Rather than manually configuring iptables, save yourself some time and use UFW (the Uncomplicated FireWall) https://help.ubuntu.com/10.04/serverguide/firewall.h

Rather than manually configuring iptables, save yourself some time and use UFW (the Uncomplicated FireWall) https://help.ubuntu.com/10.04/serverguide/firewall.html https://help.ubuntu.com/10.04/serverguide/firewall.html which is far easier and just as secure (and reduces the risk of misconfiguration).