pfSense is a FreeBSD-based firewall inspired by m0n0wall and after a quick trial run, it looks very nice. I just tried the VMWare virtual machine for it and was very impressed. I think I'll stick to m0n0wall for the front lines, but then use pfsense for behind the scenes routing and load balancing.
I doubt I'll continue to use VMWare, but it is convenient right now. I'd like to be able to understand the networking stack used with QEMU and the vde. Just did a quick search and this turned up:
http://alien.slackbook.org/dokuwiki/doku.php?id=slackware:vde
Looks to be exactly what I'm looking for! Its good reading, but I found a typo and I can't fix it, presumably because their wiki has been spammed too many times:
The drawback of user-mode networking is that is is
Should be "it is". Oh well. No big deal.