cliffmcp - Thanks for posting your question on the forum!
Based on your configuration, all traffic is being allowed through in both directions without any changes being made. In other words, there is no NAT occurring on your router. When you ping 192.168.1.1 or ping from 192.168.1.1, the 3120 must know how to get to the other subnets in your network. This is why it has a default route pointing to 10.137.8.1. However, the routers in your network must also know how to get back to the 192.168.1.x network.
Could you post the results of a traceroute from 188.8.131.52 to 192.168.1.1 and vice-versa? It would also help to compare this to the results of the successful traceroute from 184.108.40.206 to 10.137.8.20 and vice-versa.
Please do not hesitate to let us know if you have any further questions.
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