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checksum offloading

To: netdev@xxxxxxxxxxx
Subject: checksum offloading
From: francois donzet <fdonzet@xxxxxxxx>
Date: Mon, 10 Nov 2003 12:29:15 +0100 (CET)
Sender: netdev-bounce@xxxxxxxxxxx
Hi,

i have a little question : 

When tcp checksum offloading is enabled, the chip
computes a sum on all words of the packet contents and
stores the result in skb->csum, setting skb->ip_summed
to CHECKSUM_HW. (see for example, e100_main.c)

Then, when packet reaches tcp layer, via
tcp_checksum_init(), tcp checksum is verified (using
together skb->csum and the pseudo header checksum).

How does TCP deal with skb->csum, as it doesn't cover
only the tcpheader+data (but ipheader+tcpheader+data)

Thanks.



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