Definition
Port forwarding is a router configuration that tells your network to deliver unsolicited inbound traffic arriving on a particular port to a specific device on your local network. It is the standard way to make a self-hosted service, such as a Bitcoin node accepting peers on port 8333, reachable from the wider internet despite the barrier that address translation normally imposes.
How a forwarding rule works
You create a rule in the router's admin interface that maps an external port to an internal IP address and port. When a packet arrives on that external port, the router rewrites its destination to the chosen internal device instead of dropping it. Because the rule is tied to a fixed internal address, the target device usually needs a static local IP or a DHCP reservation so the rule does not silently break when addresses shuffle.
Common uses and pitfalls
Node operators forward port 8333 so other Bitcoin peers can connect inbound, improving the network's connectivity and their own. Others forward ports for a Lightning node, a personal VPN endpoint, or a self-hosted dashboard. The chief pitfall is exposure: any forwarded port is a door the whole internet can knock on, so each exposed service should be hardened and ideally placed behind authentication or a tunnel.
When forwarding is not possible
If your ISP uses carrier-grade NAT you cannot forward ports at all, because the public-facing router is not yours. In that case an outbound tunnel or onion service is the path to reachability.
Port forwarding directly addresses the inbound limitation described under Network Address Translation (NAT); for setups where forwarding is blocked, see Tor.
In Simple Terms
Port forwarding is a router configuration that tells your network to deliver unsolicited inbound traffic arriving on a particular port to a specific device on…