[Bug 930962] Re: dhcp3-server reports many bad udp checksums to syslog using virtio NIC

[Michal Suchanek]

On 9 August 2012 10:49, Stefan Bader <stefan.bader at canonical.com> wrote:
> 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?

dnsmasq running on xen dom0 and xen dumUs trying to get IP address
with dhcp client.

I see server mentioned here so maybe on server the checksum error is
not considered fatal.

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https://bugs.launchpad.net/bugs/930962

Title:
  dhcp3-server reports many bad udp checksums to syslog using virtio NIC

Status in “isc-dhcp” package in Ubuntu:
  Confirmed

Bug description:
  Tested with  dhcp3-server ver. 3.1.3-2ubuntu3.3  in Ubuntu 10.04.3
  Server, x64.

  The DHCP server reports that UDP packets sent to it have bad
  checksums:

  Feb 11 06:57:18 ... dhcpd: 5 bad udp checksums in 5 packets
  Feb 11 06:58:22 ... dhcpd: last message repeated 7 times
  Feb 11 06:59:17 ... dhcpd: last message repeated 7 times

  The DHCP server host is a KVM virtual machine using a virtio-based
  virtual NIC.

  This problem has been reported for other distros using KVM and virtio:

  https://bugs.mageia.org/show_bug.cgi?id=1243

  http://www.mail-archive.com/kvm@vger.kernel.org/msg41958.html
   - suggests using iptables to write in a checksum

  http://pkgs.fedoraproject.org/gitweb/?p=dhcp.git;a=blob;f=dhcp-4.2.2-xen-checksum.patch;h=038d346d726e131f1ab2579fe015a72b49733a0d;hb=HEAD
   - Fedora patch to dhcp to avoid this

  The simplest workaround is to change the virtual NIC type from virtio
  to Intel e1000 in KVM. Apparently this driver calculates checksums.
  But virtio is the default driver type.

  Thanks,
  Tim Miller Dyck

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