IntermediatePublished 2026-08-26
CCNA Break/Fix: The OSPF Neighbour That Never Forms
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Lab 3 of 7 in CCNA Break/Fix: Diagnose and Repair · ← Previous · Next →
CCNA exam domain: IP Connectivity
A regional retailer's branch lost core access after last night's maintenance window. Users reach their gateway and the routers ping across the transit, but no OSPF neighbour appears and the branch LAN is missing from the core's table. The documented design is OSPF process 1, area 0 on both routers. Restore the adjacency without changing addressing or adding static routes.
Learning objectives
- Diagnose an OSPF adjacency that never forms
- Compare each router's OSPF configuration against the documented design with
show ip protocolsandshow ip ospf interface brief - Confirm
show ip ospf neighborlists a FULL adjacency on both routers - Verify the branch LAN installs as an OSPF route on RTR-CORE-01
- Prove CLIENT10 reaches 10.255.0.2 end to end
Troubleshooting focus
show ip ospf neighboris empty on both routers. Look in the OSPF configuration, not the routing table.- CLIENT10 reaches 10.255.0.1 but not 10.255.0.2. Neither router has an OSPF-learned route in its table.
- CLIENT10 and CLIENT20 reach each other and their gateway. The access switch is not the problem.
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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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