Re: [tcpm] Catalog approach for syn option aggregation draft

Hi Yoshi,

Regarding the MSS: Isn’t the MSS for IPv6 only 1440 byte?

Just as a thought: Instead of encoding an MSS value, 1 bit could be used to convey “if set to 1, use the maximum MSS for the Ethernet MTU of 1500 byte”?

Disclaimer: I haven’t thought about the implications on IPv4/IPv6 translation techniques. But, anyway, the bigger problem may be the installed base of MSS clamping…

Michael

From: tcpm <tcpm-bounces@ietf.org> On Behalf Of Yoshifumi Nishida
Sent: Friday, July 7, 2023 8:40 AM
To: tcpm@ietf.org Extensions <tcpm@ietf.org>
Subject: [tcpm] Catalog approach for syn option aggregation draft

Hi folks,

During my presentation for syn aggregation draft in the last WG meeting, some folks suggested using a catalog approach to compress existing options such as MSS, wscale, etc.
I am still thinking, but I've put some initial ideas about this approach in the updated version of the draft.

In a nutshell, the idea is to use entire bits for 'Group 1'. As one group can carry 6 bits, we use 4 bits for window scale option, 1 bit for SACK-permit and another 1 bit for MSS.
As window scale value ranges from 0 to 14, we can accomodate all values in 4 bits.
SACK-permit carries 1 bit information, so using 1 bit is enough.
MSS is a bit tricky as it can carry various values. But, as far as I've checked 24M syn packets in CAIDA and WIDE's packet captures, over 40% MSS options in SYN packets carries 1460.
Hence, the draft uses 1 bit to indicate MSS=1460.

Since I'm still wondering if this format is fine or there might be more efficient ways, your feedback is highly appreciated.
If you're interested, please check the updated draft.
Thank you so much!
--
Yoshi

---------- Forwarded message ---------
From: <internet-drafts@ietf.org<mailto:internet-drafts@ietf.org>>
Date: Wed, Jul 5, 2023 at 1:24 AM
Subject: I-D Action: draft-nishida-tcpm-agg-syn-ext-04.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-04.txt
   Pages           : 11
   Date            : 2023-07-05

Abstract:
   TCP option space is scarce resource as its maximum 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 can aggregate multiple TCP options in SYN
   segments into a single option so that more options can be negotiate
   during 3-way handshake.  With its simple design, the approach does
   not require fundamental changes in TCP.

The IETF datatracker status page for this Internet-Draft is:
https://datatracker.ietf.org/doc/draft-nishida-tcpm-agg-syn-ext/

There is also an HTML version available at:
https://www.ietf.org/archive/id/draft-nishida-tcpm-agg-syn-ext-04.html

A diff from the previous version is available at:
https://author-tools.ietf.org/iddiff?url2=draft-nishida-tcpm-agg-syn-ext-04

Internet-Drafts are also available by rsync at rsync.ietf.org::internet-drafts

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