Firewalling in Linux may be deadly. An improper configuration can bring the network to its knees. One command that may save your day is
netconf --resetfw
This command deactivates all firewalling rules. It does not affect the configuration -- it affects only the working set.
netconf --update
will reactivate the rules. You may need to use those two commands to check out if a network malfunction is caused by your firewalling rules or not.