Re: [tcpm] Faster application handshakes with SYN/ACK payloads

"Adam Langley" <> Tue, 15 July 2008 18:29 UTC

Return-Path: <>
Received: from [] (localhost []) by (Postfix) with ESMTP id B53EC3A6B3A; Tue, 15 Jul 2008 11:29:20 -0700 (PDT)
Received: from localhost (localhost []) by (Postfix) with ESMTP id 4BEA93A6B5A for <>; Tue, 15 Jul 2008 11:29:19 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.977
X-Spam-Status: No, score=-1.977 tagged_above=-999 required=5 tests=[BAYES_00=-2.599, FM_FORGED_GMAIL=0.622]
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id VRBPXUyRUx+0 for <>; Tue, 15 Jul 2008 11:29:18 -0700 (PDT)
Received: from ( []) by (Postfix) with ESMTP id 91B603A6AF6 for <>; Tue, 15 Jul 2008 11:29:18 -0700 (PDT)
Received: by with SMTP id b25so4708442rvf.49 for <>; Tue, 15 Jul 2008 11:29:46 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=gamma; h=domainkey-signature:received:received:message-id:date:from:sender :to:subject:cc:in-reply-to:mime-version:content-type :content-transfer-encoding:content-disposition:references :x-google-sender-auth; bh=ul24djLZIahrWv9+09+rwZxQaZ1AxZH4FGCnZYtL/yk=; b=YYGdQnzAAwIm7NYwjS9Bta+46euNdFKtU2S/2ncpNry/0MtbnkUOp6udwPueG+v+VD XjH77X+mMQ57ImeAgkd7SQTt54+Z3SzW7q0kOqsxTGK0Pyb/BeGpv9nv59+0uOQjtsZs Z63TPQehPkxDk5mOOdabnFj7e+i6MyTnsMa4I=
DomainKey-Signature: a=rsa-sha1; c=nofws;; s=gamma; h=message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references:x-google-sender-auth; b=dYDYe0KjI1QK3O5o1adYp9GYY1DGhDgtwKDU/HBFzoYwXARQ8i2dbVAehzLlrsE/aq aq4PzNpIkIwwN670K2QGrTgpY4qbs9eTAcNC9fMwmiumHJqA836UikOUi8LofkQRkOqd O0D1VWUbFaKSwTrrwemUlIaQc/yy0xKZQ+Y7o=
Received: by with SMTP id b18mr7647172rvl.159.1216146585912; Tue, 15 Jul 2008 11:29:45 -0700 (PDT)
Received: by with HTTP; Tue, 15 Jul 2008 11:29:45 -0700 (PDT)
Message-ID: <>
Date: Tue, 15 Jul 2008 11:29:45 -0700
From: Adam Langley <>
To: Lloyd Wood <>
In-Reply-To: <>
MIME-Version: 1.0
Content-Disposition: inline
References: <> <>
X-Google-Sender-Auth: e7faaf52b09507fd
Subject: Re: [tcpm] Faster application handshakes with SYN/ACK payloads
X-Mailman-Version: 2.1.9
Precedence: list
List-Id: TCP Maintenance and Minor Extensions Working Group <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit

On Tue, Jul 15, 2008 at 11:22 AM, Lloyd Wood <> wrote:
> This looks awfully like reinventing transactional TCP to me - and IIRC the
> reason that never got widely adopted was the increased potential for DOS
> attacks by tying up memory early on with a loaded SYN.
> What am I missing?

There's a short section in the draft comparing it to T/TCP, but the
quick version:
  * For a given SYN there's one bit of additional state required (and
the draft says that a host can completely ignore a SYNACK Payload
Permitted bit if it's under heavy load and using cookies etc)
  * There's no payload in the SYN, so you can't send data to an
application from an unverified source address

In short, I don't believe that any of the T/TCP objections apply to
this draft, although I could be wrong. I suggest that the similarities
with it are only superficial.



Adam Langley
tcpm mailing list