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GSLB-ServerIronADX# configure terminal
GSLB-ServerIronADX(config)# gslb policy
GSLB-ServerIronADX(config-gslb-policy)# round-trip-time active-rtt
use-active-and-passive-rtts
To configure a host-level GSLB policy to use both passive and active RTT values for RTT algorithm
(Mode 3), enter commands such as the following
GSLB-ServerIronADX# configure terminal
GSLB-ServerIronADX(config)# gslb-host-policy test
GSLB-ServerIronADX(config-gslb-host-policy-test)# round-trip-time active-rtt
use-active-and-passive-rtts
Syntax: round-trip-time active-rtt use-active-and-passive-rtts
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.
GSLB-ServerIronADX# configure terminal
GSLB-ServerIronADX(config)# gslb dns-probe enable-fallback
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.
GSLB-ServerIronADX# configure terminal
GSLB-ServerIronADX(config)# gslb dns-probe disable-fallback
Syntax: gslb dns-probe disable-fallback
ServerIron ADX Global Server Load Balancing Guide
53-1002437-01
1
Round-trip times
149
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