Message-ID: <52E6AA0B.1050600@bogus.com>
Date: Mon, 27 Jan 2014 10:48:43 -0800
From: joel jaeggli <joelja@bogus.com>
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To: Joe Touch <touch@isi.edu>, "stbryant@cisco.com" <stbryant@cisco.com>
References: <201401240320.s0O3KsR9013700@maildrop2.v6ds.occnc.com>
 <52E2BBC0.2030203@isi.edu> <52E68C12.2050308@cisco.com>
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Cc: "mpls@ietf.org" <mpls@ietf.org>, IETF discussion list <ietf@ietf.org>
Subject: Re: [mpls] Last Call: <draft-ietf-mpls-in-udp-04.txt> (Encapsulating
 MPLS in UDP) to Proposed Standard
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On 1/27/14, 8:48 AM, Joe Touch wrote:
> Those same mechanisms have provided hardware checksum support for a ver=
y long time.=20


The new header and the payload are actually in different parts of the
forwarding complex until they hit the output queue, you can't checksum
data you don't have.

> Joe
>=20
>> On Jan 27, 2014, at 8:40 AM, Stewart Bryant <stbryant@cisco.com> wrote=
:
>>
>>> On 24/01/2014 19:15, Joe Touch wrote:
>>>
>>>> This eliminates the "expands the reach of MPLS argument".
>>>>
>>>> First UDP checksums:
>>>>
>>>>   The UDP checksum is at the beginning of the payload.  Please see
>>>> http://www.ietf.org/mail-archive/web/mpls/current/msg11279.html
>>>>   This makes filling in a new UDP checksum infeasible on most high e=
nd
>>>>   hardware.
>>>
>>> That argument would make sense if most hardware wasn't store-and-forw=
ard on a per-packet basis.
>> They may be store and forward, but most of the high end designs
>> use multiple grades of memory putting the packet in "slow memory"
>> and providing a snapshot of the header in "fast memory" to the
>> forwarder. Thus although the whole packet is in the system, it
>> it is not accessible to the engine that would need to calculate the
>> c/s.
>>
>> Stewart
>=20



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