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

[Stefan Bader]

On 09.08.2012 11:17, Michal Suchanek wrote:

>> Then what is your exact setup?
> 
> dnsmasq running on xen dom0 and xen dumUs trying to get IP address
> with dhcp client.

Ah ok, I was using the isc-dhcp-server on a KVM guest to isc-dhcp-clinet on
another one.

But thought I also had been using the dnsmasq setup created by libvirt for Xen
dom0 to domU. Hm, wait, I may have seen something somewhere in all those links
and reports that mentioned libvirt having a quirk for that. Are you using
dnsmasq on your own or have libvirt in use?

(If libvirt does something it probably is the ipfilter based approach that is
mentioned in a few placec)
> 
> I see server mentioned here so maybe on server the checksum error is
> not considered fatal.

The handling should be the same on server or on desktop. But then, maybe network
manager is doing something when it sees the checksum errors. That would not be
happening on server.

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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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