Brocade Communications Systems ServerIron ADX 12.4.00 - Manual (Page 18)

6 ServerIron ADX Global Server Load Balancing Guide
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Global Server Load Balancing overview
1
servers that receive the records retain them in their databases for only 10 seconds. After the ten
seconds expire, subsequent requests from the client initiate another query to the authoritative DNS
server. As a result, the client always receives fresh information and the address of the site that is
truly the best site for the client.
NOTE
You also can change the TTL if needed. However, Brocade recommends that you do not change the
TTL to 0, because this can be interpreted as an error by some older DNS servers.
You identify each ServerIron ADX by its management IP address, not by any VIPs configured on the
ServerIron ADX. Optionally, you also can specify a name for each ServerIron ADX at the site.
If a remote site is managed by one or more ServerIron ADXs, the GSLB ServerIron ADX gathers
additional information from the site ServerIron ADXs using GSLB protocol with the remote
ServerIron ADXs. The protocol uses TCP port 182. To initiate the GSLB protocol between the GSLB
ServerIron ADX and the ServerIron ADXs at the remote sites, you must first enable the GSLB
protocol on those remote ServerIron ADXs, then identify the sites and the ServerIron ADXs. In this
example, the GSLB ServerIron ADX is configured with site information for Site 1 in Sunnyvale and
Site 2 in Atlanta. Each site has servers containing the content for domain names within the domain
brocade.com. The servers are load balanced by the ServerIron ADXs.
GSLB policy
The ServerIron ADX can use the following metrics to evaluate the server IP addresses in a DNS
reply:
• The server’s health
• The weighted IP value assigned to an IP address
• The weighted site value assigned to a site
• The site ServerIron ADX’s remote SI session capacity threshold
• The IP address with the highest number of active bindings
• The round-trip time between the remote ServerIron ADX and the DNS client’s subnet
• The geographic location of the server
• The connection load
• The site ServerIron ADX’s available session capacity
• The site ServerIron ADX’s FlashBack speed (how quickly the GSLB receives the health check
results)
• The site ServerIron ADX’s administrative preference (a numeric preference value you assign to
influence the GSLB policy if other policy metrics are equal)
• The Least Response selection (the site ServerIron ADX that has been selected less often than
others)
• Round robin selection (an alternative to the Least Response metric)
NOTE
The default order for the metrics is the order shown above.
The GSLB ServerIron ADX evaluates each IP address in the DNS reply based on these metrics.
Based on the results, the GSLB ServerIron ADX can reorder the list to place the IP address for the
“best” site on the top of the list.