While basic PfR cost-based optimization can be useful, many organizations have multiple border router exit links and possibly several different service providers charging different billing rates that increase according to the bandwidth utilized. In this situation, some form of traffic load balancing across the links may be required in addition to the cost minimization policy.
Perform this task on the master controller to configure a Performance Routing cost policy to minimize the monthly billing charge for multiple border router exit links while load balancing traffic across the links. In this scenario, the network has both fixed-rate and tier-based billing, and assuming that the customer is paying a monthly fee for the fixed-rate billing and the pre-paid (lowest cost) tier of tier-based billing, PfR can perform traffic load balancing while optimizing for cost.
The figure below shows an example of how different billing rates can be defined for each link using bandwidth and cost parameters that are defined through service level agreements (SLAs) that are identified as rules in the diagram. The main goal of this task is to minimize the billing charge per exit link and to load balance traffic across the exit links. Although Link 1 may be billed at a fixed-rate and Links 2 through 4 are subject to tier-based billing, all the links are set up as PfR tiers. To accomplish the cost minimization the first rule is to utilize 80 percent of Link 1 and 30 percent of Links 2, 3 and 4, as shown in the figure below. The second rule is to distribute additional traffic across Links 2, 3 and 4 to balance the traffic load. To achieve the traffic load balancing while minimizing cost, the solution is to configure a PfR cost policy using multiple tiers representing bandwidth percentages that are assigned artificial costs to ensure that the PfR traffic is optimized for cost and load balanced across all the exits. To illustrate the configured tiers, see the figure below.
The steps in this task create a cost policy in which PfR is configured to direct traffic through any of the lowest cost exits first; Link 1 at 10.1.1.1 and the pre-paid tier of the other three exits. When the pre-paid tier bandwidth at each link is fully utilized, the software determines the next lowest incremental cost between the tiers at all the links. The incremental cost of utilizing the next tier at Link 1 is $990. The incremental cost of utilizing the next tier at Link 2 is only $10. PfR forwards traffic to the next lowest cost tier which is the blue bar representing 40 percent of the bandwidth at Link 2, as shown in the figure below. The process continues to use cost to balance the load across Links 2, 3, and 4. This task illustrates how the monthly billing rate per exit link is minimized by utilizing the pre-paid bandwidth at Links 1 though 4 first, and then the traffic is effectively load balanced across Links 2, 3 and 4 by determining the lowest incremental cost between tiers.
|Figure 1 ||Diagram Showing PfR Cost-Minimization Solution to Minimize Billing and Load Balance Traffic |
In the following task steps, the exit link 10.1.1.1 is configured as a tier-based link although it is actually charged at a fixed rate. If a fixed rate link is configured as a tier for load balancing, the monthly cost calculation will not reflect the true cost for that link. Using this solution, the artificial costs assigned to the multiple tiers may affect the accuracy of all the monthly cost calculations.
Only some of the configuration steps for this task scenario are shown in the summary and detailed steps, the full configuration for the master controller is displayed in the Examples section shown after the detailed steps table.
Disable the range and utilization policy priorities because they may conflict with this application of the cost-minimization feature.
Do not configure the periodic or the set periodiccommand with a time interval to avoid system churn as the system tries to select the best exit link at specified intervals. This command is disabled by default.
The cost-minimization command contains many variations of keywords and arguments. Only one of the required keywords and its associated syntax can be configured on one CLI line, but multiple instances of this command can be entered. Only the fixed and tier keywords are mutually exclusive within the configuration for each border router link. For details about the full syntax, see the Cisco IOS Optimized Edge Routing Command Reference.
For another example of configuring cost-minimization and balancing traffic load, see the configuration example Using a PfR Cost Policy to Minimize Billing and Load Balance Traffic Example.