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Identifying Equal Cost Multiple-Paths

  1. Right-click on the topology map and select Labels > Link Labels > Show Link Metrics.
    Figure 1: Show Link Distance
    Show Link Distance
  2. The link distances will be displayed and we can see that in this network, every metric has been set to 10. This is very likely to cause numerous equal cost multiple-paths to exist.
    Figure 2: Topology Map with Link Distances
    Topology Map with Link Distances
  3. Select Report > Report Manager to open up the Report Manager.
  4. Select Network Reports > Demand Reports > Equal Cost Multi-Path Report from the left panel to bring up the report listing all of the equal cost multiple-paths of the network. As can be seen in Figure 3, there are many such paths. This report is also saved on the server as EQPATHRPT. runcode. Note that the ECMP paths are calculated based on IP metric only, and do not factor in the influence of MPLS traffic engineering tunnels on the demand routing.
    Figure 3: Equal Cost Multiple-Paths Report
    Equal Cost Multiple-Paths
  5. Select Network > Path & Capacity > Equivalent Path to bring up the Demand Equivalent Path window.
    Figure 4: Network > Path & Capacity > Equivalent Path
    Network > Path & Capacity > Equivalent Path
  6. Select Node A and Node B, then click Show Path. The Path window will be displayed.
    Figure 5: Demand Equivalent Path
    Demand Equivalent Path
  7. All of the equivalent paths between the two selected nodes will be displayed in the Paths window. Select a path to view its detailed information and highlight it on the topology map.
    Figure 6: Equivalent Cost Paths
    Equivalent Cost Paths

    Reducing Equal Cost Multiple Paths

  8. If you choose your link metrics wisely (such as using the real distance in miles like in Figure 7), you can increase the variability of the path costs which will make it less likely for equal cost multiple-paths to occur.
    Figure 8: Routing according to Actual Mileage
    Routing according to Actual Mileage
  9. Open up the Equal Cost Multi-Path Report again and you will see that there are no longer any equal cost multiple-paths in the network with the new link metrics.
    Figure 9: New Equal Cost Multiple-Paths Report
    New Equal Cost Multiple-Paths Report