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"Bonjour" service may cause issues in resolving DNS names in the .local zone
Published Date : 06 Dec 2012   Content Ref: TEC3015691  





Symptoms

On a computer running the Bonjour service, which then connects to the Internet via a proxy server with a name in the .local DNS zone (such as "proxy.local"), connectivity may be very slow, or appear to be completely unresponsive.

The best diagnostic of this problem is to attempt to carry out an image search via Google or Bing using Internet Explorer - the first dozen or so results will be returned slowly, and no additional images displayed (only a grey box is shown).

Connectivity via other browsers (such as Chrome) may be unaffected, and return the image search results in the expected timeframe.

It is possible that you may also experience connectivity issues to other services in the .local namespace (such as RMDatabase or RMAuditor), although this has not been fully confirmed.



Cause

Bonjour is Apple's implementation of "zero configuration networking", intended to allow cross-network communication between devices with little or no user input.  As part of that implementation, it runs a multicast Domain Name Server service (mdns.exe) which advertises and responds to requests for the .local namespace.

Consequently, actual requests to connect to any names in the DNS .local zone (such as "proxy.local") are intercepted by the Bonjour service, which attempts to resolve the name to an IP address - this times out (since Bonjour is unaware of anything by that name), and passed on to the actual DNS server.  This causes an overhead of approximately 4 seconds whenever resolving proxy.local.

Image searches via Internet ExplorerŽ 9 (IE9) seem to suffer most heavily from this issue, presumably due to the high number of proxy connections generated.  Other browsers (such as Chrome) continue to run as expected, however - this may be down to the Bonjour services interaction with Internet Explorer, or the proxy "pre-fetch" behaviour implemented in IE9.



Procedure

Confirming that Bonjour mdns.exe is the root cause

To confirm that Bonjour is at the root of your issue:

  1. Open the services control panel (services.msc) on an affected computer, and look for a service called either "Bonjour" or "##Id_String1.6844F930_1628_4223_B5CC_5BB94B879762##" - if neither of these is present, the Bonjour service is not running on this computer, and the root cause of any issue lies elsewhere.
  2. If one of those services is listed, change the startup type to "Disabled" and stop the service.
  3. Browse to the folder C:\Program Files\Bonjour and rename the files mdnsresponder.exe and mdnsnsp.dll by adding ".old" to the end of the filename.
  4. Reboot the computer and re-test - if browser behaviour is now as expected, previous issues have been caused by Bonjour.

Alternatively, you can determine if resolution of the .local zone is an issue by:

  • Changing the browsers proxy settings to refer to the server by IP address instead of by name.


More Information

The Bonjour service is installed and enabled by Adobe CS, and Apple iTunes. It may also be installed by other software which we are not aware of - the steps above to determine if it is the root cause will still be valid, regardless of where the service has been installed from.

Links with additional detail

Apple support article on the behaviour of the Bonjour mdns responder - http://support.apple.com/kb/HT3473

Wikipedia article on the .local zone, and its use by Bonjour - http://en.wikipedia.org/wiki/.local



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Document Keywords: bonjour, mdns, local, proxy, dns, itunes, cs3, internet, name resolution


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