Ubuntu
isc-dhcp package

  1. Bug #930962
  2. Comment #19

Comment 19 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

On 7 January 2013 23:13, Martijn Lievaart <email address hidden> wrote:
> According to my cursory reading of relevant RFCs and a quick wireshark
> session, the bug is in KVM virtio. An UDP packet should contain a
> checksum field of 0 for no checksum, or a correct checksum. I see bogus
> values coming in.
>
> OTOH, wireshark warns that this may be due to offloading, so I may not
> be correct in this analysis.
>

This is due to virtio implementing 'offloading' by returning random
garbage in the checksum field.

Since the code to calculate the checksumis not present this offloading
cannot be turned off.

Since kernel has interface to inform applications that offloading is
on it is a bug in the application to interpret the bogus checksum.
Presumably the card has already checked it and did not bother passing
it on.

This same feature is available on real e1000 hardware and can be
turned off there.