No, they don't. I have configued a firewall rule to disable direct TCP/IP packets / communication.

I did test it - if pingable, then Skype uses direct P2P without any traffic on my Internet line. Although I want traffic to stay local, my security should be really tightenend. I don't want all subnets to see eachother.

All developers are on same subnet and can see eachother. Marketing works on another subnet ; Traffic not allowed between them, but I would like to configure my setup to enable Skype to route / proxy the traffic