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SubjectRe: hardware checksumming
Date
oh its me again. sorry but the message bofore was messed up. so lets try 
again.

On Thursday 23 August 2001 15:54, you wrote:
> > is hardware support by a NIC for checksum generation / offloading not
> > quite usless? the checksumming enging can only be used when UDP/TCP
> > packets are <= the MTU of the NIC (e.g 1500 bytes).
>
> checksums can be chained.
yes that might be easy for the NIC's transmitting enging when all fragments
belonging together come one after the other in the transmit-ring.
but receiving is difficult since different connections can arrive
simultanously and reslut in interleaved framgents.

something else: you need quite a lot of ram on the NIC to buffer fragments.
if not it will have to transfer the data twice through the PCI (checksumm are
at the beginig of a packet not the end). nobody did spend a second on
thinking to implement all in hardware when the interet protokol was desinged.

do you know any NIC that is capable of chaining? currenty i've a dp83820
on my desc and at the moment im not eaven shure if checksumming can
be chained over multiple descriptions (describing one single ethernet frame).

>
> > i expact that UDP/TCP packets are in general bigger than that or is
> > exactly
>
> TCP packets are certainly never larger than the MTU.

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