[ubuntu] Ubuntu firewall server in OpenStack

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http://ubuntuforums.org – Hey guys. I'm trying to setup an Ubuntu firewall machine in OpenStack. I've found loads of information on it, such as http://ubuntuforums.org/showthread.php?t=926001, which I followed mostly. However, most places say you need two network cards, which (AFAIK) isn't possible. Well, from some documentation I found, it seems like it is possible but not trivial. I may be wrong. Basically what I would like to do is set up a server that my other OpenStack servers could route the incoming and outgoing traffic, but with only one network card. Could someone suggest a strategy to use - what package, som (Hardware)