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

[Mathieu Trudel-Lapierre]

** 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.
+ 
+ [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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https://bugs.launchpad.net/bugs/1004775

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

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