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

[Stefan Bader]

Right, so all the hosts I use already have this in "sudo iptables -L -t
mangle"

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination         
CHECKSUM   udp  --  anywhere             anywhere             udp dpt:bootpc CHECKSUM fill

I suspect this is added in some way by libvirt (which I have installed
on all of them). Manually this would be done by:

sudo iptables -A POSTROUTING -t mangle -p udp --dport bootpc -j CHECKSUM
--checksum-fill

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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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