My system has 6 interfaces, a loopback, a Xen Bridge, and then 4 ethernet interfaces eth0-3. In this system, my DNS server assigned by DHCP on xenbr0 is 192.168.1.1.
Initially eth1 is disabled and DNS assigned (checked via
/etc/resolv.conf) is 192.168.1.1. When I enable eth1, internet on this system stops working, I checked with
/etc/resolv.conf and now DNS is 127.0.0.1 (why?). Anyway DNS resolution doesn't work now.
Question is How can I make internet work while keeping all interfaces active? Why DNS server changes, and how to stop that?
About Environment: This is a Ubuntu 12.04 VM running in Xen in VirtualBox. eth1 is connected to a VBox host-only network 192.168.56.0/24. eth2 and eth3 are connected to VBox internal networks, there is no config on these two interfaces. xenbr0 is xen bridge and eth0 is added as its one port. In Vbox eth0 is sharing IP with host machine via NAT (currently getting 10.0.2.15). IP of host machine is 192.168.1.x and router IP is 192.168.1.1 which is default gateway for host and DNS too. This is hown DNS is propagated upto guest machine via xenbr0.