AdvancedPublished 2026-07-02
First-Hop Redundancy Troubleshooting
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Lab 13 of 13 in First-Hop Redundancy (HSRP & VRRP) · ← Previous
CCNA exam domain: IP Connectivity
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.
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How this lab is graded
- Build it your way. Where a lab lets you choose a value — a VLAN name, an interface description — grading checks that you configured it, not which name you picked. Names that another line has to reference, like an ACL applied with
access-class, are stated in the guide and do have to match. - Addresses, modes and protocol keywords are exact. An IP address, a subnet mask,
switchport mode trunk, an encapsulation — these carry the meaning of the lab, so they are graded as written in the guide. - Grading reads your saved configuration. Export the lab from CML after you have configured it, and make sure anything you set is in the
running-config— a change that only exists in a terminal session never reaches the grader. - You can submit as many times as you like. Your best score stands, and each attempt tells you which checks passed so you can work the gaps.
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