Do I need to configure my firewall to run Bitcoin?

Do I need to configure my firewall to run Bitcoin?

Bitcoin will connect to other nodes, usually on TCP port 8333. You will need to allow outgoing TCP connections to port 8333 if you want to allow your Bitcoin client to connect to many nodes. Testnet uses TCP port 18333 instead of 8333.

If you want to restrict your firewall rules to a few IPs, you can find stable nodes in the fallback nodes list.