[Bug 1959847] Re: Unknown operation (12) 0x0240 Unknown (7680)[Malformed Packet]

[Felipe Reyes]

On Tue, 2022-02-08 at 15:11 +0000, Frode Nordahl wrote:
> Thank you for your bug report, I wonder if this proposed fix [0] could
> be related?

I don't believe so, IIUC this would affect how the replies are
assembled and passed to the guest. I was looking at a similar issue (RR
counters) on the systemd-resolved side[0] and systemd would be logging
"invalid reply" while we see ETIMEDOUT.

> 
> Does tshark provide any detail about what exactly it finds malformed
> about the packets?

yes, the opcode is 12, where a query's opcode is 0 , opcode 12 is
unassigned according to the spec -
https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-5

[0] https://github.com/systemd/systemd/issues/12841

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https://bugs.launchpad.net/bugs/1959847

Title:
  Unknown operation (12) 0x0240 Unknown (7680)[Malformed Packet]

Status in ovn package in Ubuntu:
  Triaged

Bug description:
  There have been DNS issues while running CI jobs for the openstack
  charms, when I captured the dns traffic in one of the nova-compute
  units[0][1], it can be seen how certain queries are malformed:

   ~ $ tshark -r dns-port-53.pcap  | grep -i malformed | tail -n 2
  15403 3602.706021 10.245.160.32 → 10.245.160.114 DNS 126 Unknown operation (12) 0x0240 Unknown (7680)[Malformed Packet]
  15404 3602.706023 10.245.160.32 → 10.245.160.114 DNS 126 Unknown operation (12) 0x0240 Unknown (7680)[Malformed Packet]
   ~ $ tshark -r dns-port-53.pcap  | grep -i malformed | wc -l
  408
   ~ $ tshark -r dns-port-53.pcap  | wc -l
  15728

  Another symptom found is within the VM's systemd-resolved, it logs
  queries timing out https://pastebin.ubuntu.com/p/pJnd9sprpF/ [2]

  
  Packages installed:

  # dpkg -l ovn-common
  Desired=Unknown/Install/Remove/Purge/Hold
  | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
  |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
  ||/ Name           Version                    Architecture Description
  +++-==============-==========================-============-=================================
  ii  ovn-common     20.03.2-0ubuntu0.20.04.2.0 amd64        OVN common components

  # apt policy ovn-common
  ovn-common:
    Installed: 20.03.2-0ubuntu0.20.04.2.0
    Candidate: 21.12.0-0ubuntu1.0~20.04.0
    Version table:
       21.12.0-0ubuntu1.0~20.04.0 500
          500 http://ppa.launchpad.net/fnordahl/serverstack/ubuntu focal/main amd64 Packages
   *** 20.03.2-0ubuntu0.20.04.2.0 500
          500 http://ppa.launchpad.net/fnordahl/lp1857026/ubuntu focal/main amd64 Packages
          100 /var/lib/dpkg/status
       20.03.2-0ubuntu0.20.04.2 500
          500 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
       20.03.0-0ubuntu1 500
          500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages

  [0] tcpdump -i any -ln port 53
  [1] https://private-fileshare.canonical.com/~freyes/dns-port-53.pcap
  [2] note: this is a different run from the tcpdump capture, so they could be different root causes

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