A load balancing virtual server configured to use the least packets method selects the service that has received the fewest packets in the last 14 seconds.

For example, consider three services, Service-HTTP-1, Service-HTTP-2, and Service-HTTP-3.

• Service-HTTP-1 has handled three packets in the last 14 seconds.
• Service-HTTP-2 has handled five packets in the last 14 seconds.
• Service-HTTP-3 has handled two packets in the last 14 seconds.

The following diagram illustrates how the Citrix ADC appliance uses the least packets method to choose a service for each request that it receives.

Figure 1. How the Least Packets Load Balancing Method Works

The Citrix ADC appliance selects a service by using the number of packets (N) transmitted and received by each service in the last 14 seconds. Using this method, it delivers requests as follows:

• Service-HTTP-3 receives the first request, because this service has the lowest N value.
• Since Service-HTTP-1 and Service-HTTP-3 now have the same N value, the virtual server switches to the round robin method. Service-HTTP-1 therefore receives the second request, Service-HTTP-3 receives the third request, Service-HTTP-1 receives the fourth request, Service-HTTP-3 receives the fifth request, and Service-HTTP-1 receives the sixth request.
• Since Service-HTTP-1, Service-HTTP-2, and Service-HTTP-3 all now have the same N value, the virtual server switches to the round robin method for Service-HTTP-2 as well, including it in the round robin list. Therefore, Service-HTTP-2 receives the seventh request, Service-HTTP-3 receives the eighth request, and so on.

The following table summarizes how N is calculated.

Request Received Service Selected Current N Value Remarks
Request-1 Service-HTTP-3; (N = 2) N = 3 Service-HTTP-3 has the lowest N value.
Request-2 Service-HTTP-1; (N = 3) N = 4 Service-HTTP-1 and Service-HTTP-3 have the same N values.
Request-3 Service-HTTP-3; (N = 3) N = 4 Service-HTTP-1 and Service-HTTP-3 have the same N values.
Request-4 Service-HTTP-1; (N = 4) N = 5 -
Request-5 Service-HTTP-3; (N = 4) N = 5 -
Request-6 Service-HTTP-1; (N = 5) N = 6 Service-HTTP-1, Service-HTTP-2, and Service-HTTP-3 have the same N values.
Request-7 Service-HTTP-2; (N = 5) N = 6 Service-HTTP-1, Service-HTTP-2, and Service-HTTP-3 have the same N values.
Request-8 Service-HTTP-3; (N = 5) N = 6 -

Note: If you enable the RTSP NAT option on the virtual server, the appliance uses the number of data and control packets to calculate the number of packets for RTSP services. For more information about the RTSP NAT option, see Managing RTSP Connections.

The Citrix ADC appliance also performs load balancing by using the number of packets and weights when a different weight is assigned to each service. It selects a service by using the value (Nw) in the following expression:

Nw = (N) * (10000 / weight)

As in the preceding example, suppose Service-HTTP-1 is assigned a weight of 2, Service-HTTP-2 is assigned a weight of 3, and Service-HTTP-3 is assigned a weight of 4. The Citrix ADC appliance delivers requests as follows:

• Service-HTTP-3 receives the first second, third, fourth, and fifth requests, because this service has the lowest Nw value.
• Service-HTTP-1 receives the sixth request, because this service has the lowest Nw value.
• Service-HTTP-3 receives the seventh request, because this service has the lowest Nw value.
• Service-HTTP-2 receives the eighth request, because this service has the lowest Nw value.

The following table summarizes how Nw is calculated.

Request Received Service Selected Current Nw Value (Number of Active Transactions) * (10000 / weight) Remarks
Request-1 Service-HTTP-3; (Nw = 5000) Nw = 5000 Service-HTTP-3 has the lowest Nw value.
Request-2 Service-HTTP-3; (Nw = 5000) Nw = 7500 -
Request-3 Service-HTTP-3;(Nw = 7500) Nw = 10000 -
Request-4 Service-HTTP-3; (Nw = 10000) Nw = 12500 -
Request-5 Service-HTTP-3; (Nw = 12500) Nw = 15000 -
Request-6 Service-HTTP-1; (Nw = 15000) Nw = 20000 Service-HTTP-1 and Service-HTTP-3 have the same Nw value.
Request-7 Service-HTTP-3; (Nw = 15000) Nw = 17500 Service-HTTP-1 and Service-HTTP-3 have the same Nw value.
Request-8 Service-HTTP-2; (Nw = 16666.67) Nw = 20000 Service-HTTP-2 has the lowest Nw value.

The following diagram illustrates how the virtual server uses the least packets method when weights are assigned.

Figure 2. How the Least Packets Method Works When Weights Are Assigned

To configure the least packets method, see Configuring a Load Balancing Method that Does Not Include a Policy.

Least packets method