Re: [tcpm] SYN/ACK Payloads, draft 01

"Adam Langley" <> Mon, 11 August 2008 23:17 UTC

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Date: Mon, 11 Aug 2008 16:17:08 -0700
From: Adam Langley <>
To: Sergio Freire <>
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Subject: Re: [tcpm] SYN/ACK Payloads, draft 01
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On Mon, Aug 11, 2008 at 3:03 PM, Sergio Freire <> wrote:
> Meanwhile, if you can take a look at our work, it would be great for further
> discussion (regarding the way of extending tcp options and not the name
> service itself).

Somehow I've already read your paper, although don't have any idea
where I got the pointer from!

A few questions:

There's no legacy mode for active opens because the port name mode is
singled with a destination port number of 0, right?

You're taking the option number 0x45 for your length indicator. Lars
pointed out to me a few months ago that 254 and 255 are assigned for
this if you're using it over real networks.

Assuming that a SYN frame is sent to port 0, requesting a named TCP
service which the destination knows about: what's the source port
number of the resulting SYN/ACK? I think I'm reading that it's chosen

>From the table in 3.3 it doesn't appear that there's any SYNACK
payload, is that correct?

It's unfortunate that there's no way for clients to gradually start
using such a scheme, but you can't extend the option space in SYNs
and, if you used non-0 destination ports, some hosts may enqueue the

In short, if my understanding is correct, I don't believe these two
schemes interfere, even on a single connection.

Are you intending on trying to get an option number assigned for this?



Adam Langley
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