Brocade Communications Systems 12.4.00 manual Round-trip times, Passive RTT gathering

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		CPU load	Preference	Location	Connection
Current num.	Session
sessions	util(%)	(%)	(0-255)	EUROPE	Load-Avg
24	0	2	128		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-statefulcommand is not in the configuration. If the ServerIron ADX is configured with the server no-fast-statefulcommand, 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

ServerIron ADX Global Server Load Balancing Guide	141
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