What is this strange network access through the IPTV port in the provider's router?

Question

iptables

Hello. About 5 years ago I connected to the Internet with IPTV. The provider gave an optical terminal and a TV box. The Internet goes through three ports out of four, but the fourth one is magical for boxing.

The other day I found a TV box emulator and it became curious to use it on a laptop. The stalker portal is prescribed there, the poppy address of the TV box and everything is ready.

I took the laptop, turned off the box and connected the laptop instead. I start the emulator and it gave an error connecting to the portal. I look at the status of the network, and it writes an unidentified network. I turned on the box with the cable disconnected so that the portal would not load and it would give out the settings (this is how I found out the portal address). I cut the cable into the magic port and it gave out IP 10.15.XXX.XXX, cut it into a regular port. IP 192.168.100.10, that is, the standard local address of the Huawei router.

The question is, what could they do there? And how can you set up a computer so that it can get into this network and get through to the portal? Tell me please!