Comment 7 for bug 930962
Revision history for this message
| Stefan Bader (smb) wrote Re: [Bug 930962] Re: dhcp3-server reports many bad udp checksums to syslog using virtio NIC | #7 |
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73416ba
(Get the code!)
On 09.08.2012 10:21, Michal Suchanek wrote:
>> 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.
Then what is your exact setup?
>> - 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.
Yes, it a real card has checksum offloading it would do this in hardware. What I
try to say is that the fact that virtio leaves them incomplete when passed
within the virtual network looks like a deliberate decision there for
performance improvement. And since upstream has added that interface to check
for those incomplete checksums (and specifically mentioning dhcp) makes it clear
that the drivers will not change.