I connected my router and DSL Router (in bridged mode) together like this:
Strange setup, I know. :) The reason was I wanted my DSL router to continue to work as a switch and WiFi AP, while it's in bridge mode and let router on second floor to handle the rest (traffic control/QoS, port forwarding, and so on). However I'm concerned about the security with this setup. Since the DSL does not provide internet connection in itself, it just handles the digital signal to TX/RX, and only router does connect to the internet through PPPoE. That being said am I exposing my whole network to the internet? By the brief tests I did on my server that's outside my network it looks like my network is protected by router. I couldn't get ping to my internet address after activating "Ignore Ping Packet from WAN Port to Router" on my router.
But I'm not really expert on these things. What should I look for to test my security? And what are your opinions?