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

[Launchpad Bug Tracker]

This bug was fixed in the package isc-dhcp - 4.2.4-1ubuntu10.2

---------------
isc-dhcp (4.2.4-1ubuntu10.2) quantal-proposed; urgency=low

  * Fix isc-dhcp-server-ldap not actually containing ldap support.
    Thanks to Christian Hoffmann for tracking down the issue. (LP: #1071928)
  * Don't set fqdn.fqdn in dhclient.conf as that seems to confuse some DHCP
    servers. An alternative would have been to only set fqdn.fqdn and not
    host-name, but that appears to confuse another set of servers.
    For now go with just host-name which is the most common and if becomes a
    big problem for IPv6 (where fqdn.fqdn is apparently required), then we'll
    need to have a separate dhclient6.conf file and change all the calls to
    dhclient -6 to use that file instead. (LP: #1088682)
  * Include patch from RedHat/Fedora to deal with hardware/xen/virtio offload
    of UDP checksums. (LP: #930962)
 -- Stephane Graber <stgraber at ubuntu.com>   Fri, 01 Mar 2013 16:07:49 -0500

** Changed in: isc-dhcp (Ubuntu Quantal)
       Status: Fix Committed => Fix Released

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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:
  Fix Released
Status in “isc-dhcp” source package in Quantal:
  Fix Released

Bug description:
  == Rationale ==
  Machines using virtio (kvm/xen) and running a dhcp server in a VM won't receive the proper udp checksums which leads to dhcpd dropping the packets.
  This patch forces the checksum to be calculated in such case.

  == Test case ==
  1) Install a dhcp server in a VM using kvm/xen
  2) Make sure you don't have iptables re-calculating the checksums for you
  3) Check that the requests go through as expected

  == Regression potential ==
  Raring has had that fix for a while, so does redhat, so it looks pretty safe to me.


  --- original bug report ---
  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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