Re: [tcpm] draft-anumita-tcpm-stronger-checksum

Joe Touch <touch@isi.edu> Thu, 10 June 2010 21:21 UTC

Return-Path: <touch@isi.edu>
X-Original-To: tcpm@core3.amsl.com
Delivered-To: tcpm@core3.amsl.com
Received: from localhost (localhost [127.0.0.1]) by core3.amsl.com (Postfix) with ESMTP id 91D563A69AA for <tcpm@core3.amsl.com>; Thu, 10 Jun 2010 14:21:45 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.392
X-Spam-Level:
X-Spam-Status: No, score=-1.392 tagged_above=-999 required=5 tests=[AWL=1.207, BAYES_00=-2.599]
Received: from mail.ietf.org ([64.170.98.32]) by localhost (core3.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id tCJFAbR3RN7O for <tcpm@core3.amsl.com>; Thu, 10 Jun 2010 14:21:44 -0700 (PDT)
Received: from vapor.isi.edu (vapor.isi.edu [128.9.64.64]) by core3.amsl.com (Postfix) with ESMTP id 22C8E3A69A3 for <tcpm@ietf.org>; Thu, 10 Jun 2010 14:21:44 -0700 (PDT)
Received: from [75.213.115.189] (189.sub-75-213-115.myvzw.com [75.213.115.189]) (authenticated bits=0) by vapor.isi.edu (8.13.8/8.13.8) with ESMTP id o5ALJkhE016684 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT); Thu, 10 Jun 2010 14:19:58 -0700 (PDT)
Message-ID: <4C1156F2.9030600@isi.edu>
Date: Thu, 10 Jun 2010 14:19:46 -0700
From: Joe Touch <touch@isi.edu>
User-Agent: Thunderbird 2.0.0.24 (Windows/20100228)
MIME-Version: 1.0
To: "Biswas, Anumita" <Anumita.Biswas@netapp.com>
References: <A3D02FB7C6883741952C425A59E261A5097324A2@SACMVEXC2-PRD.hq.netapp.com>
In-Reply-To: <A3D02FB7C6883741952C425A59E261A5097324A2@SACMVEXC2-PRD.hq.netapp.com>
X-Enigmail-Version: 0.96.0
Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="------------enig4CDB1563777154EA5D90BE91"
X-ISI-4-43-8-MailScanner: Found to be clean
X-MailScanner-From: touch@isi.edu
Cc: tcpm@ietf.org, "Anantha Ramaiah (ananth)" <ananth@cisco.com>
Subject: Re: [tcpm] draft-anumita-tcpm-stronger-checksum
X-BeenThere: tcpm@ietf.org
X-Mailman-Version: 2.1.9
Precedence: list
List-Id: TCP Maintenance and Minor Extensions Working Group <tcpm.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/listinfo/tcpm>, <mailto:tcpm-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/tcpm>
List-Post: <mailto:tcpm@ietf.org>
List-Help: <mailto:tcpm-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/tcpm>, <mailto:tcpm-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 10 Jun 2010 21:21:46 -0000


Biswas, Anumita wrote:
...
>>> If keeping the standard TCP CRC intact (and covering TCP header & 
>>> data) and having an RFC1146 alternate checksum that works 
>> differently 
>>> than defined therein, perhaps it would be better to make it 
>> a new TCP 
>>> option then.
>>
>> Defined therein where? 
>
> http://datatracker.ietf.org/doc/draft-anumita-tcpm-stronger-checksum/
> 
> Section 3 - "Negotiating the use of CRC 32C"

There are two differences:

a) different processing rules
	computed over different portions of the segment
	and
	different rules for what happens to the original TCP checksum area
	and
	different rules for what to do when the option fails on SYNs

These are hard to fix without rewriting RFC-1146, which is feasible only if
there is a real need.

b) different algorithm
	this is easily fixed without modifying RFC-1146, by
	defining a new algorithm

	this assumes only the algorithm changes, though

Joe