Many people might not have gauged the power of IPTABLES!
One of the nice features is that you can use it to limit the bandwidth of outbound traffic going through this firewall. (Say you have a windows network and this Linux machine is the gateway and you want to limit bandwidth of a particular machine using iptables.)
You will realise that most software firewalls like Untangle or Smoothwall don't provide the feature of bandwidth quota control in their open source versions. So fear not, heres the way to go!
To limit Bandwidth Quota (The below example will allot within 2GB max usage):
iptables -I FORWARD 5 -s <SOURCEIP> -p tcp -m quota –quota 2147483648 -j ACCEPT
iptables -I FORWARD 6 -s <SOURCEIP> -j DROP