Finally, I disabled the routing NAT system on the Verizon Westell 6100G Modem. Thanks to the guide of this site, I managed to bridge the modem to the router. I remember I did attempt such bridging but to no avail. Perhaps it was the slow login connection speed of Verizon's PPPOE.
With the assurance of such site, I waited confidently until success. Now everything from remote access to access restriction are working.