Subject: RE: [tcpm] UTO: SHOULD send option in first segment after the SYN?

From: Fernando Gont <[email-masked]>
Date: Sat, 07 Oct 2006 05:15:15 -0300

At 18:10 28/09/2006, Caitlin Bestler wrote:

> >   A host that supports the TCP User Timeout Option SHOULD include one
> >   in each packet that carries a SYN flag, but need not.  [MEDINA] has
> >   shown that unknown options are correctly handled by the vast
[....]

>Given that there is no need to pre-validate support for UTO, and that
>the suggestion UTO value may be ignored on a SYN, I think placing the
>initial UTO value on the first data carrying packet makes more sense.

Do you suggest to replace the "SHOULD include one in each packet that 
carries a SYN flag", or rather suggest to include an *additional* 
"SHOULD" for including the option in the first data segment?

Kindest regards,

--
Fernando Gont
e-mail: [email-masked] || [email-masked]
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From: Fernando Gont <[email-masked]>
Date: Sat, 07 Oct 2006 05:15:15 -0300

[....]

Kindest regards,

---

From: "Caitlin Bestler" <[email-masked]>
Date: Mon, 9 Oct 2006 08:59:26 -0700

Fernando Gont wrote:
>>>   A host that supports the TCP User Timeout Option SHOULD include
>>>   one in each packet that carries a SYN flag, but need not.
>>>   [MEDINA] has shown that unknown options are correctly handled by
>>> the vast [....] 
> 
> Do you suggest to replace the "SHOULD include one in each
> packet that carries a SYN flag", or rather suggest to include
> an *additional* "SHOULD" for including the option in the first data
> segment? 
> 
> Kindest regards,

Many SYN-Cookie or similar strategies are only activated
when the passive side suspects that it might be under attack.
Such systems might do initial allocations based on the SYN
alone. Therefore including the initial UTO on *both* the SYN
and the next segment makes sense. I can't think of any real
harm in sending both. Assuming that the connection is actually
going to be open long enough to have justified sending a UTO
the "wasted" bandwidth is miniscule.

---

From: Gorry Fairhurst <[email-masked]>
Date: Thu, 12 Oct 2006 11:15:35 +0100

Seems fine to me, sorry I didn't respond back to the last posting.

So this says, if a host thinks it may use UTO, then it would need to be 
included in the SYN. Some TCP implementations also "like" to know what 
options could be used at connection establishment, rather than 
introducing "random" options as the connection progresses. Including 
these in the SYN exchange simplifies processing of later segments and 
also provides an element of "protection" from spurious options being 
inserted that were not intended by the sender.

Gorry