From your post#6, it looks like you're doing only port forwarding?
I'm not an expert on this, but if you're trying to map those ip to internal server/system. You can add those ips into VIP as proxy arp and add NAT1:1
Interface:WAN, External IP: x.x.x.179 , Internal IP: 192.168.100.3, Description: Server 1
Interface:WAN, External IP: x.x.x.180 , Internal IP: 192.168.100.4, Description: Server 2