Block external access to office IP adddress

[asifmalik]

We have created a NAT rule to our internal intranet server
I need to allow only 2 or 3 external IP addresses to this over the internet

How do I secure this port to only allow those ips?

[KOM]

A port-forward is a NAT rule plus a firewall rule.  To restrict access to your NAT, simply specify proper sources.  Create an alias and then fill it with the IP addresses you want to allow, then use that alias as the Source on your WAN firewall rule.

[Derelict]

Or use it as the source on your port forward rule and it will automatically propagate to the firewall rule in the default configuration where the firewall rule is created and tracked by the port forward.