How to Improve P2P NAT Traversal Success

Before you begin

1. Find the p2pRemote device's IPv4 address and default gateway in the operating-system network settings.
2. Open the default gateway in a browser and sign in to the router.
3. Create a DHCP reservation for the device so its address does not change.

Step 1: Enable UPnP

1. Find UPnP under Advanced, NAT Forwarding, or Port Mapping and enable it.
2. Save the setting and restart the router if requested.
3. Restart p2pRemote and retry the connection.
4. If it succeeds, keep UPnP enabled and do not configure DMZ.

Note: UPnP is preferred because applications request only the mappings they need. Enable it only on a trusted home network.

Step 2: Test with DMZ or Exposed Host

1. Find DMZ Host or Exposed Host under NAT Forwarding.
2. Enter the reserved IPv4 address of the device running p2pRemote and save.
3. Keep the operating-system firewall enabled, restart p2pRemote, and retry.
4. If the test succeeds, router filtering was the likely cause. Disable DMZ after diagnosis unless it is truly required.

Note: DMZ forwards otherwise unmatched inbound traffic to one device and has more risk than UPnP. Keep the device patched and its firewall enabled.

Handle double NAT and CGNAT

1. If the router WAN address is private, the modem or ISP adds another NAT layer.
2. Prefer bridge mode on the modem. As a temporary alternative, make the main router's WAN address the modem's DMZ host and enable UPnP on the main router.
3. For ISP CGNAT, router settings cannot control the outer layer; ask the ISP for a public IPv4 address.

Verify in this order

• Test with UPnP only first.
• Use DMZ only if UPnP still fails.
• When both endpoints have symmetric NAT, improve at least one endpoint and preferably check both.
• If it still fails, compare with a mobile hotspot and record both NAT types, WAN addresses, router layers, and failure time.