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Load balancing is an integral part of the BIG-IP GTM. Configuring load balancing on a BIG-IP GTM means determining your load balancing scenario, that is, which pool member should receive a connection hosted by a particular virtual server.

A load balancing method is an algorithm or formula that the BIG-IP GTM uses to determine the server to which traffic will be sent. Individual load balancing methods consider one or more dynamic factors, such as current connection count, because each application of the BIG-IP GTM is unique, and server performance depends on several different factors. BIG-IP GTM uses a preferred load balancing method to return the IP address of a virtual server in response to a DNS name resolution request. The preferred method can be either static or dynamic. If the preferred load balancing method fails to return a valid resource in response to a DNS name resolution request, it is likely that BIG-IP GTM was unable to perform load balancing. The alternate method can be only static. If the alternate load balancing method fails to return a valid resource in response to a DNS name resolution request, BIG-IP GTM uses the fallback method. To ensure that BIG-IP GTM returns a response to a request, the fallback method ignores the availability status of a resource. The fallback method can be either static or dynamic. If all of the configured load balancing methods fail to provide a valid resource in response to a DNS name resolution request, either the request fails or BIG-IP GTM uses the local BIND to resolve the request. To understand which load balancing method had been highly used to handle traffic in each pool, the GtmPoolStatTest helps!

This test auto-discovers the pools in the target BIG-IP GTM and for each pool, this test reports the number of times the preferred load balance method/alternate load balance method/fallback load balance method had been used to handle traffic. Using this test, the administrator can understand which load balancing method had been used the most/least to handle traffic in each pool.

Outputs of the test: One set of results for each pool in BIG-IP GTM that is being monitored.

Measurement	Description	Measurement Unit	Interpretation
LoadBal_prefrd	Indicates the number of times which the preferred load balance method is used for this pool during the last measurement period.	Number	Compare the value of this measure across pools to identify the pools that had used this load balancing method.
LoadBal_altrnate	Indicates the number of times which the alternate load balance method is used for this pool during the last measurement period.	Number	Compare the value of this measure across pools to identify the pools that had used the alternate load balancing method.
LoadBal_fallbck	Indicates the number of times which the fallback load balance method is used for this pool during the last measurement period.	Number	Compare the value of this measure across pools to identify the pools that had used the fallback load balancing method.
DnsMsg_dropped	Indicates the number of dropped DNS messages for this pool during the last measurement period.	Number	Ideally, the value of this measure should be 0. If the number of messages lost is abnormally high, it could indicate a bad network connection.