So let's assume I connect a secondary router to my first. An Ethernet cable from one of the LAN ports to the secondary router's WAN.
Now, how does my secondary router actual obtain its IP address? Is it through DHCP protocol or any other?
The reason that I ask is that, when my ISP upgraded my 1st router (it's also a modem) firmware, apparently according to them I had to bridge the 2nd router through its LAN interface 4. There's no possibility to assign an IP Address manually to this interface, they started use the concept of "DMZ" somehow misleadingly. However, when I configured the first router to bridge LAN interface 4 like they said – my 2nd router started acting like a switch, even though it was connected through WAN. Although, a DHCP server (Windows Server 2012) connected to the 2nd router works perfectly fine; it receives an IP address from 1st router's DHCP and hands out addresses to its clients.
So perhaps a weird question, but do routers obtain their external addresses differently from DHCP clients? From a theoretical standpoint, routers shouldn't be any different.