In an Active/Active GSLB setup, what is the order for calculating RTT when using the IdnsprobeOrder DNS PING TCP setting?

• A. The order to calculate the Empty Domain Service (EDS) for Dynamic proximity will be the DNS UDP query followed by the PING and then TCP.
• B. The order to calculate the Round-trip time (RTT) for Dynamic proximity will be the DNS UDP query followed by the PING and then TCP.
• C. The order to calculate the Time to live (TTL) proximity will be the DNS UDP query followed by the PING and then TCP.
• D. The order to calculate the Multiple IP responses (MIR) for Dynamic proximity will be the DNS UDP query followed by the PING and then TCP.

Answer: (B)

In this setup, dynamic proximity uses a specific sequence of probes to build the RTT metric. When the IdnsprobeOrder is set to DNS PING TCP, the system first measures the DNS UDP query RTT, then the PING RTT, and finally the TCP RTT. The overall proximity decision uses the result of this ordered sequence, capturing DNS resolution time, network path latency, and the application-layer connection overhead.

Measuring DNS first makes sense because it includes resolution delays and any caching or resolver-related latency. Adding the ICMP PING step then samples network reachability and latency to the target, and completing with the TCP RTT accounts for the time to establish a connection, which many end-to-end paths hinge on. Together, this order provides a fuller picture of end-to-end latency for proximity decisions.

Other proximity concepts (EDS, TTL-based proximity, MIR) describe different ways to gauge or influence placement and are not describing the RTT measurement sequence dictated by this setting.