CCNA Exam Preparation / OSPF and resiliency
CCNA technique 138: OSPF fault isolation — practice and verify
An original CCNA exercise on ospf fault isolation with predictions, evidence, and a changed-condition check.
Environment and inputs: CCNA 200-301 v1.1 study; isolated Cisco IOS / IOS XE lab or paper exercise where applicable.
Practice task
Check neighbor state, installed routes, and next-hop reachability in that order for a failed remote subnet ping.
Expected reasoning
An absent neighbor, a missing prefix, and failed data forwarding are different diagnostic stages.
Produce evidence
Use an isolated simulator, approved lab or paper trace. Record the topology, prediction and observed result. Before device changes, capture the relevant interface, route, neighbor or service state. Ping alone may not prove the behavior under study.
Introduce a counterexample
Change one condition in the ospf fault isolation exercise and predict the result before checking it. Explain which observation would disprove your hypothesis. Restore the baseline, repeat from blank notes and keep both results.
Exam scope
Independent CCNA 200-301 v1.1 exercise, checked against Cisco resources on 2 November 2026. It is not a recalled exam question. The collection’s 200 techniques do not represent exam question counts or weights. Check Cisco’s current exam rules and your simulator’s supported syntax.