We have block of five IP addresses assigned to us from our ISP. They were routed through an ADSL connection to a Zyxel P-660 router, and we used three of them directly on the second NICs of three servers. The Zyxel quite happily allowed all ports to be directly accessed on these three servers from outside.
Unfortunately this router has died and is "end of line", and we have now been provided with a Linksys X3500 as an alternative by our ISP. I have disabled NAT and turned off the firewall. The servers can all access the internet outbound but no inbound connections are being received from outside.
Anyone got any ideas what the problem might be?