Re: hardware checksumming

[Helge Hafting <helgehaf@idb.hist.no>]

Christian Widmer wrote:

> 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.

You don't have to store entire fragments in a NIC to do
hw checksums.  All you need to store is the partial checksums,
and add to them whenever yet another fragment comes in for
that packet.

Helge Hafting