I have just installed a fresh Ubuntu 12.04 on my server. Previously I was using 10.04 (which worked fine), but had a disk crash (on the Root/OS disk), and had ni usable backup.
I have installed KVM, and have been trying to get my virtual machines to work. I mainly use 2 VMs: one running Ubuntu 9.04, for web, database, and LDAP services, and one running Windows-XP (for MS-Office).
The VMs will both start, but network access is not working. Neither VM is getting an IP address assigned via DHCP from my Internet modem. Assigning static IP addresses doesn't help much; I can't reach any network resource beyond the host, and port forwarding (set up on the Internet modem) is not working.
I am using bridged networking for my VMs, so that they can be accessed by external systems. I created a bridge (br0). The host gets an IP address via DHCP, and has working network access. This is the output from the 'brctl show br0' command:
In this output, tap0 is the Ubuntu 9.04 VM, and tap1 is the XP VM.
bridge name bridge id STP enabled interfaces
br0 8000.0019b91573b5 no eth0
This is my host's interfaces file, which was fine with Ubuntu 10.04:
This is the output from the 'route' command on the host:
iface lo inet loopback
iface eth0 inet manual
iface br0 inet dhcp
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default 192.168.0.1 0.0.0.0 UG 100 0 0 br0
link-local * 255.255.0.0 U 1000 0 0 br0
192.168.0.0 * 255.255.255.0 U 0 0 0 br0