Re: TCPv4 checksum errors

["David S. Miller" <davem@dm.cobaltmicro.com>]

   Date: Tue, 22 Dec 1998 11:01:13 +0100 (CET)
   From: Geert Uytterhoeven <Geert.Uytterhoeven@cs.kuleuven.ac.be>

   On Tue, 22 Dec 1998, David S. Miller wrote:
   > My suggestion is that since you can reproduce it, you should add code
   > next to this printk statement which dumps the entire packet in HEX to
   > the console.  Then you can see what and who is at fault and where.
   > If the packet is sufficiently small you can walk the checksum
   > algorithm by hand and verify it for this test case.

   Which one do I have to dump? skb->h.raw or skb->nh.raw? I guess
   skb->nh.iph->tot_len bytes at skb->nh.raw?

Look at what the code next to the printk is verifying:

		skb->csum = csum_partial((char *)th, len, 0);
		if (tcp_v4_check(th,len,skb->nh.iph->saddr,skb->nh.iph->daddr,skb->csum))

So you need all the bytes from 'th' to 'th + len'.  You also need the
values of the source and destination addresses from the IP header (at
skb->nh.iph->{saddr,daddr}).

Good luck.

Later,
David S. Miller
davem@dm.cobaltmicro.com

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