IntermediatePublished 2026-09-21
CCNA Break/Fix: Everything Is Crossing the Backup Circuit
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Lab 7 of 13 in CCNA Break/Fix II: Read the Symptom · ← Previous · Next →
CCNA exam domain: IP Connectivity
Two sites have dual WAN links (primary and backup). Both circuits are up and end-to-end connectivity works, yet every intersite flow rides the slow backup path. Your job: read which routes each router actually installed for the opposite site and why, then restore the intended path preference so traffic uses the primary circuit while keeping the backup standing by.
Learning objectives
- Diagnose why intersite traffic prefers the backup link even though both circuits are up
- Trace route selection on each router and compare installed vs candidate static routes
- Distinguish the administrative preference causing a less-preferred path to win
- Verify the corrected path selection from end hosts using ping and traceroute
Troubleshooting focus
- Start from the symptom: traceroute from the branch PC to the HQ server shows a 10.0.13.x hop (backup) instead of 10.0.12.x (primary).
- On each router, trace the exact route chosen for the opposite site’s LAN and loopback; compare the installed route’s preference against the intended design.
- Confirm both WAN interfaces are up/up and addressed correctly; do not proceed until Layer 1/2 is healthy.
- Check that a higher-preference candidate exists for the primary path and that the backup route remains present as a floating option.
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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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