I have been using my local ISP which connects 2 TP-Link routers, #1 and #2 don't have DHCP enabled. The gateway for my ISP modem, which is a MitraStar GPT-2741GNAC-N2, is this one:
192.168.15.1
So, I usually disable the 2.4 and 5 GHz networks from the ISP modem, and only use the TP-Links...