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GSS-Concept Misunderstanding

GSS is used to load balancing/redundancy method that can be used if you have two different sites and two public ip blocks.  However, I'm not quite understanding how GSS accomplishes this based on a couple of issues.

Even with GSS, arent we still relying on the global DNS to provide redundancy?  In other words, if we register a GSS as our authoritative name servers instead of a true DNS servers so they can do the load balancing/failover based on their configurations/algorithms, its still the global DNS servers that determine which GSS to go to for primary or secondary GSS.  Hence, take an example where I have two datacenters and two different ISPs.   I point everything to my primary GSS at ISP1 to handle the load balancing of dns requests, whether it does it itself or redirects it to another GSS at datacenter2 on ISP2.  That primary datacenter loses connection and hence that primary GSS becomes unresponsive.  The secondary global DNS record would then point to the secondary GSS at a secondary IP address.  The secondary GSS has been synced with the primary and everything is good to go.  However, if you notice we are relying on the global dns to failover to the secondary GSS.  The problem I see here and correct me if my understanding is wrong, the global dns will send the request to the primary, it wont receive a reply, then send the request to the secondary name server (GSS).  It will do this for every request. It wont know to stop querying the primary and start going to the secondary.  This creates a constant delay as it always try the primary first.  Another issue with this is many DNS servers have already cached our primary name server (primary GSS). and hence the cache has to be updated before they will send the request to the secondary name server( secondary GSS).  Again, this could create huge delays similar to te 24-48 hour delay when changing name server ip addresses.