I have a D-Link DSL-2520U ADSL modem router and a Netgear WNDR3700v2 router. I want to use the DSL-2520U as ADSL modem only, and the WNDR3700 for NAT, firewall, DHCP and wireless access.
How I should setup the DSL-2520U to act as modem only? In particular, I don't understand the ADSL configuration required.
Details
The DSL-2520U is an ADSL modem router, with a single ethernet port and no wireless capability. It does have NAT, firewall, DHCP, and more things that I dont' need. For reference, I've put its help pages here and here.
I have OpenWRT installed on the Netgear WNDR3700 router. In my current setup, the DSL-2520U does NAT and firewall. The Netgear router has its firewall and NAT disabled (to avoid double-NAT). It does wireless and DHCP.
I want to change this setup such that the DSL-2520U only acts as the ADSL modem. I want the Netgear router to take over the NAT and firewall responsibilities, so that it can then be setup with pretty-much the default OpenWRT configuration. In addition, I still want to be able to access the DSL-2520U admin page.
Edit:
I'm happy to go without access to the DSL-2520U admin page if that allows for a better setup.
21 Answer
Whatever you do to get your Netgear router to handle the connection directly will prevent you from accessing its configuration page. There is absolutely no way to overcome that limitation which you impose on yourself.
Your best solution to keep access to the modem-router's configuration page would be to enable DMZ from the modem-router pointing to your Netgear router. This would give you all the routing and firewall flexibility you could need on the Netgear router.
Update based on question update: If you do not need access to the modem-router's configuration page, the best solution to give full control to your Netgear router is to put the modem-router in bridge mode (which is present and documented in its manual).
Refer to your modem-router's manual for reference.
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