Finally got some time to look into this. As much as my test reproduction
of this goes it would be not critical in importance because clients seem
to get an IP address even with those messages showing up.
I can see those bad crc messages in (Quantal, Precise and Lucid those
just been the ones I set up to try). To summarize my understanding here:
- virtio (and xen netfron) would deliberately leave the checksum incomplete for
packets between interfaces on the same host because the packet will always
remain in memory. So calculating a checksum is a waste of time.
- There has been a kernel change that allows to check the checksum status
([PACKET]: Add optional checksum computation for recvmsg). This has been in
the kernel since 2.6.26.
- The isc-dhcp code needs to be updated to use this new interface. It seems
that the
patch from Fedora was added about a year ago but would still apply to the
latest
Debian package. Whether it never was attempted to forward this to the
isc-dhcp
project, or whether it was rejected for some reason, I don't know.
I am working on updates for the Quantal and Precise packages (Lucid
should follow but that needs a bit more work to apply the patch). But
then we also should investigate why this is not upstream or at least in
Debian.
** Changed in: isc-dhcp (Ubuntu)
Importance: Undecided => Medium
** Changed in: isc-dhcp (Ubuntu)
Assignee: (unassigned) => Stefan Bader (stefan-bader-canonical)
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https://bugs.launchpad.net/bugs/930962
Title:
dhcp3-server reports many bad udp checksums to syslog using virtio NIC
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