You can use iptables for this, something like:
iptables -N tcp_s80
iptables -A OUTPUT -p tcp --sport 80 -j tcp_s80
#and to read data (how many bytes/packets went by your port 80)
iptables -L -v
but every port need own rule, so it can slow down your network if you want to trace many ports. Other method is using "ntop" daemon.