Answer
To restrict the connection only to the employee portal server, the IP address of the application should be added into the list of Trusted IP's.
Step-by-step explanation:
Trusted IP's are the IP's that are used to identify the users that can be verified easily. Those users whose IP's are not listed in the trusted IP list needs to verify their identity by sending them login code on each transaction.
In above mentioned case, We need to enlist the IP address of employee portal list in trusted IP list to ensure the restriction of login to employee only.