Explanation
https://docs.microsoft.com/en-us/windows-server/networking/dns/deploy/primary-secondary-geo-location Geo-Location Based Traffic Management.You can use DNS Policy to allow primary and secondary DNS servers to respond to DNS client queries based on the geographical location of both the client and the resource to which the client is attempting to connect, providing the client with the IP address of the closest resource.In the Internet infrastructure, however, the DNS servers are widely deployed in a primary-secondary model, where the writable copy of a zone is stored on selectand secure primary servers, and read-only copies of the zone are kept on multiple secondary servers.The secondary servers use the zone transfer protocols Authoritative Transfer (AXFR) and Incremental Zone Transfer (IXFR) to request and receive zone updatesthat include new changes to the zones on the primary DNS servers.
Following is an example of how you can use DNS policy in a primary-secondary deployment to achieve traffic redirection on the basis of the physical location of theclient that performs a DNS query.This example uses two fictional companies - Contoso Cloud Services, which provides web and domain hosting solutions; and Woodgrove Food Services, whichprovides food delivery services in multiple cities across the globe, and which has a Web site named woodgrove.com.To ensure that woodgrove.com customers get a responsive experience from their website, Woodgrove wants European clients directed to the European datacenterand American clients directed to the U.S. datacenter. Customers located elsewhere in the world can be directed to either of the datacenters.Contoso Cloud Services has two datacenters, one in the U.S. and another in Europe, upon which Contoso hosts its food ordering portal for woodgrove.com.The Contoso DNS deployment includes two secondary servers: SecondaryServer1, with the IP address 10.0.0.2; and SecondaryServer2, with the IP address10.0.0.3. These secondary servers are acting as name servers in the two different regions, with SecondaryServer1 located in Europe and SecondaryServer2located in the U.S.There is a primary writable zone copy on PrimaryServer (IP address 10.0.0.1), where the zone changes are made. With regular zone transfers to the secondaryservers, the secondary servers are always up to date with any new changes to the zone on the PrimaryServer.The following illustration depicts this scenario.