Currently, I've got a Centos 5.8 host that I began playing with Xen virtual machines. It's a sandbox sort of server where I try and learn all of this virtualization stuff. In the future, I'll more than likely swith to Centos 6 and kvm, but for now, it's xen.

Searching google and the list, I can't find an explanation of how to add a second virtual NIC to a running VM when I only have one real NIC on the server. For the most part, in my searches it appears that I need a real second NIC on the server to do this. I can find a few examples, but each sort of implies it a one-to-one minimum of real hardware to virtual hardware.

So what I'm asking is "Is it possible to create a xen VM that has two virtual ethernet interfaces on a host that has only one real NIC"? I'd like to simulate a server that I can make a firewall out of and to do that would mean I need an internal and external interface. I'm attempting to create a set of firewalls in a highly available environment to test with. So far, most of the docs I find are for more complex people than I. There's concepts like virtual switches and the like that are creeping into the reading, so the more I read, the more overwhelmed I am.

Did I mention I'm still just starting to explore virtualization? If someone can provide me with a possible yes-no answer and maybe a link to documentation that might explain the way, I'll gladly do all my own grunt work.

Thanks for any and all help.

steve campbell