I have several VMs set up running on top of Citrix XenServer 6.1 in a lab network, but I think this issue might not be specific to XenServer.
There are several different OSes running:
- Fedora 19
- Ubuntu 12.04 Desktop
- Ubuntu 12.04 Server
- Windows 7
Each one pulls two DNS server addresses from DHCP:
- Primary: 172.16.18.68, which is our local DNS on our lab network. It resolves names inside our lab network.
- Secondary: 10.10.201.11, which is the DNS outside of our lab network but still part of our company. It provides our access to the outside world.
On Windows 7 and Ubuntu 12.04 Server, I can resolve domain names outside and inside my lab network. On Ubuntu 12.04 Desktop and Fedora 19, I can only resolve names inside my lab network -- I can't resolve any outside. I can still visit google.com by typing 184.108.40.206 in the web browser though, so I do have access to the outside world, just not DNS. If I switch the order of the DNS servers though, then I can resolve outside names but not inside names. So Fedora 19 and Ubuntu Desktop are only using the first server in the list of DNS servers, and if that fails they don't try the alternate one. Why is that? And why does the same thing not happen on Ubuntu Server and Windows 7?