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.
Best Answer
Many people don't realise that a consumer "Router" is usually a number of components smushed into a single box.
The WAN / external ports are typically set to 'auto configure' using DHCP... that is they will ask for an IP address, and then use it. Many people don't care what the external IP is, so long as things work.
Hopefully this diagram will help to clarify some points, and hopefully I've drawn it correctly from your description:
IP
stacks will typically have a distinct IP address... thus each router will have an 'internal' and an 'external' IP.IP
stack will have an IP address assigned by your ISP. Don't even try to configure it yourself.IP
stack will have a private address - typically192.168.0.0/24
or similar by default. You are free to configure this.IP
stack will follow on in a similar vein to the Blue... it will likely request an address from the service provider (in this case, Router 1).As a side note, the "Router 2" block in the diagram above is often marketed as a "Cable Router", as many cable providers will supply their own external cable modem. This is just a marketing term, and it is of course possible to use such a router in this configuration, with an external DSL modem, etc...
Equally, it is possible to purchase a "Router" that contains a DSL modem, or a Cable modem built-in (as per "Router 1" above).