Configuring DNS cache global settings

Normally, a resource record obtained via recursive resolution remains cached for the TTL supplied in the query response. On BIG-IP DNS, the TTL may be overridden by the value in the Maximum TTL setting. The BIG-IP system deletes records from cache when the TTL specified in the response is reached or when the Maximum TTL is reached, whichever occurs first.

As mentioned in K14922: Configuring the DNS cache TTL statement for the BIG-IP DNS system, "In certain cases, you might want to change [Maximum TTL] for the BIG-IP system. For example, setting [Maximum TTL]... to a lower value can have one or more of the following benefits:

• It mitigates DNS cache abuse (for example, ghost domains)
• It reduces "bad" records caching (for example, poor hostname migration planning may require you to flush the bad records from the DNS cache)