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Firewall Configuration

Rules that should be added to your machine's firewall
Keep 8545 (or 8000-9000) closed except for the trusted machines - this is the JSON RPC port which gives admin access to the node.
Keep TCP 30303 (or 30300-30400) open for the outside world so other nodes can connect to your node.
Keep UDP 30303 (or 30300-30400) open for the outside world so other nodes can discover your node.