the
> new state of affairs?
>
> I think I realized the answer: If I receive a command that changes my
> state, then I should acknowledge with the new state. Defensive
> programming says I shouldn't expect an acknowledgement, but handle one
> cleanly.
>
> If I disable an option changes my handling of the data stream, I
> shouldn't disable the processing until the byte after the response of
> IAC DON'T/WON'T.
>

Lets see if this reply will post this time :)

https://support.microsoft.com/en-us... even through it's
Microsoft, it has a very good layout of the negotiation sequences.

Scroll down to the middle of the page where the heading is:

Associated with each of the these commands are various possible responses:

Basically if you send a DO or DON'T and get a reply, then you should
change the settings according to the response.

But you want to track responses sent, vs responses received. you don't
want an endless loop of you -> Them -> you -> them again.

If you send a query, get a response for that item, then cut it there.
If you receive query, reply back, then cut it there.

Mike
telnet://htc.zapto.org
3 Answers

Daniel Pitts

5/29/2015 4:30:00 AM

0

On 5/28/15 1:18 AM, Michael Griffin wrote:
>
> > I'm thinking in particular after having said "IAC WILL <FOO>", and
> > receiving a "IAC DO <FOO>", can I later sao "IAC WONT <FOO>" to stop
> > FOOing? And when I do that, will I receive an acknowledgement?
> >
> > Another way to ask this is:
> > If I received a "IAC DO <FOO>" after a "IAC WILL <FOO>", the other side
> > has the ability to change its mind "IAC DON'T <FOO>". When they do
> > that, should I reply with "IAC WON'T <FOO>", or just silently accept the
> > new state of affairs?
> >
> > I think I realized the answer: If I receive a command that changes my
> > state, then I should acknowledge with the new state. Defensive
> > programming says I shouldn't expect an acknowledgement, but handle one
> > cleanly.
> >
> > If I disable an option changes my handling of the data stream, I
> > shouldn't disable the processing until the byte after the response of
> > IAC DON'T/WON'T.
> >
>
> Lets see if this reply will post this time :)
>
> https://support.microsoft.com/en-us... even through it's
> Microsoft, it has a very good layout of the negotiation sequences.
>
> Scroll down to the middle of the page where the heading is:
>
> Associated with each of the these commands are various possible responses:
>
> Basically if you send a DO or DON'T and get a reply, then you should
> change the settings according to the response.
>
> But you want to track responses sent, vs responses received. you don't
> want an endless loop of you -> Them -> you -> them again.
>
> If you send a query, get a response for that item, then cut it there.
> If you receive query, reply back, then cut it there.
>

Yep, that's basically what I wrote. Only and always send a message if
you are trying to make the state change, or are acknowledging a state
change.

Michael Griffin

5/29/2015 4:35:00 AM

0

On 5/28/2015 11:30 PM, Daniel Pitts wrote:
>>
>> Lets see if this reply will post this time :)
>>
>> https://support.microsoft.com/en-us... even through it's
>> Microsoft, it has a very good layout of the negotiation sequences.
>>
>> Scroll down to the middle of the page where the heading is:
>>
>> Associated with each of the these commands are various possible
>> responses:
>>
>> Basically if you send a DO or DON'T and get a reply, then you should
>> change the settings according to the response.
>>
>> But you want to track responses sent, vs responses received. you don't
>> want an endless loop of you -> Them -> you -> them again.
>>
>> If you send a query, get a response for that item, then cut it there.
>> If you receive query, reply back, then cut it there.
>>
>
> Yep, that's basically what I wrote. Only and always send a message if
> you are trying to make the state change, or are acknowledging a state
> change.
>

Perfect, then you should be all set.

Michael Griffin

5/29/2015 4:36:00 AM

0

On 5/28/2015 11:30 PM, Daniel Pitts wrote:

>> Lets see if this reply will post this time :)
>>
>> https://support.microsoft.com/en-us... even through it's
>> Microsoft, it has a very good layout of the negotiation sequences.
>>
>> Scroll down to the middle of the page where the heading is:
>>
>> Associated with each of the these commands are various possible
>> responses:
>>
>> Basically if you send a DO or DON'T and get a reply, then you should
>> change the settings according to the response.
>>
>> But you want to track responses sent, vs responses received. you don't
>> want an endless loop of you -> Them -> you -> them again.
>>
>> If you send a query, get a response for that item, then cut it there.
>> If you receive query, reply back, then cut it there.
>>
>
> Yep, that's basically what I wrote. Only and always send a message if
> you are trying to make the state change, or are acknowledging a state
> change.
>

Perfect, then you should be all set.