We have Vigor 2860 with 2 x AP900 attached on LAN ports directly connected to that device. I essentially just want the 2860 to act as a wireless controller as we have another L3 device in the network connected to a firewall. I'm thinking I should have the WAN2 port plugged into the rest of my LAN, with that port setup with "Enable bridge mode" and to Bridge "LAN 1", with my APs connected to the other ports on the 2860.

Assuming I'm correct on the above with the use of bridge mode on the WAN2 port and bridging to LAN 1, I'm now confusing myself on management of the 2860. I see following options

1. I put an IP address on the WAN port on the same subnet as the rest of my network with a default gateway of my L3 device and have no address on the LAN1 interface (is this possible?)
2. I put an IP address on the WAN port on the same subnet as the rest of my network with a default gateway of my L3 device and also have an IP address setup on LAN 1 on the same subnet.

Or am I totally wrong?

TIA