Moved softether machine no longer works

[douggoens]

I have a remote client who moved from a comcast environment to an ATT fiber environment.

I was using port forwarding on comcast to allow connection to the VPN machine.
Using the NAT/Gaming to forward the same ports, I cannot connect to the VPN

I'm not really sure where to start
Can someone point me in the right direction? I'm confused as to why it worked in the comcast environment and not now.

[solo]

Note: If your IP address starts with a 10.x.x.x, please visit AT&T’s Port Forwarding Tool to request, view, and remove your Port Forwarding assignments, as well as automatically configure your local AT&T-provided modem/gateway with the touch of a button.

If not, try to disable IPv6, or in passthrough mode and another router, finally contact AT&T support.

[douggoens]

It started with that subnet when it was on Comcast, but I successfully have changed everything over to a 192.168.1.x format. What happens is it tells me that the L2 TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer. This is the exact same set up with the exception of the IP address subnets changing and now it won’t connect.

[solo]

No, it's about CGNAT not your LAN subnet, so check if the router shows WAN IP as 10.x.x.x. Initially test connectivity with SoftEther client not L2TP.