[Bug 1004775] Re: NetworkManager restarts dnsmasq and adds host route on every IPv6 route lookup

[Steve Langasek]

As I understand it, the NM SRU to precise updates the package to
unconditionally use the dbus interface for updates.  This means that the
package needs a versioned dependency on the SRU version of dnsmasq-base
that *enables* the dbus interface; otherwise this can break for users if
they happen to install the NM SRU without the dnmasq SRU.

I'm rejecting the package from the precise-proposed queue.  Mathieu, can
you please reupload with a fix for the dnsmasq versioned dependency?

** Description changed:

  [Impact]
  This issue affects all users of NetworkManager in a dual stack (IPv4 w/ IPv6 on the same network) environment. When any router advertisement is received, NetworkManager restarts dnsmasq in order to update the DNS configuration it uses.
  This change modifies the method of update of dnsmasq to use DBus methods instead of writing a configuration file; which avoids having to restart the daemon to re-read the configuration.
  
  kill -USR1 <dnsmasq pid> can be used to output to syslog the current DNS
  servers used by dnsmasq.
  
  [Test Case]
  1) Run NetworkManager in an dual-stack IPv4/IPv6 environment.
  2) Verify that dnsmasq does not get restarted when a router advertisement is received.
+ 3) Verify that DNS server settings are updated when stopping/starting a connection with NM.
  
  [Regression Potential]
  This change affects the underlying daemon used by NetworkManager to help with DNS resolution on the system. This daemon is updated via DBus. Since the method of update is changed; this may affect the resulting effective configuration of dnsmasq and break DNS resolution in case of a regression.
  
  ----
  
  NetworkManager stops and starts dnsmasq very frequently (every few
  minutes).  During the brief window that dnsmasq is restarting, hostname
  resolution doesn't work.  dnsmasq is getting restarted frequently enough
  that I see brief hostname resolution errors in Chrome several times a
  day during normal web browsing.
  
  This is on Precise with network-manager 0.9.4.0-0ubuntu4 and dnsmasq-
  base 2.59-4.
  
  The frequent restarts seem to be triggered by IPv6 route advertisements
  on my network.  (See log snippet below.)  When NetworkManager gets a
  route advertisement, it reconfigures everything.  In the case of
  dnsmasq, this means stopping dnsmasq, writing a new config file, and
  starting dnsmasq.  NetworkManager should restart dnsmasq only if it its
  configuration changes.
  
  I'm attaching a snippet from /var/log/daemon.log on my system that
  demonstrates a restart.  This is with debug logging configured in
  /etc/NetworkManager/NetworkManager.conf.

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Title:
  NetworkManager restarts dnsmasq and adds host route on every IPv6
  route lookup

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