Hi,
The best way, is to use some kind of rules on your upstrem border router and not at proxmox level. If you can not do this, and you must use PMX nodes(and is ok for you if you will not block the input, but only the output) then you can do like this:
- install ospf on all of your nodes, and make a simple script who can import your black lists in ospf as a NULL route (only on a single node, and ospf will export to all other nodes)
- even better you can setup fail2ban to also use a null route for bad guys and then ospf will export almost instant this info to rest of the nodes
- the main advantage using this is that route table have cache (firewall do not have this)
- you do not need to import your black list on each proxmox node
- as a general rule, you can use any black-list tool, and import one time for all of your infrastructure
- iptables/firewall will eat more cpu/ram because it will need to process any new connection at least for the same IP
Each variant have pro and con.
Good luck.