What happens when the data center that GTM recommends for a client is unavailable?

GTM does not fall back to cached routing information - it uses real-time health monitoring data and its live pool configuration to actively select the next available resource.

GTM does not query the local DNS server to find an alternate route - the failover decision is made internally by GTM based on its own pool member health states and load balancing logic.

GTM uses health monitors to continuously track the availability of data centers and their resources. When the top-ranked data center is determined to be unavailable, GTM immediately directs the next incoming DNS query to the next preferred data center as ranked by the configured load balancing method (such as round robin, global availability, or ratio). This failover occurs at the DNS resolution layer, ensuring clients always receive an IP address pointing to a healthy, reachable resource.

GTM does not instruct clients to consult their own DNS cache - GTM itself responds with a fresh DNS answer resolving to an available data center's IP address.

The client does not persist in attempting the unavailable data center because GTM resolves the issue at the DNS layer by returning a different IP address for a healthy data center.