Re: [regression] 2.6.37+ commit 0363466866d9.... breaks tcp ipv6

Eric Dumazet
2011-01-21T19:55:50Z

Le vendredi 21 janvier 2011 à 20:47 +0100, Hans de Bruin a écrit :
> On 01/18/2011 11:03 PM, Eric Dumazet wrote:
> > Le mardi 18 janvier 2011 à 22:42 +0100, Hans de Bruin a écrit :
> >> On 01/18/2011 09:06 PM, Jesse Gross wrote:
>
> ...
>
> > You could try "tcpdump -i eth0 ip6 -v"
> >
> > I guess you receive frames with bad checksums
>
> While you where staring at the code, I was fooling around with tcpdump.
> And while the problem is fixed, I still have some questions:
>
> Is there tool which shows whether a nic supports ipv6 checksum offload
> or not?
>
> I have captured http traffic (wget http://bootes/) between psion (my git
> tree following laptop) and bootes (something running 2.6.33.7).
> Attached is a capture with psion running 2.6.37 and one with this
> morning's git tree. Wat's with the 'chsum ... ( incorrect -> ' lines ?
> ifconfig does not show errors on either of the machines.
>

tcpdump gets a copy of outgoing frames before NIC performs tx checksum
(if tx checksum handled by NIC), so it's normal to have "bad checksums"
on TX, unless you disable tx offloading (ethtool -K eth0 tx off)

I was referring to check with tcpdump incoming frames, because invalid
checksums in RX is sign that other peer sent wrong checksums