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Is it possible to run a full router on Xen's dom0 between a real (physical) LAN and the Internet, with ocasional domU's booting up as I need them?

What problems should I be aware of?

Any particular tips?

Is there any big performance hit, if the processor doesn't support hardware virtualization? (just for the dom0, not for domU's, which won't stay up for long anyway).

I want to have it "just in case". I know I will need the virtual instances, and when I need them, I want to create them as hassle-free as possible, without having to reboot the router every time.

Thanks.

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The best practice is to have a hypervisor be just a hypervisor, but I don't see any problems turning it in the router.

But I would recommend to set up a virtual router in the DomU, with a paravirtualization you shouldn't face any serious performance problems. Especially when you switch some time to vt-x + vt-d and will be able to passthru a physical network card inside a guest.

We have such virtual routers in the production, running RouterOS on a single Xeon core (even without a direct access to the card) and routing 700-800mbit IPSec without any problems.

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Could you please give more details on the hardware specs of that server? It would be great to have some hands-on data I could relate to. Thanks. – Flavius A Jan 21 '11 at 1:45
usual machines, nothing special. i.e. one router is installed on the single core of E5335 (actually now it's running on a 2 cores), another one on a core of E5420 etc. Supermicro server boards with Intel network cards. Currently we use VMWare ESXi, RouterOS doesn't support Xen (but it runs very well on ESXi & KVM). But I'm sure with Xen it could perform even better (in a comparsion with ESXi/KVM without vt-d). For Xen you may choose Vyatta or make a router from any Linux distro you like. – disserman Jan 21 '11 at 2:09
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actually a couple of months ago we've replaced all physical routers with a virtual ones, except the places where we need more than 1-2 gigabits. They do all everyday tasks: routing, filtering, nat, IPsec, OSPF without any problems. and I guess it's much more reliable then having a physical appliance. The physical routers die very rarely but the virtual will never die :) The modern x86 cores are fast and cheap and in many tasks can perform equal or even beat some network-optimized processor units. – disserman Jan 21 '11 at 2:12
Thanks for your help! – Flavius A Jan 21 '11 at 2:33
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