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AR Router Troubleshooting Guide

This Product Documentation provides guidance for maintaining AR Enterprise Router, covering common information collection and fault diagnostic commands, typical fault troubleshooting guide, and troubleshooting.
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Interface Backup Fails to Take Effect

Interface Backup Fails to Take Effect

Common Causes

As shown in Figure 23-1, RouterA and RouterB are connected.

Multiple interfaces on RouterA back up one another:
  • Interface1 is the primary interface.
  • Interface2 and interface3 are backup interfaces.
Figure 23-1 Networking diagram of interface backup
Interface backup cannot take effect in the following situations:
  • Backup interfaces become unavailable after the primary interface fails.
  • In load balancing mode, load balancing cannot be implemented among the primary and backup interfaces because they cannot all be in Up state simultaneously.
  • In load balancing mode, traffic cannot be load balanced among multiple interfaces.

This fault is commonly caused by one of the following:

  • The physical status of backup interfaces is Down.
  • The link layer status of backup interfaces is Down.
  • In load balancing mode:
    • The load balancing threshold and maximum bandwidth are not configured for the primary interface.
    • An equal-cost route is not generated.
    • Only one flow needs to be transmitted.

Troubleshooting Flowchart

Figure 23-2 shows the troubleshooting flowchart.

Figure 23-2 Interface backup failing to take effect

Troubleshooting Procedure

NOTE:

Saving the results of each troubleshooting step is recommended. If troubleshooting fails to correct the fault, you will have a record of your actions to provide Huawei technical support personnel.

Procedure

  1. Check that the physical status of the backup interfaces is Up.

    Run the display interface interface-type interface-number command on the local and remote devices to check the current state field.

    • If the current state field is DOWN, check whether the cable is correctly connected and whether interface parameters are correctly set.
    • If the current state field is UP, go to step 2.
  2. Check that the link layer status of backup interfaces is Up.

    Run the display interface interface-type interface-number command on the local and remote devices to check the Line protocol current state field.

    • If the Line protocol current state field is DOWN, check whether IP addresses and link layer parameters are correctly set on the interfaces.
      NOTE:

      When dialer interfaces are used as backup interfaces, IP addresses must be configured to trigger dialup and a routing protocol must be configured on the dialer interfaces.

      When the primary interface fails, dialer interfaces are enabled as backup interfaces. The configured routing protocol sends protocol packets through the dialer interfaces, which triggers dialup and the generation of routes.

    • If the Line protocol current state field is UP, go to step 3.
  3. Check whether the active/standby mode is used for interface backup.

    Run the display this command in the primary interface view to check whether the load balancing threshold and maximum bandwidth are configured for the primary interface.

    • If the load balancing threshold and maximum bandwidth are not configured for the primary interface, the active/standby mode is used for interface backup. Check whether the active/standby mode needs to be used for interface backup according to networking requirements:
      • If the active/standby mode is required for interface backup, go to step 6.
      • If the load balancing mode is required for interface backup, run the standby threshold enable-threshold disable-threshold command on the primary interface to configure the load balancing threshold, and run the standby bandwidth size command to configure the maximum bandwidth for the primary interface.
    • If the load balancing threshold and maximum bandwidth are configured for the primary interface, the load balancing mode is used for interface backup. Go to step 4.
  4. Check whether equal-cost routes are generated.

    If traffic needs to be sent from multiple interfaces to the same destination address, equal-cost routes must be generated to implement load balancing among these interfaces. Run the display ip routing-table command to check whether equal-cost routes are generated. The following command output shows that equal-cost routes are generated.

    <Huawei>display ip routing-table
    Route Flags: R - relay, D - download to fib
    ----------------------------------------------------------------------------
    Routing Tables: Public
             Destinations : 7        Routes : 7
    
    Destination/Mask    Proto   Pre  Cost      Flags   NextHop         Interface
    
            2.2.2.0/24  Static  60    0           RD   192.168.1.2     GigabitEthernet1/0/0
                        Static  60    0           RD   192.168.2.2     GigabitEthernet2/0/0
    

    • If an equal-cost route is not generated, modify the related routing configuration:

      • Modify route attributes, such as the cost.
      • Configure static routes as shown in the preceding command output.
      NOTE:

      The preceding example describes how to load balance traffic destined for the same destination address. If multiple flows are destined for different destination addresses and these flows need to be sent from the primary and backup interfaces, the flows can be load balanced among these interfaces even if no equal-cost route is available.

      The following conditions must be met to implement load balancing:
      • When multiple interfaces among the primary and backup interfaces are working, these interfaces have the routes destined for these destination addresses.
      • To maintain stable load balancing, ensure that the traffic volume of the primary interface is greater than the lower threshold. Otherwise, backup interfaces will be disabled.
    • If equal-cost routes are generated, go to step 5.

  5. Check whether multiple flows are transmitted over the links.

    After equal-cost routes are generated, the device selects a route to forward packets according to the hash algorithm. If only one flow needs to be transmitted, it cannot be load balanced among multiple links. The device load balances traffic among multiple links only when multiple flows need to be transmitted. Check whether multiple flows are transmitted over the links.

    • If only one flow is sent from the primary interface, use the active/standby mode for interface backup.
    • If multiple flows are transmitted over links, but the fault persists, go to step 6.
  6. Collect the following information and contact technical support personnel.

    • Results of the preceding troubleshooting procedure
    • Configuration files, log files, and alarm files of the device

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Updated: 2019-08-09

Document ID: EDOC1000079719

Views: 497538

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