Is the router's DHCP server visible on the WAN?

Question

DHCP

The home Internet began to slow down, in the admin panel of the router I found three dozen wired connections, although all my devices are wireless at home.
After rebooting the router, the number of connections grows to 20-30 within a few tens of seconds, addresses are issued from the pool set on the router.
It is logical to assume that the router distributes IP addresses and allows all neighbors on the network to access the Internet.
My connection diagram:
Optics from the provider -> converter -> Asus RT-N53 (pppoe connection)
I updated the firmware today to the latest - 3.0.0.4.376.3754, the connections still appear seconds after the reboot.
Access from WAN is closed, DynDNS and others are disabled.
Where to dig to stop this disgrace?

Answer 1

Are you sure you plugged the uplink into the WAN port? )