Xen domainU Guest has an IP address on 192.168.122 subnet instead of the subnet to which the domain0 host belongs

Problem Summary - After booting a Xen domainU it is discovered that the system has been assigned an IP address in the 192.168.122.* address range which is a different to the subnet to which the host (domain0) system belongs. This configuration is commonly encountered on Red Hat Enterprise Linux and recent Fedora releases.

Firstly, it is important to understand that, rather than being a problem, this is the intended behavior for Xen on a number of Linux distributions. The objective is to provide the ability to create a private network of Xen domainU guests protected though Network Address Translation (NAT) on domain0. In fact, all domainU guests on the host in question will be assigned an IP address from this subnet and will be able to communicate with each other, although by default they will be unable to communicate with the outside world.

For many Xen configurations this is desired behavior for which there are a number of benefits. For some configurations, however, an IP address on the same subnet (and issued by the same DHCP server) as the Xen host system is needed.

Solution - By default a number of systems (typically Red Hat based distributions) default to using the virbr0 network bridge for the domainU guests. This provide the private network.