First-Hop Redundancy Troubleshooting

Bundle lab · $29.99

Troubleshoot and repair a pre-broken HSRP gateway on a single shared LAN. Two routers (R1, R2) and two clients (PC1, PC2) connect to a single L2 switch (SW1) in VLAN 10. The hosts intermittently lose gateway reachability because both routers act active due to seeded faults. Use show commands to diagnose, then correct HSRP so both routers share one virtual IP and R1 deterministically wins active.

Learning objectives

• Diagnose HSRP faults using show standby and show standby brief output.
• Identify and correct a mismatched HSRP virtual IP so both routers form a single redundancy pair.
• Establish deterministic active/standby roles by configuring priority and preempt correctly.
• Validate host default gateway stability from Linux clients without reconfiguring host IP settings.

Troubleshooting focus

• If hosts intermittently lose the default gateway, first verify they all point to the same virtual IP and not a physical router IP.
• On both routers, compare HSRP group number, virtual IP, and state in show standby brief; mismatches cause each router to become active independently.
• If the wrong router is active, compare configured priority and whether preempt is enabled on the intended primary.
• Confirm only one virtual MAC/IP is advertised by checking ARP on the hosts for flapping or duplicate entries.