[Bug 1752411] Re: bind9-host, avahi-daemon-check-dns.sh hang forever causes network connections to get stuck

[Laban Sköllermark]

I've run into this problem as well after upgrading my Ubuntu 17.10
installation (upgraded from 17.04) to Ubuntu 18.04 last week. My VPN
script calling "openconnect" hang and no packets got forwarded. My first
workaround was however to connect using nm-applet instead which worked
fine (available via package network-manager-openconnect-gnome).

I found this thread after a tip from a colleague after asking for help.
It would be nice to have a proper fix for users upgrading to Bionic. The
timeout fix/workaround would be good enough in my opinion.

@lathiat: Thanks for the fix in avahi-daemon-check-dns.sh (wrapping
"timeout" around the "host" call). I can confirm that this solves the
problem for me as well.

A note from my setup:
I have *two* stuck "host -t soa local." processes launched by two different "avahi-daemon-check-dns.sh" instances. pstree says that one is launched by "vpnc-script" (launched by openconnect) and the other one is launched by "01-ifupdown" launched by "nm-dispatcher". Killing the host process started by openconnect->vpnc-script solves the problem.

And as @marvin24 said, uninstalling "ifupdown" does *not* solve the
problem.

@muetze-bsw (in duplicate Bug #1772692): I can confirm that uninstalling
"avahi-daemon" solves the problem. This will be my "permanent"
workaround.

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Title:
  bind9-host, avahi-daemon-check-dns.sh hang forever causes network
  connections to get stuck

Status in avahi package in Ubuntu:
  Confirmed
Status in bind9 package in Ubuntu:
  Confirmed
Status in openconnect package in Ubuntu:
  Invalid
Status in avahi package in Debian:
  New

Bug description:
  On 18.04 Openconnect connects successfully to any of multiple VPN
  concentrators but network traffic does not flow across the VPN tunnel
  connection. When testing on 16.04 this works flawlessly. This also
  worked on this system when it was on 17.10.

  I have tried reducing the mtu of the tun0 network device but this has
  not resulted in me being able to successfully ping the IP address.

  Example showing ping attempt to the IP of DNS server:

  ~$ cat /etc/resolv.conf 
  # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
  #     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
  # 127.0.0.53 is the systemd-resolved stub resolver.
  # run "systemd-resolve --status" to see details about the actual nameservers.

  nameserver 172.29.88.11
  nameserver 127.0.0.53

  liam at liam-lat:~$ netstat -nr
  Kernel IP routing table
  Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
  0.0.0.0         192.168.1.1     0.0.0.0         UG        0 0          0 wlp2s0
  105.27.198.106  192.168.1.1     255.255.255.255 UGH       0 0          0 wlp2s0
  169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 docker0
  172.17.0.0      0.0.0.0         255.255.0.0     U         0 0          0 docker0
  172.29.0.0      0.0.0.0         255.255.0.0     U         0 0          0 tun0
  172.29.88.11    0.0.0.0         255.255.255.255 UH        0 0          0 tun0
  192.168.1.0     0.0.0.0         255.255.255.0   U         0 0          0 wlp2s0
  liam at liam-lat:~$ ping 172.29.88.11
  PING 172.29.88.11 (172.29.88.11) 56(84) bytes of data.
  ^C
  --- 172.29.88.11 ping statistics ---
  4 packets transmitted, 0 received, 100% packet loss, time 3054ms

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: openconnect 7.08-3
  ProcVersionSignature: Ubuntu 4.15.0-10.11-generic 4.15.3
  Uname: Linux 4.15.0-10-generic x86_64
  ApportVersion: 2.20.8-0ubuntu10
  Architecture: amd64
  CurrentDesktop: ubuntu:GNOME
  Date: Wed Feb 28 22:11:33 2018
  InstallationDate: Installed on 2017-06-15 (258 days ago)
  InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
  SourcePackage: openconnect
  UpgradeStatus: Upgraded to bionic on 2018-02-22 (6 days ago)

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