wquin1s - Based on your description, it appears the packet is getting lost between "ADTRAN1" and the Zywall. I would probably start by checking the route table on the Zywall. Specifically, you want to make sure that the Zywall has a route for the 10.2.10.x network:
1, Destination Network: 10.2.10.0
Subnet Mask: 255.255.255.0
Next-hop / Gateway: 10.1.10.251
If you are able to ping 10.1.10.251 from Host2, then that tells us that the routing on the Adtran is correct. However, I did notice that the 2 ports on the Zywall (Port2 and Port3) are on the same network. I'm not sure if the Zywall is supposed to be routing between networks or if the ports act as a switch.
I did have a couple of additional questions:
1. Are you able to ping HOST1 from a device that is on the 10.1.10.x network (i.e. ADTRAN1)?
2. Have you tried changing HOST1's default gateway to 10.1.10.251 (ADTRAN1)? If so, what are the results of your ping tests?
It would also be good to view the routing table of the Zywall, ADTRAN1, and ADTRAN2. Please remember to remove any information that may be sensitive to your network.
Please do not hesitate to let us know if you have any questions.
I went ahead and flagged this post as “Assumed Answered.” If any of the responses on this thread assisted you, please mark them as either Correct or Helpful answers with the applicable buttons. This will make them visible and help other members of the community find solutions more easily. If you still need assistance, I would be more than happy to continue working with you on this - just let me know in a reply.