How do you troubleshoot issues with HSRP or VRRP?

Troubleshooting High Availability (HA) protocols such as Hot Standby Router Protocol (HSRP) or Virtual Router Redundancy Protocol (VRRP) involves a systematic approach to identify and resolve issues. These protocols are used to provide network redundancy by allowing multiple routers to work together in a group, with one router acting as the active router and the others as standby routers.

  1. Verify Configuration:
    • Ensure that HSRP or VRRP is configured correctly on all routers in the group.
    • Verify that the virtual IP address and virtual MAC address are configured identically on all routers in the group.
    • Confirm that the priority values are set correctly, with the highest priority designating the active router.
  2. Check Interface Status:
    • Verify the physical and logical status of the interfaces participating in the HSRP or VRRP group.
    • Confirm that there is connectivity between routers over the configured interface.
  3. Check State and Priority:
    • Use the show standby (for HSRP) or show vrrp (for VRRP) commands to check the state and priority of each router in the group.
    • Ensure that the router with the highest priority becomes the active router.
  4. Check Communication Between Routers:
    • Verify that there is no network partition or communication issue between routers.
    • Use tools like ping or traceroute to test connectivity between routers.
  5. Review Logs and Notifications:
    • Check the router logs for any error messages or notifications related to HSRP or VRRP.
    • Use commands such as show logging or show log to view system logs.
  6. Verify Virtual IP Reachability:
    • Confirm that devices on the network can reach the virtual IP address.
    • If there are issues, it might indicate a problem with ARP resolution or incorrect IP settings.
  7. Check for Duplicate IP Addresses:
    • Verify that there are no duplicate IP addresses in the network that may conflict with the virtual IP address.
  8. Verify HSRP/VRRP Version Compatibility:
    • Ensure that all routers in the HSRP or VRRP group are running the same version of the protocol.
  9. Check for HSRP/VRRP Preemption:
    • Confirm whether preemption is configured and working correctly. Preemption allows a higher-priority router to reclaim the active role when it becomes available.
  10. Check Physical Layer:
    • Inspect the physical layer for issues, such as faulty cables or hardware problems.
  11. Use Debug Commands Sparingly:
    • If necessary, use debug commands such as debug standby or debug vrrp with caution to gather real-time information. Be mindful of the potential impact on the router's performance.
  12. Consult Documentation and Online Resources:
    • Refer to the router's documentation and online resources for specific troubleshooting steps and potential solutions.