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@xxxxxxxxx> 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