How do I make unraid server visible in modem/router + router setup?

[tedlim]

So at home I have a modem/router from my ISP in the basement and another router in the second floor connected to the one in the basement through lan port. Currently my server is connected to the router upstairs and the shares can be seen on any computer connected to this router. However any computers connected to the one in the basement cannot see the server.

 

Can someone explain why this is happening and how I would fix it so all computers (regardless if they are connected to modem/router or the router upstairs) can see the shares in the server?

[JonathanM]

Change the upstairs router to access point mode.