NAT traversal lets two computers behind their respective NATs establish a secure VPN connection with each other without using a relay. Many believe you need a service (such as ourselves) to do NAT traversal. In truth, any WireGuard peer sitting behind a traditional NAT can easily be accessed using the hole-punch technique.
This technique may not be applicable for coffee house road warriors, but if you have two relatively stable external IP addresses for the machines, you can simply configure WireGuard correctly, set PersistentKeepAlive to 5, and viola, you’ve defeated the NATs. Consider yourself a true professional the first time you do it. It does not require port forwarding, nor does it require UPnP. But it does require a “traditional” NAT, and not a carrier-grade NAT.
Hole Punch Technique
The hole-punch technique lets WireGuard peers with relatively stable IP addresses connect through their respective NATs. Wireguard is a UDP-based protocol, similar to DNS. So to illustrate, we will use DNS as an example.
If one does a DNS query like this:
C:\Users\nettica>nslookup google.com 8.8.8.8
Server: dns.google
Address: 8.8.8.8
Non-authoritative answer:
Name: google.com
Addresses: 2607:f8b0:400a:80b::XXXX
142.250.69.XXXProgrammatically what is happening with your computer and your NAT is this:
- Your UDP packet is sent from 192.168.2.2:12345 to port 8.8.8.8:53 (DNS) with a query for google.com
- 8.8.8.8:53 replies with the answer you see above
In reality, the UDP packet is sent to 192.168.2.1, your default gateway. The NAT on this gateway translates the address from 192.168.2.2:12345 to 172.16.45.23:12345 and then sends it to 8.8.8.8:53. The reply goes to 172.16.45.23:12345. The NAT sees it recently sent a packet to that address, so it forwards the reply to 192.168.2.2:12345. Note that the NAT translates the network address, but not the port.
This is how and why you can defeat the NATs. Simply knowing each other’s IP addresses (and ports), and then persistently pinging them with a keepalive will cause the request of one machine to look like a reply to the other, allowing WireGuard to synchronize the connection. It is safe and secure. Only the addresses you are actively pinging can connect through the NAT. WireGuard secures the connection and everything sent over it.
Pro Tip:
Use the same port number on both sides of the connection to simplify the process. You can use the WireGuard port 51820, or, a nice round number like 50000.
Multiple Machines Behind a NAT
To communicate with multiple machines behind the same NAT, you must use unique ports for each machine. While most NATs do use tuples to map who is talking to whom, they can get confused if two machines using the same port are talking to the same remote machine (over UDP). Trust us when we say this tip will save you hours of debugging.
Relay Service
If the above doesn’t solve your problem, then take a look at our Relay Services. We provide high-performance bandwidth, so you’re not stuck with mediocre performance.
More Information
Setting Up Nettica Tunnel and Relay Services