The Siphon Project is a portable passive network mapping suite. In the latest public version, Siphon passively maps TCP ports and performs passive operating system detection. This is the first ebuild I've submitted. It's a little awkward, but I think it should do the trick. Siphon is a useful tool for monitoring a network.
Created attachment 12767 [details] net-analyzer/siphon/siphon-666.ebuild
in cvs, cheers.