240 ServerIron ADX Global Server Load Balancing Guide
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Displaying GSLB for IPv6 configurations
2
The command can be used with or without the <zone-name> variable, which specifies a single
zone. If this variable is omitted, all zones are displayed.
ServerIronADX(config)# show gslb dns zone brocade.com
ZONE: brocade.com
HOST: www:
(Global GSLB policy)
GSLB affinity group: global
Flashback DNS resp.
delay selection
(x100us) counters
TCP APP Count(%)
* 2001:db8::abc: cfg v-ip ACTIVE N-AM. 0 0 1 (33%)
* 2001:db8::def: cfg v-ip ACTIVE N-AM. 0 0 1 (33%)
* 2001:db8::1: cfg v-ip ACTIVE N-AM. 0 0 1 (33%)
* 2001:db8::5: cfg real-ip DOWN N-AM. -- -- 0 (0%)
In the example above, the GSLB controller learned about all the IP addresses associated with the
zone brocade.com from the IP list; thus, the source for each is listed as “cfg”. Traffic has been
evenly distributed across the three active IP addresses.
Clearing DNS selection counters
The GSLB ServerIron ADX maintains DNS selection statistics for each IP address based on DNS
requests served for a particular domain name. These DNS selection statistics include:
•How many times the IP address was selected as the best IP address
•Which metrics were used for making the IP address selection
•The percentage of times an IP address was selected in comparison with other IP addresses in
the same domain name
Use the show gslb dns zone command to display the DNS selection statistics.
DNS selection statistics are used to implement GSLB metrics such as least response, weighted site
and weighted IP metrics. Each of these metrics base subsequent selections on the number of
times the IP address was previously selected. For example, the weighted site metric selects the IP
address that has the least relative weight, the calculation of which is based on the selection
counter of that IP address.
It can be advantageous to use the clear DNS selection counters feature in conjunction with GSLB
metrics. Consider the following examples:
•The least response selection metric selects the IP address that has been selected the least
number of times when compared to other IP addresses. If an IP address has become available
after having been down for some time, it might suddenly become flooded with subsequent
traffic because its selection counter is low. Clearing the counters for that zone can prevent a
flood to this IP address.
•You can also use this feature to test the GSLB implementation before deploying it on a wider
scale. You can analyze the effectiveness of each GSLB metric by rearranging the metric order
and using the Clear Counters feature to start over without having to reload the software.
To clear DNS selection counters globally or per zone, without reloading the software, or to clear out
any DNS requests for any client, enter a command such as the following:
ServerIronADX# clear gslb dns zone zone1