Explanation/Reference:
Explanation:
Configure Name Resolution for a Federation Server Proxy in a DNS Zone That Serves Only the PerimeterNetwork So that name resolution can work successfully for a federation server in an Active Directory Federation Services (AD FS) scenario in which one or more Domain Name System (DNS) zones serve only the perimeter network, the following tasks must be completed:
The hosts file on the federation server proxy must be updated to add the IP address of a federation

server.
DNS in the perimeter network must be configured to resolve all client requests for the AD FS host name

to the federation server proxy. To do this, you add a host (A) resource record to perimeter DNS for the federation server proxy.
References:
https://technet.microsoft.com/en-us/library/dd807045.aspx