ServerIron ADX Global Server Load Balancing Guide 135
53-1002437-01
Smoothing mechanism for RTT measurements 1
Each successively high RTT sample will be gradually factored into the existing RTT value using
an additive increase. The ramp up factor specifies the step for the additive increase. For
example, if the ramp u p factor is 2 and the n ormal ra mp factor i s 10, then t he percent usage of
the new RTT sample will increase in increments of 2 until it reaches 10, as follows: 1,3,5,7,
9,10. Note that the upper boundary (10 in this example) is determined by the normal ramp
factor.
If you set a high value for maximum ignore count, then you may want the RTT value to ramp up
quickly because the GSLB ServerIron ADX has already ignored enough RTT samples with high
values. If GSLB ServerIron ADX is still seeing high values, this means they are not anomalies. In
reality the RTT has increased and GSLB ServerIron ADX needs to factor this increased RTT into
the existing RTT value quickly. You can set the ramp up factor to a higher value in order to
achieve this.
NOTE
You may need to fine-tune both ramp up factor and the normal ramp factor if a faster ramp up
in the RTT value is desired
•Ramp down factor: This parameter specifies the factor by which successively new very low RTT
samples should be factored into the existing RTT value.
Each successively low RTT sample will be factored into the existing RTT value using a
multiplicative decrease. The ramp up factor specifies the step for the multiplicative decrease.
For example, if ramp down factor is 3 and normal ramp factor is 10, then the percent usage of
the new RTT sample will be in multiples of 3 until it reaches 10, as follows: 1,3,9,10. Note that
the upper boundary is determined by the normal ramp factor.
Again as described earlier, if you had set a high value for maximum ignore count, then you may
want the RTT value to ramp down quickly. You can set the ramp down factor to a higher value in
order to achieve this.
NOTE
You may need to fine-tune both ramp down factor and the normal ramp factor if a faster ramp
down in the RTT value is desired
Enabling enhanced RTT smoothing
Enhanced RTT smoothing is disabled globally by default. You can enable enhanced RTT smoothing
globally or per GSLB site.
Once enhanced RTT smoothing is enabled, you can configure the parameters for the feature. These
parameters are configured for each site at the Site-level. This means that each site can have its
own set of enhanced RTT smoothing parameters.
To enable enhanced RTT smoothing globally for all GSLB Sites, enter commands such as the
following:
GSLB-ServerIronADX# configure terminal
GSLB-ServerIronADX(config)# gslb enhanced-rtt-smoothing
Syntax: gslb enhanced-rtt-smoothing
To enable enhanced RTT smoothing for a GSLB Site, enter commands such as the follow ing:
GSLB-ServerIronADX# configure terminal
GSLB-ServerIronADX(config)# gslb site sanjose
GSLB-ServerIronADX(config-gslb-site-sanjose)# enable-site-rtt-smoothing