Host labels enable you to create logical groupings of hostnames with similar configuration characteristics. You can add hostnames or entire subnets to labels. When you use hostnames in host labels (as opposed to subnets), the appliance retrieves from your DNS the IP addresses that correspond to that hostname, and uses those addresses to match the destination IP addresses for a rule using the host label.

Appliances resolve hostnames through your DNS, and they automatically re-resolve hostnames once daily. If any problems arise during the automatic or manual hostname resolution, the summary section of the host labels page quickly alerts you that there’s a problem. Appliances relay changes in IP addresses to rules after resolving them; you don’t need to update labels or rules.

You can manually resolve the hostnames. After you manually resolve the hostnames, appliances schedule the next automatic resolution time to be 24 hours in the future.

You can show or hide resolved IP addresses of the hostnames.

Appliances include a predefined host label, SaaS Application, which detects any IP addresses that carry traffic destined to a cloud, or SaaS, service. As SaaS applications are added or deleted, the host label is automatically updated with the list of associated IP addresses. This host label removes the requirement that domain rules and SaaS acceleration be mutually exclusive. Use this label with an auto discover in-path rule, and set cloud acceleration to auto.