How can I get the current network traffic broken down by subnet

view story

http://askubuntu.com – I'm trying to modify one of my extensions that shows network traffic from my computer (For an indicator). I'd like to be able to quantify how much of the network traffic I see is coming/going to the internet, and how much is exchanged with my local subnet. Is there any way to make this distinction in Ubuntu using e.g. netstat? (HowTos)