I got a 5G gateway from T-Mobile and it doesn't support bridge mode over its LAN ports. So I connected the LAN port from the 5g device to the WAN port of my Routerboard. The 5g gateway is 192.168.12.0/24 and the routerboard is 192.168.10.0/24

I'm having some issues:
1 - DHCP requests/responses are crossing over the WAN port and I'm getting LAN ips from the 5g gateway to the devices behind the Routerboard.
2- I'm not able to get any 192.168.12.x IP on the WAN port of Routerboard from the DHCP server of the 5g gateway.
3- I'm not able to issue DNS requests for any static dns server requests to the Routerboard.

Please help, thanks

Please post a copy of your router's configuration file.

Do an internet search for “mikrotik export configuration”. An example website result:

https://academy.socialwifi.com/hardware ... tik-device

The config file is just text so you can edit it to remove anything you don’t want made public, then copy and paste the text here.

Or follow these step by step instructions:
viewtopic.php?t=203686#p1051720