I'll just put this here since it didn't appear early enough in Google searches. The iptables firewall is a part of the kernel and not a service, so you can't really systemctl stop it. The solutions I saw others post were about saving the entire iptables state, flushing the tables and then restoring the state when you are done. Not really convenient.
What you can do, however, to prevent iptables from blocking e.g. incoming connections, is
$ iptables -I INPUT 1 -j ACCEPT
Iptables is now in effect disabled for incoming traffic, since it accepts
everything in the
INPUT chain. Then when you have done whatever
you were going to, you can
$ iptables -D INPUT 1
which removes the rule above. Obviously change
something else if there's another chain you want to disable.