Brocade Communications Systems ServerIron ADX 12.4.00 - Manual (Page 153)

ServerIron ADX Global Server Load Balancing Guide 141
53-1002437-01
Round-trip times
1
GSLB-ServerIronADX(config-gslb-rtt-sim-test)# exit
Note that the resulting RTT value obtained after smoothing the following set of RTT samples
(30,1,1000,30,30,30,30) using the old smoothing mechanism is 90.0. The result and is 28.96
with the enhanced smoothing mechanism.
Determining if the new RTT smoothing mechanism is enabled
To determine if the new RTT smoothing mechanism is enabled or disabled for a GSLB Site, enter
the following command.
GSLB-ServerIronADX# show gslb site local
SITE: local
Enhanced RTT smoothing: ON
ServerIron: 1.1.1.102:
state: SELF
Protocol Version: 2
distributed health-chk
Current num. Session CPU load Preference Location Connection
sessions util(%) (%) (0-255) Load-Avg
24 0 2 128 EUROPE 0
Virtual IPs:
1.1.1.101(A) 1.1.1.76(A)
Syntax: show gslb site <site-name>
The output above shows that the new RTT smoothing mechanism is enabled for GSLB Site "local".
Round-trip times
Brocade GSLB supports both passive and active round-trip time (RTT) gathering to determine the
round-trip times between a Site ServerIron ADX and a client.
Passive RTT gathering
Passive RTT gathering uses the existing flow of traffic between the client and the Site ServerIron
ADX to gather RTT. Whenever a client opens a TCP connection with the Site ServerIron ADX, the Site
ServerIron ADX computes the round-trip time (RTT) as the amount of time that passes between the
time the Site ServerIron ADX receives the TCP connection (TCP SYN) from the client, and when it
receives the client’s acknowledgment of the connection request (TCP ACK).
The Site ServerIron ADX uses the GSLB protocol to report the RTT to the GSLB ServerIron ADX. The
GSLB ServerIron ADX uses this RTT information as a metric when comparing IP addresses in the
DNS reply to select the optimal IP address for the client.
NOTE
Passive RTT information is not gathered on the remote site ServerIron ADX if the ServerIron ADX only
processes basic load balance traffic and the server no-fast-stateful command is not in the
configuration. If the ServerIron ADX is configured with the server no-fast-stateful command, the
passive RTT information will be gathered on the remote site ServerIron ADX and sent out to the GSLB
controller. If other Sever Load Balancing features such as L7 switching (CSW switching) are