I'm experimenting with UML for application virtualization. The idea is to have a collection of files - a static UML binary, a launcher script, and a minimal filesystem - that can be used to run a given application in its own filesystem, on most Linux systems.

Right away, a problem: networking on UML is painful!

- TUN/TAP requires creating a new network device for each UML user (or running UML as root). It does work without issue, but the per-user setup makes it undesirable for desktop purposes.

- SLIP likewise requires root access, otherwise I get permissions problems when trying to bring up the interface.

I haven't tried any of the the other options yet, but they don't look a whole lot more promising.

What I'd like is to be able to have something like Xen's NAT functionality - the host gets a static "gateway" IP, the guests each get a static IP, and packets to and from the guests are forwarded via the host. Is this possible, or am I out of luck?

What is UML in this context?

User Mode Linux?

Yes, that would be User Mode Linux, sorry.

Thanks - I am not familiar with that and was trying to imagine how your question related to the Unified Modeling Language...

So now that I understand the questions, I am sorry that I have no useful answer and you must wait for someone else to chime in.