Comment 6 for bug 930962
Revision history for this message
| Michal Suchanek (hramrach) wrote Re: [Bug 930962] Re: dhcp3-server reports many bad udp checksums to syslog using virtio NIC | #6 |
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1b1ed1a
(Get the code!)
On 8 August 2012 18:35, Stefan Bader <email address hidden> wrote:
> Finally got some time to look into this. As much as my test reproduction
> of this goes it would be not critical in importance because clients seem
> to get an IP address even with those messages showing up.
That's not what I see here, they do not get an IP address.
>
> I can see those bad crc messages in (Quantal, Precise and Lucid those
> just been the ones I set up to try). To summarize my understanding here:
>
> - virtio (and xen netfron) would deliberately leave the checksum incomplete for
> packets between interfaces on the same host because the packet will always
> remain in memory. So calculating a checksum is a waste of time.
No, that's how any network card with checksum offloading behaves. It
may skip copying the checksum because it verified it already, and the
virtio device abuses this interface quirk to never produce any
checksum in the first place. On real network interfaces you can turn
that feature off, and then the checksum is always copied. On virtio
'turning off' would amount to producing a checksum which dhclient can
subsequently check.