I am implementing some modest iptables on xubuntu 17.04 and came across this blurb from IptablesHowTo Ubuntu
WARNING: Iptables and NetworkManager can conflict. Also if you are concerned enough about security to install a firewall you might not want to trust NetworkManager. Also note NetworkManager and iptables have opposite aims. Iptables aims to keep any questionable network traffic out. NetworkManager aims to keep you connected at all times. Therefore if you want security all the time, run iptables at boot time. If you want security some of the time then NetworkManager might be the right choice.
Later on it goes on to talk about how to run iptables at startup with network manager. Is this prescribing just making sure that network manager runs iptables, using a more controllable manager like wicd, or configuring everything myself, because I'm not keen on the last option. I don't mind doing wired connections myself but my attempts at manually configuring wireless connections so far have been..all I want is for it to use wpa2 and not connect or change connections automatically, and to use the iptables I configure.