Re: [tcpm] I-D Action: draft-nishida-tcpm-agg-syn-ext-00.txt

Hi, Yoshi,

> On Feb 2, 2021, at 11:12 PM, Yoshifumi Nishida <nsd.ietf@gmail.com> wrote:
> 
> Hi folks,
> 
> I prepared a draft for SYN option space extensions.
> I know this is a difficult issue in TCP and has been discussed for a long time. 
> But, I'm thinking that it might be a good time to discuss it again.

The proposal has two parts, which are (AFAICT) separable:
A. Aggregated options
B. Adding more option space in the 3rd packet of a 3WHS

(A) is fine, although the most significant issue is legacy interaction.

(B) is no longer extending the SYN; it’s actually just post-SYN activation of new options. 

> Key ideas of the draft are the followings.
> 1: drastic changes in TCP's spec will not be required 
>     (it does not require updating TCP header format nor using multiple SYN packets or additional SYN-like packets)

Post-SYN activation of new options is quite a drastic change. 

Nevermind the question of what happens to data in the SYN, which normally MUST be passed to the application at the receiver after the final ACK is received, but here MUST NOT. And the data that might go in the other direction in the 3rd message with the ACK.

Basically, you’re proposing to change the 3WHS to a 5WHS, which is a lot more significant and complex than described here (there are a lot of failure modes not addressed, for one).

> 2: utilize the option negotiation schemes in mptcp for generic purposes. so, I think it can be considered middlebox friendly.

MPTCP is negotiating variants of an option that is already active (AFAICT); that’s not the same as activating new options.

> 3: it has some limitations (e.g it can only extend around 30-40 bytes for SYN option space). But, if it's combined with EDO, we can use more option space.
>     (depends on how EDO draft will progress, though)

If you have EDO, then just negotiate it and activate options after the connection is established. But that’s not the problem at hand - the problem is activation of options in the SYN. AFAICT, this does not do that.

Joe

> 
> Please let me know if you have any questions or comments or suggestions.
> 
> Thank you so much!
> --
> Yoshi
>  
> 
> ---------- Forwarded message ---------
> From: <internet-drafts@ietf.org <mailto:internet-drafts@ietf.org>>
> Date: Tue, Feb 2, 2021 at 10:45 PM
> Subject: I-D Action: draft-nishida-tcpm-agg-syn-ext-00.txt
> To: <i-d-announce@ietf.org <mailto:i-d-announce@ietf.org>>
> 
> 
> 
> A New Internet-Draft is available from the on-line Internet-Drafts directories.
> 
> 
>         Title           : Aggregated Option for SYN Option Space Extension
>         Author          : Yoshifumi Nishida
>         Filename        : draft-nishida-tcpm-agg-syn-ext-00.txt
>         Pages           : 14
>         Date            : 2021-02-02
> 
> Abstract:
>    TCP option space is scarce resource as its max length is limited to
>    40 bytes.  This limitation becomes more significant in SYN segments
>    as all options used in a connection should be exchanged during SYN
>    negotiations.  This document proposes a new SYN option negotiation
>    scheme that provide a feature to compress TCP options in SYN segments
>    and provide more option space.  The proposed scheme does not update
>    the format of TCP header nor transmit any additional SYN or SYN-like
>    segments so that it has lower risks for middlebox interventions.  In
>    addition, by combining another proposal for option space extension,
>    it is possible to provide further option space.
> 
> 
> The IETF datatracker status page for this draft is:
> https://datatracker.ietf.org/doc/draft-nishida-tcpm-agg-syn-ext/ <https://datatracker.ietf.org/doc/draft-nishida-tcpm-agg-syn-ext/>
> 
> There are also htmlized versions available at:
> https://tools.ietf.org/html/draft-nishida-tcpm-agg-syn-ext-00 <https://tools.ietf.org/html/draft-nishida-tcpm-agg-syn-ext-00>
> https://datatracker.ietf.org/doc/html/draft-nishida-tcpm-agg-syn-ext-00 <https://datatracker.ietf.org/doc/html/draft-nishida-tcpm-agg-syn-ext-00>
> 
> 
> Please note that it may take a couple of minutes from the time of submission
> until the htmlized version and diff are available at tools.ietf.org <http://tools.ietf.org/>.
> 
> Internet-Drafts are also available by anonymous FTP at:
> ftp://ftp.ietf.org/internet-drafts/ <ftp://ftp.ietf.org/internet-drafts/>
> 
> 
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