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

[Stewart Bryant <[e-mail]>]

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