dns cache resolver

A caching resolver is generally doing recursion rather than being an authoritative DNS server.

Delegating domains to your GTM would make it authoritative, so you'd want to configure wide IPs or ZoneRunner records to provide authoritative responses.

Hi Cory, thanks for your response. I will create an widip and delegate my domains to gtmA and gtmB that are placed on different location.when gtmA or gtmB crashed then how dns queries will be redirect to another site? this will being done by gtm ( exmp : gtmA notify to authoritative dns server about gtmB crashed and request redirecting dns queries to itself). or the authoritative dns server monitors both gtms and if one of them is fails then the server redirects queries to available gtm ?

Another question is that normally dns servers load balance queries as round robin. so if want to configure load balance method on the gtm as global availability how this will work? because the auth. dns server will load balance queries to gtms so I think the global availability method will not work.

thanks,

It sounds like you'll want to have both of your GTMs in a sync group. That way, their configurations will be the same and no matter which GTM the query arrives at, both will provide the same resolution.

The authoritative DNS server that will delegate the domains to your two GTMs will need to be configured to delegate to both. When a client requests an NS record for the domain, your authoritative server will hand back both of your GTM hostnames/IP addresses. The client will then try to query one. If non-responsive, it should try querying the other. If both GTMs are non-responsive, then the query will fail.

You can configure global availability as your load balancing method on the GTMs. Keep in mind what that will do is just control the method which GTM responds to client queries. It won't affect how your parent authority delegates domains to your GTMs. If round robin will work, then global availability will too. Just a different balancing algorithm.