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To configure a
Syntax:
Probes for RTT gathering
By default, a Site ServerIron ADX on which active RTT gathering is enabled uses an ICMP prober to gather active RTT values. In addition to ICMP prober, a DNS prober can also be enabled on the Site ServerIron ADX. The DNS prober gathers RTT actively by sending a DNS query to the LDNS server and calculating RTT for that LDNS server when it receives the corresponding DNS response.
The DNS prober is disabled by default. If you enable the DNS prober, then the Site ServerIron ADX gathers RTT using both ICMP prober and DNS prober and reports measurements from their probes to the GSLB controller.
Accepting DNS RTT measurements
If DNS prober is enabled on the Site ServerIron ADX, then the GSLB ServerIron ADX receives the DNS RTT measurements in addition to the ICMP RTT measurements from that Site ServerIron ADX. By default, the GSLB ServerIron ADX does not use the DNS RTT measurements reported by Site ServerIron ADXs.
You need to enable the GSLB ServerIron ADX to accept DNS RTT measurements reported by Site ServerIron ADXs. Also, you need to indicate if a fallback mechanism should be used between the DNS RTT measurements and the ICMP RTT measurements. If the fallback mechanism is disabled, ICMP RTT value is used as the primary RTT value. If the fallback mechanism is enabled, DNS RTT value is used as the primary RTT value and ICMP RTT is used as the secondary RTT value.
During selection of the best IP address for a client, the GSLB ServerIron ADX will always use the primary RTT value. If the primary RTT value has failed or is unavailable, then the GSLB ServerIron ADX will use the backup RTT value only if the fallback mechanism on the GSLB ServerIron ADX has been enabled.
To enable the GSLB ServerIron ADX to accept DNS RTT measurements and to enable fallback mechanism, enter the following on the GSLB ServerIron ADX.
Syntax: gslb dns-probe enable-fallback
To enable the GSLB ServerIron ADX to accept DNS RTT measurements but to disable fallback mechanism, enter commands such as the following on the GSLB ServerIron ADX.
Syntax: gslb dns-probe disable-fallback
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