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Re: [mpls] Last Call: <draft-ietf-mpls-in-udp-04.txt> (Encapsulating MPLS in UDP) to Proposed Standard

Joe Touch <touch@isi.edu> Mon, 27 January 2014 16:49 UTC

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From: Joe Touch <touch@isi.edu>
Date: Mon, 27 Jan 2014 08:48:35 -0800
To: "stbryant@cisco.com" <stbryant@cisco.com>
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Subject: Re: [mpls] Last Call: <draft-ietf-mpls-in-udp-04.txt> (Encapsulating MPLS in UDP) to Proposed Standard
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Those same mechanisms have provided hardware checksum support for a very long time. 

Joe

> 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 end
>>>   hardware.
>> 
>> That argument would make sense if most hardware wasn't store-and-forward 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

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