[pkg-dhcp-devel] Bug#353161: isc-dhcp-server: RX/TX checksum offloading for virtual causes ISC DHCP Server to fail

[Arne Schwabe]

Package: isc-dhcp-server
Version: 4.1.ESV-R4-0ubuntu5.2
Followup-For: Bug #353161

Dear Maintainer,

 This also happens in a kvm setup if both server and client are kvm machines. The problem is very simple. To support NIC offloading and conserve CPU time the correct UDP check is only generated when the packets actually transerve the physical NIC of the kvm setup. If a packet goes from one KVM machine to another KVM machine the flag that the checksum is correct is set by the virtual NIC driver of the receiving kvm (like it is done if real rx checksum checking is done by the hardware NIC). The ISC DHCP Server (in my case) or ISC Relay agent (in the original bug report) calculates the checksum on its own which does not work. I think the loopback device the check is also never calculated. 

Arne
P.S.: Yes, I know that I am using Ubuntu and this a debian bug tracker but I think it is irrelevant for this bug.


-- System Information:
Debian Release: wheezy/sid
  APT prefers precise-updates
  APT policy: (500, 'precise-updates'), (500, 'precise-security'), (500, 'precise')
Architecture: amd64 (x86_64)

Kernel: Linux 3.2.0-29-virtual (SMP w/1 CPU core)
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages isc-dhcp-server depends on:
ii  adduser                3.113ubuntu2
ii  debconf [debconf-2.0]  1.5.42ubuntu1
ii  debianutils            4.2.1ubuntu2
ii  isc-dhcp-common        4.1.ESV-R4-0ubuntu5.2
ii  libc6                  2.15-0ubuntu10
ii  libcap2                1:2.22-1ubuntu3
ii  lsb-base               4.0-0ubuntu20
ii  upstart [upstart-job]  1.5-0ubuntu7

isc-dhcp-server recommends no packages.

Versions of packages isc-dhcp-server suggests:
pn  apparmor              <none>
pn  isc-dhcp-server-ldap  <none>

-- Configuration Files:
/etc/dhcp/dhcpd.conf changed [not included]

-- debconf information excluded