You may have lost the configuration file inside the router, maybe a hardware RESET will help.:)

Port VLAN is very simple, all it do is to block the communication between different port VLAN. So if you don't want the client from different AP to communicate with each other, just connect these two...

well, that's weird. Bandwidth control and virtual server are two totally different functions. virtual server do the port forwarding while bandwidth control operate on the bandwidth.

I am not very clear about your demand. maybe you have to configure your ADSL router to be in bridge mode. er6120 support many connection types at its WAN side, including static ip, dynamic ip, PPPoE...

you mean you can't change your router into 4 WAN mode? mine works fine~

change the value of IP release time, change it smaller