Definition
Port forwarding (in the VPN context) is a feature where the VPN provider opens a specific public port on the VPN server's IP and forwards any traffic arriving on it back through the tunnel to a port on the user's device. Without port forwarding, NAT blocks all unsolicited inbound connections — fine for ordinary outbound browsing, but a problem for any application that needs to receive direct connections.
Why It Matters
BitTorrent users need port forwarding to seed efficiently — without it, they can only connect to peers who have an open port themselves, which dramatically reduces the swarm they can interact with. Hosting a game server, running a self-hosted application, or accepting inbound connections to any service all require port forwarding. Some VPN users also want a stable inbound endpoint for remote SSH or remote desktop while keeping their home IP hidden.
Provider Support
Port forwarding is increasingly rare among consumer VPNs because it has been used for abuse — running services that attract DMCA complaints or law enforcement attention. Several major providers have removed it; others (Mullvad until 2023, AirVPN, ProtonVPN with paid plans, IVPN) still offer it. Where offered, it typically requires manually requesting a port number per session or holding a paid 'static port' for persistence.