same MAC, same IP, different interface - NAT possible?

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I have a setup* in which I have a server with multiple virtual network interfaces (vif1 .. vifX) that are connected (bridged) to one virtual machine each (vm1 .. vmX) which all have the same IP and MAC (let's say 192.168.1.100 resp. 00:11:22:33:44:55). In addition to that my server also has one regular network interface (eth0) connected to the rest of my network (10.0.0.0/16).

Now I would like to be able to provide NAT-like capabilities such that every packet coming from vm1 reaches the regular network as coming from 10.0.1.1, every packet coming from vm2 as 10.0.1.2 and so on. Of course, packets coming from the network destined towards 10.0.1.x should also be correctly translated by the server such that vmX will receive them.

From what I understand I could use ebtables with the snat-target to rewrite the MAC addresses for the vifX bridges, such that the remaining network would see at least a different MAC address per VM. However, I cannot see an easy solution to rewrite the IP. Using iptables nat-table and the snat-target will not work, since I would need to also filter on the source-mac or incoming device, but the snat-target is only available on the POSTROUTING chain.

One possible to solution would be to write a small program that listens on a rawsocket on every interface, rewrites packets and re-sends them on the correct interface, but I'd rather avoid that and use standard tools instead.

I would be very grateful for ideas/tips,

posted Jan 3, 2017 by anonymous

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