Why do you need a second router? And how to get rid of it?

Question

Network administration

When the provider connected to the Internet, he implemented a scheme incomprehensible to me with two routers: an intercom (essentially a simple sip phone) and a second router were plugged into the first one. Actually I wanted to simplify it all to one router. Can you please tell me if this can be done? And how can I find out the ip of the second router?

Answer 1

The first one most likely works in switch mode (and therefore it does not have its own IP), so the intercom and the second router are in the provider's internal network. The second one, in router mode, distributes the Internet to your PC, laptop, smartphones, etc.
You can remove the first one altogether, but then there will be nowhere to connect the intercom so that it is on the 172.* network, and not on your internal 192.168.*
"it works - don't touch it"
:)

Answer 2

Connect the wire from the first router (which goes to the second one) to your computer directly, assign the static address given to you and run wireshark, then study the packets. Perhaps your second router has the address 172.23.238.1. And perhaps the first router raises the tunnel, but in a word - your wire is crooked.