Important Notes and Limitations for BWOpt
Consider the following notes and limitations when using BWOpt:
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Only traffic that is not in an SR policy or existing BWOpt SR policy can be rerouted to mitigate congested links. BWOpt will not shift traffic in existing SR policies that it did not create. This may prevent it from being able to mitigate congestion if most of the traffic on the congested link is in non-BWOpt SR policies.
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BWOpt relies on the PCC's autoroute feature to steer traffic into the tactical SR policies it creates. Autoroute is applied to these policies through the proper Profile ID option set in BWOpt (to align with configuration on the PCC associating that Profile ID with autoroute feature). This is critical to tactical SR policies shifting traffic away from congested links.
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BWOpt does not support multi-area or multi-level IGP (see "IGP and Inter-AS Support" in the Cisco Crosswork Optimization Engine Installation Guide). Autoroute will not properly steer traffic onto inter-area or inter-level tactical SR policies. So, although they can be provisioned, traffic will not use them. Therefore, BWOpt will be ineffective if enabled in this environment.
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BWOpt uses simulated traffic based on measured SRTM data to determine link utilizations and when to mitigate congestion. The simulated interface utilization that BWOpt monitors should closely align with the SNMP-based interface utilization that is displayed in the Optimization Engine UI. However, due to various factors, including SNMP polling cadence and rate averaging techniques, they may differ at times. This can result in scenarios like a link appearing to be congested in the UI and BWOpt not reacting.
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BWOpt only creates tactical SR policies on PCCs that are sources of SRTM telemetry data. Only these nodes (typically provider edge routers) provide the telemetry-based data needed to create simulated traffic demands in the internal model representing the traffic from that node to other PE nodes in the network.
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Only solutions that produce interface utilization below the threshold (set across all interfaces) will be deployed. If BWOpt is unable to mitigate congestion across the entire network, it will not deploy any tactical SR policies and a “Network Congested. BWOpt unable to mitigate.” alarm is set. This alarm is unset when congestion either subsides on its own or can be addressed successfully through BWOpt tactical SR policy deployments.
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BWOpt temporarily pauses operation whenever the system is unavailable due to a restart or a rebuild of the topology from Topology Services. When this occurs, an alarm indicating this condition is set by BWOpt. During this time, BWOpt will not evaluate congestion in the network. All currently deployed tactical SR policies are maintained, but will not be modified or deleted. As soon as the model becomes available, the alarm is cleared and BWOpt will resume normal operation.