firewall – Does port 8333 should be opened as TCP_OUT or TCP_IN?
Port 8333 is just related for inbound connections. Opening it permits different nodes to start out speaking along with your node.
That mentioned, a Bitcoin node can totally take part within the community even for those who do not enable inbound connections (to port 8333). It’s going to use outgoing connections, which begin from random increased unprivileged ports and connect with port 8333 of one other node. If you happen to can enable incoming connections that is good for the well being of the Bitcoin community, in any other case outbound connections are functionally equal.
Bitcoin Core may supply a JSON-RPC interface on port 8332, so for those who want that, act accordingly.