Second IP(local) on WAN interface?

[STDD]

I need to connect to AP before the WAN from lan subnet (Need to monitor two WiFi APs in bridge mode). Each AP have local IP. WAN interface have local IP. Need to add second IP on the WAN interface and something else, but how and what? Can anybody help me?

[malcifra]

Click "firewall" then click virtual IPs. Add your second IP there. Dont forget to add rules under NAT if you want to do forwards and stuff.