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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 Dialog box titled Link Labels with sections for Show Labels for and What Text with OK and Cancel buttons.
  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 Network topology diagram with interconnected nodes and links labeled 10 indicating possible bandwidth or costs.
  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 Network analysis tool interface showing Layer 3 ECMP routing details with hierarchical menu and toolbar for report management.
  5. Select Network > Path & Capacity > Equivalent Path to bring up the Demand Equivalent Path window.
    Figure 4: Network > Path & Capacity > Equivalent Path Dropdown menu with options for network path and capacity management. Highlighted: Equivalent Path under Path and Capacity.
  6. Select Node A and Node B, then click Show Path. The Path window will be displayed.
    Figure 5: Demand Equivalent Path GUI for network path configuration with node selection, IP address fields, bandwidth, path type, priority settings, and highlight options.
  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 Network visualization tool interface with two side-by-side panels. Each panel shows path information and a network map. Path details include path names, interface info, tunnel types, and node IDs. Network map displays nodes and color-coded links for utilization: red 100 percent, yellow 90 percent, green 75 percent, cyan 50 percent. Panels compare two routing scenarios for network optimization.

    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 7: Topology Map With New Link Distances Network topology diagram with interconnected nodes and links; numbers indicate metrics like bandwidth, and colors suggest connection types.
    Figure 8: Routing according to Actual Mileage Configuration window for IP/MPLS networks, titled Design > Path Placement, with options for max hop, routing method, placement order, path selection, peak rate, MPLS mode, max ECMP count, frame size, PBR check, IGP override, and link balancing. Navigation menu on the left includes General, Design, Device, Failure Simulation, and Report sections.
  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 Report Manager interface displaying EQUAL COST MULTI-PATH INFO mpls-fish with software version, compilation, and report dates. Includes network path symbols and categories like Layer 3 Network Reports and Provisioned Utilization. Options for printing, finding, and navigating are available.