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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 DistanceDialog box titled Link Labels for network configuration with options to show labels and select label text type.
  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 DistancesNetwork topology diagram with interconnected nodes and links labeled 10. Different link colors indicate distinct paths or attributes.
  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 ReportNetwork report interface analyzing Layer 3 ECMP routing with a menu of report categories and a table of ECMP demand paths and details.
  5. Select Network > Path & Capacity > Equivalent Path to bring up the Demand Equivalent Path window.
    Figure 4: Network > Path & Capacity > Equivalent PathDropdown menu in network management software with options for Link Rules, Path and Capacity, Equal Metrics at PE, Show Site Demands, Aggreg Demands, Aggreg Tunnels, Pricer, and Templates.
  6. Select Node A and Node B, then click Show Path. The Path window will be displayed.
    Figure 5: Demand Equivalent PathGraphical user interface for Demand Equivalent Path tool showing dropdowns for Node A and Node Z, fields for IP and IPv6 addresses, owner, bandwidth, path type, priority settings, and buttons for highlighting nodes, showing paths, and help.
  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 PathsNetwork visualization tool interface with two panels: top panel lists network paths, interface details, IPs, tunnel types, and destination nodes; bottom panel shows a network map with color-coded links indicating utilization levels from green to red.

    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 DistancesNetwork diagram with nodes connected by colored lines indicating distances or weights. Different icons represent network devices or locations.
    Figure 8: Routing according to Actual MileageSoftware interface for configuring IP/MPLS network options with settings for Max Hop, Routing Method, and Path Selection.
  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 ReportReport Manager software interface for managing Layer 3 network reports, showing no equal cost multi-paths between node pairs.