VMWare Fusion XP VM Losing DNS !

October 25, 2008

I’ve been running OSX Vmware Fusion 1.x and XP SP2 & SP3 for over a year and it’s been ROCK SOLID ! I run a web-connected OSX host, and a XP VM VPN’d into a corporate network all day, every day and I have not had a single problem. Until this week…when my calm seas were interrupted…

Out of the blue I notice witin the XP SP3 VM was failing to resolve DNS queries. OK. Why? I basically ran a number of diagonstics, checked driver versions and everything checked out in terms of VM integrity.No idea. The worst kind of problem…

I checked out the net and located numerous threads deliberating over the XP “Unable to flush DNS cache” type of errors, with long and elaborate threads falling into the detail of comparing router firmware versions and other such infinate variables. Eject..Eject…

It was only when I ran the VMWare packet sniffer on the OSX host I could see that the XP VM was requesting DNS, and the resoponses from the OSX host were being dispatched. From my understanding of low level IP it appeared that all was performing as expected. However I then started thinking about reasons why UDP packets were being neglected by the XP VM’s IP stack….BINGO !

I then checked out the Windows XP Event Viewer under the Security event list, and there I see all my DNS responses (from the OS X host) arriving back at my XP VM as UDP packets, all being summarily discarded by my failed/corrupted firewall. Couple of minutes later, having run the ‘support’ utility from the firewall supplier, the flood-gates openend and UDP/DNS was back in business.

Symptoms I encountered in XP:

  1. DNS resolution (i.e. ping http://www.xyz.com) within XP VM failing but direct direct addressing worked ok (i.e. ping 123.123.123.123)
  2. nslookup in the console returned ‘no response from server’ errors in response to queries.
  3. Right-clicking on the network connection icon in XP, and executing Repair proceeded through all steps apart from the final DNS cache at which point Unable to repair connection was returned.
  4. ipconfig /registerdns failed with a non-specific error

In hindsight the symptoms all point to UDP return-path and firewall but verifying the request path with the OSX VMWare vmnet-sniffer utility (located in /Library/Application Support/VMWare Fusion folder) made this a whole lot simpler.


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