Do you mean Xen, or XenServer?

If XenServer, check out https://www.citrix.com/blogs/2015/10/... which gives a guide for using Mirantis OpenStack.

Many of those networks _do_ have to be isolated though - so if you want a setup with only one NIC and no access to VLANs then also check out https://www.citrix.com/blogs/2015/10/... which explains how you can use GRE tunnels to create fake networks for proof of concept environments.

To be honest i haven't setup openstack on top of xen , but my knowledge says you need to set up OpenVSwitch bridge and set br-ex as the ethernet interface.

You can create openstack with one interface also. Though it does not make any practical sense but I myself made such kind of setup just for development environment. I used devstack in ubuntu and packstack in Centos for it.

If you want more customization then you can always go for a manual installation guide. Here is the link :- http://docs.openstack.org/juno/instal...

If you follow this guide the only thing you have to do it install all the packages that come on the single node. Configuration is exactly the same . It will also take very less time if you install in manually.