To specify that Global Server Load Balancing (GSLB) regions be used to direct traffic to data centers with region-specific content, navigate to the TRAFFIC > GSLB Services page and set the Response Policy to Region Only. When you add a region to a host on the TRAFFIC > GSLB Services page, traffic that originates in that region is directed to the Site IP address.
Several predefined regions are listed on the TRAFFIC > GSLB Settings page. You can also create a custom region on that same page. Scroll down to GSLB Regions and click Add Custom Region. Name the custom region and select one or more small regions from the list. Then click Save. Return to the TRAFFIC > GSLB Services page to specify using the new Custom Region.