"Install Xen 4.0 and Libvirt like on F12 (  ). Via
my experience xend will hang for 5-7 min at startup and xen managed
bridging will fail as well. This behavior stays the same under
either 188.8.131.52 or 184.108.40.206 pvops kernels. At the same time PV
guests might be unable to obtain IP via interface virbr0. Ubuntu
Lucid official xenified installer fails with DHCP request been sent
to virbr0 under either 220.127.116.11 or 18.104.22.168 kernels,unless you
will manually place Lucid guest on subnet 192.168.122.0 and point
to DNS Server of your's ISP. In this case installer will continue
fetching data from Internet and been created Lucid PV DomU would be
routed to the Net via bridge virbr0 , having static IP address.
Virt-install of F13 PV DomU does detect virbr0 with 22.214.171.124 and
fails to do that with 126.96.36.199. Workaround for the issue follows
bellow. There are no any problems with HVM DomUs with any dhcp
bridge either virbr0 or br0 created manually.
"In general, independent DHCP bridge is required , in particular
for Ubuntu Lucid PV install. On the other hand F13 PV DomU
virt-install behaves different under different kernel"