Transparent Cache
--> BIG IP DNS Uses External DNS Servers to find the responses to the DNS Queries of a given FQDN or IP address in this method.
--> For the first DNS Query which is hitting on the F5 DNS from the client will be resolved using the pool of DNS Servers configured under the Listener.
--> Once the BIG IP DNS receives the response from the External DNS Server then it caches this response in the memory.
--> Whatever the DNS Queries coming for the same FQDN on the BIG IP DNS will check the cache and if it is available then accelerates the DNS Resolution.
--> As all the DNS Work is done by External DNS Servers configured under the Listener that's why it is called Transparent Cache.
--> If you can see in the below image for the first client DNS Query Request to the F5 DNS, The query is sent to the External DNS Servers, and response is stored in the Transparent Cache.
--> When the second client DNS Query request comes to the F5 DNS then the response is provided directly from the Transparent Cache which provides accelerated DNS resolution.
Resolver Cache
--> In the case of the Resolver Cache Method, the BIG IP DNS itself will perform DNS recursive lookups to the multiple DNS Servers in order to find the DNS response.
--> For the first DNS Query which is hitting on the F5 DNS will be resolved by sending recursive queries to the multiple DNS Servers to get the response.
--> Once the BIG IP DNS receives the response from the Authorative DNS Server for the mentioned FQDN or IP address then it caches this response in the memory.
--> Whatever the DNS Queries coming for the same FQDN on the BIG IP DNS will check the cache and if it is available then accelerates the DNS Resolution.
--> As all the DNS Work is done by F5 DNS Server that's why it is called Resolver Cache.
--> If you can see in the below image for the first client DNS Query Request to the F5 DNS, The query is sent to the multiple DNS Servers and response is stored in the Resolver Cache.
--> When the second client DNS Query request comes to the F5 DNS then the response is provided directly from the Resolver Cache which provides accelerated DNS resolution.
Reference: F5.COM
MD.Kareemoddin,
CCIe #54759
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