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 184.108.40.206 to 192.168.1.1 and vice-versa? It would also help to compare this to the results of the successful traceroute from 220.127.116.11 to 10.137.8.20 and vice-versa.
Please do not hesitate to let us know if you have any further questions.
I went ahead and flagged the "Correct Answer" on this post to make it more visible and help other members of the community find solutions more easily. If you don't feel like the answer I marked was correct, feel free to come back to this post to unmark it and select another in its place with the applicable buttons. If you have any additional information on this that others may benefit from, please come back to this post to provide an update. If you still need assistance, we would be more than happy to continue working with you on this - just let us know in a reply.