I'm trying to understand the assignment of IP addresses when the broadband modem (for example Draytek 130, which in the UK only operates in bridge mode) is separate from the router.
My understanding is that a bridge operates at level 2; it passes packets from one side to the other, converting between the different technologies at levels 2 and 1 (in this case between Ethernet on the inside and some-telephone-stuff (which I don't really understand) on the outside. Therefore it has no IP address
of its own, IP being a level 3 thing.
So if the ISP assigns an IP address to the subscriber of (say) 18.104.22.168, then that's what the WAN port of the router is, and the modem is transparent at the IP level.
But the manual for the Draytek modem says that if you connect a PC to the ethernet port it can get a DHCP address in 192.168.2.x. That's the same ethernet port
that bridges 22.214.171.124 to the WAN port of the router. How can this be? Does the modem run a web server on some 192.168.2.x address at the same time
as bridging the external IP address to the router?
Like this? Have I got that right?
=====broadband==== MODEM ====126.96.36.199=== router
|--- 192.168.2.x ---- PC