Brocade Virtual ADX Global Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 22)

12 Brocade Virtual ADX Global Server Load Balancing Guide
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Global Server Load Balancing overview
1
Round Robin Selection
The Round Robin Selection metric is an alternative to the Least Response Selection metric as the
final tie breaker. When you enable Round Robin Selection, the GSLB Brocade Virtual ADX
automatically disables the Least Response Selection metric, and instead uses the round-robin
algorithm to select a site. Round Robin Selection chooses the first IP address in the DNS response
for the first client request, then selects the next address for the next client request, and so on.
Use the Round Robin Selection metric instead of the Least Response Selection metric when you
want to prevent the GSLB Brocade Virtual ADX from favoring new or recently recovered sites over
previously configured active sites. The Least Response metric can cause the GSLB Brocade Virtual
ADX to select a new site or a previously unavailable site that has come up again instead of
previously configured sites for a given VIP. This occurs because the GSLB Brocade Virtual ADX has
selected the new site fewer times than previously configured sites for the VIP.
In some cases, the Least Response Selection metric can cause the GSLB Brocade Virtual ADX to
send client requests to a new or recovered site faster than the site can handle while it is coming up.
To avoid this situation, you can configure the GSLB Brocade Virtual ADX to use the Round Robin
Selection metric instead of the Least Response Selection metric as the final tie breaker.
The Round Robin Selection metric is disabled by default.
Check the current and maximum values for GSLB resources using the show gslb resource CLI
command.
Virtual ADX#show gslb resources
GSLB resource usage:
Current Maximum
sites 0 128
SIs 0 200
SIs' VIPs 0 2048
dns zones 0 1000
dns hosts 0 1000
health-checks app. 0 1000
dns IP addrs. 0 2048
affinities 0 1024
affinity groups 0 128
static prefixes 0 250
RTT entries 0 10000
GSLB host policies 0 100
IPv4 Statistics Current Maximum
user geo prefixes 0 512
prefix cache 0 11786
IPv6 Statistics Current Maximum
user geo prefixes 0 512
prefix cache 35 11786
Health check Current Maximum
VIPs 0 32
Reals 0 256