Re: [tcpm] TCP EDO and SYN-EXT-OPT finalization - request for discussion

Yoshifumi Nishida <> Thu, 14 October 2021 01:51 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id 986703A17CA for <>; Wed, 13 Oct 2021 18:51:30 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2.098
X-Spam-Status: No, score=-2.098 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, HTML_MESSAGE=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (2048-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id nJhBDEgOI25I for <>; Wed, 13 Oct 2021 18:51:25 -0700 (PDT)
Received: from ( [IPv6:2607:f8b0:4864:20::834]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 948603A17F9 for <>; Wed, 13 Oct 2021 18:51:24 -0700 (PDT)
Received: by with SMTP id c20so4501206qtb.2 for <>; Wed, 13 Oct 2021 18:51:24 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=1zAgBLOugpePbRLJ78PYH85uIOwxwfH/7KYl4uMkey0=; b=fhm8sjlpxh4qzmX4CjHpdGJ+zCrwZINZ3vhYmlvW85BLg854MwCQoR5CWRoTaNtGfn Xj/tyUuGZoIDCidJD8GATR3kNSOsksUkUX6ieW65FDIB72HtqAihnOzKBZdahVhwGRhm bmTFuvMfNclLCX+XkAB5oVK0on+xRdoL29Rl7cUPAHVCak3pGXQRSoabxilc0cZ5wUGV gblWoR1SvGqgt6KiZbUp3nApqNl2rhMCkVai+BSnJJH90oo2tAHe13iUU67BKBQygLZF dPus+/tIkmVmcz21Il3UT4HsQaL8OmKhsgNdG7ni2a2SNvUP4vmTrCPAk2YzcQaaFy2f r0wQ==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=1zAgBLOugpePbRLJ78PYH85uIOwxwfH/7KYl4uMkey0=; b=11JtDySqibjl8KVnSOxhPleEmgkTnhNF2YRj3taSd4A0UPoWZEGiUSi+m86YUvgd1e aptE31TW25TMTEO6ur502o/CpjYTZwbJHNHXFANxp+u5TkXHTBSSm5m3WIaT82NxCYno pAH7kJxCTrIdcMTXmi7Xf7L4ris98Dk3Tm4GUOx8lA8EXnz869E5ItRJBWwG0umABKFD DzjMp5ttLKgCaT/FFhu/rUwzjTcmIogaGz1CHAJxeQCUBdPtgwTyt8RaDbnHcFghEoBv fdmEhyYZpU1DdMFYXgr3XXd+9jLFmo0pOPV2bFFmB57rleypfO0YHAe8hDV4M5OEoXcS /gIw==
X-Gm-Message-State: AOAM532TTNgN/zoOJtMxFwFlTAGVbx8w/fyYNrp1xAGJhTMi80Rh5QGj YH0kUEp0D0XYlPcB0urVVg4AKkCixH66Xiam2BA=
X-Google-Smtp-Source: ABdhPJy9nYUZ+MGCPC8p1DYxWIB2DUALZvEawiKFeVt0ZKKyxuKhRAl07mSABO0H/rv/c/OZmA2oJjpddPfXZ4JDgNc=
X-Received: by 2002:a05:622a:4d2:: with SMTP id q18mr3365270qtx.84.1634176283291; Wed, 13 Oct 2021 18:51:23 -0700 (PDT)
MIME-Version: 1.0
References: <> <> <23584_1634116047_6166A1CF_23584_209_1_787AE7BB302AE849A7480A190F8B93303542B124@OPEXCAUBMA2.corporate.adroot.infra.ftgroup> <> <>
In-Reply-To: <>
From: Yoshifumi Nishida <>
Date: Wed, 13 Oct 2021 18:51:12 -0700
Message-ID: <>
To: "" <>
Cc:, tcpm <>
Content-Type: multipart/alternative; boundary="000000000000ddc03f05ce465060"
Archived-At: <>
Subject: Re: [tcpm] TCP EDO and SYN-EXT-OPT finalization - request for discussion
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: TCP Maintenance and Minor Extensions Working Group <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Thu, 14 Oct 2021 01:51:31 -0000

Hi Joe,

On Wed, Oct 13, 2021 at 9:01 AM <>

> Hi, Yoshi,
> Although I noticed that post, there are two issues that make it not really
> comparable to SYN-EXT:
> - SYN-EXT extends the space available to all options, whereas AGG-SYN
> compresses existing options
> a single option of larger than 40 bytes can be supported in the former but
> not the latter
> - SYN-EXT is compatible with connections to legacy receivers; AGG-SYN does
> not appear to be
> a SYN-EXT endpoint can put the options it expects/needs in the SYN with a
> 2-byte SYN-EXT option overhead
> by compressing existing options, AGG-SYN effectively redesigns TCP such
> that legacy receivers would require an additional round-trip to recover
> One you have anything like the AGG-SYN option in a SYN, you’ve effectively
> redesigned TCP and can do anything you want, as the doc suggests - add
> additional RTTs for coordinate, etc. But that comes at the expense of
> legacy receivers and middle boxes, which can no longer rely on tracking the
> existing 3-way handshake.
> Once you’ve taken that step, you might as well just use a new transport
> code point and design a new protocol…

While I understand your points, I would like to mention that the method
proposed in the draft is basically the same as what mptcp already does.
If this looks like designing a new protocol, I think mptcp can also be
viewed as a new protocol. (you may say so, though..)
So, I'm not very sure delaying option negotiation looks like a more drastic
change than using OOB packets.

Also, I am not sure which one is more legacy receiver friendly as both
approach send a new option kind in the first SYN and the feature is
disabled if the option is ignored.