Nat – Port forwarding to SonicWALL TZ300 behind router for GVC VPN access

I did something similar recently, where I set up a VPN originating from a Linksys RV082 from behind a NAT router, so it's definitely possible.

Here are a few suggestions to consider:

• Ensure that NAT traversal (NAT-T) is enabled on the Peplink device
• If the Peplink devices supports IPsec, consider using that instead of the RV082
• Check that one VPN endpoint has keepalive enabled, or try sending traffic down the tunnel to bring up the security association
• You probably need to use the WAN port on VPN A to connect it to the LAN behind Router A. Normally, these devices will only listen establish VPN connections using their outside interface.
• If NAT-T is working properly, you don't need to do any port forwarding or NAT mapping on Router A. Try turning off your one-to-one mapping.
• You can get away with only one side of an IPsec security association being configured with a remote peer address. Try setting up VPN a with the remote address for Router B, then configure the security association on Router B to use 0.0.0.0 as the remote peer. It will just listen for a connection that way.

If it still doesn't work, check your logs on both sides, and verify that the Phase 1 and Phase 2 proposals are all using identical parameters.

I'm not familiar with the NSA-series, but the article you followed was instructions how to get two subnets to talk behind ONE physical interface. You're setup is two physically separate LAN ports. It seems like setting up a static route on both SonicWalls should allow them to communicate.