I've set it up as a static IP and activated DHCP and NAT. Now I've set up my modem as a bridge and configured the Airport Extreme to handle everything. NAT and DHCP were done at the modem, but I couldn't get WOL (Wake On LAN) to work (an Apple technote specifies that this setup won't). My previous setting was with the modem configured to connect using static IP and the Airport Extreme as a bridge.
I've recently been assigned a static IP by my ISP provider ().