UFW and WireGuard: the tunnel is up and nothing goes through

The tunnel comes up. wg show prints a recent handshake. The client has its address inside the tunnel. And not a single byte reaches the internet. Almost every guide answers this with "open UDP 51820 in the firewall". You already did that — it is why the handshake works at all. The problem is somewhere else, and UFW makes the distinction easy to miss: Entering a machine and traversing it are two different permissions. ufw allow 51820/udp lets packets arrive at the server. Your clients' traffic does not stop there — it goes through the box and out the public interface. That path lives in the FORWARD chain, which UFW denies by default and which no allow rule touches. The four things to check, in order 1. IP forwarding — and the file that overwrites the other file This is the one that costs hours, because the setting looks done. UFW loads its own sysctl file at startup, and it takes precedence over the system one. A value you carefully set in /etc/sysctl.conf can be silently overwritten on the next ufw enable . The right place is /etc/ufw/sysctl.conf : net / ipv4 / ip_forward = 1 net / ipv6 / conf / default / forwarding = 1 net / ipv6 / conf / all / forwarding = 1 Then check the effective value, not the file you just edited: sysctl net.ipv4.ip_forward 2. Forwarding, which is not the same as ingress Targeted, and the one to prefer: sudo ufw route allow in on wg0 out on eth0 Or globally, in /etc/default/ufw : DEFAULT_FORWARD_POLICY = "ACCEPT" The second opens forwarding for every interface. It is a good ten-second diagnostic and a poor permanent configuration. 3. NAT, which UFW never adds on its own Without it, packets leave carrying their tunnel address, which nothing on the internet knows how to answer. In /etc/ufw/before.rules , at the very top , before the *filter line: *nat :POSTROUTING ACCEPT [0:0] -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE COMMIT Two classic mistakes here: putting this block after *filter (it is then ignored), and copying eth0 without chec