I have a setup, where TP-Link Archer C6 as my primary router and D-Link 2750U router as secondary router. The secondary router is connected to primary using Ethernet cable (Due to they being far apart). And I use my secondary router's wireless network to connect devices. In short, my secondary router is acting as a wireless Access Point. Secondary has DHCP server off. Now if I want to check which devices are connected to my secondary, I login to my Primary router's admin panel. Its is TP-Link router. So I go to Advanced menu and click on status. It gives me a complete list of details. In that, there is one detail with heading "Wired Clients". As my secondary router is connected to primary using ethernet cable, the devices under "Wired client" heading are the devices that are connected to my secondary router. Also, I can find all the names of all devices, directly or indirectly connected to my primary router, in DHCP client list of primary router's admin panel. It can be found under Advance menu, somewhere in Network tab. Now, I tried finding details (IP and Mac address) of secondary router on primary router's admin panel, but i couldn't find any. There may be ways to find such details using some Operating system tool or any third party tool, which I am currently unaware of. I will try finding the solution and create a video on it. Thanks.

This problem occurs after setting router to repeater mode

@@professorr_writes I did face the same issue (in repeater mode), I tried upgrading and downgradig the router's firmware. But none of them worked permanently for long time. It was weird because it sometimes worked and sometimes didn't. Then after lots of searching, I found the stock firmware (but from non dlink website). I flashed that firmware in my router and since then its not giving me this issue. Otherwise I had to reload the configuration file to my router quiet often. You may try the same, but with firmware from official website. If I remember right, 1.06 is the latest one. You check your router's hardware version and then download the appropriate firmware.

​@@tinytips4823bro mine also dir 816 there os no option of repeater plz help

When you log in to your router settings, under the Wireless 5G tab, you can find "Enable SSID Broadcast". The checkbox next to it has to be check-marked (enabled). This will enable your 5G SSID for the repeater. Now you should be able to see both 2.4GHz and 5GHz band networks.

If the router does not have the repeater setting mode then the firmware is not supporting it. Make sure to update the router's firmware to the latest one.