Systematic Troubleshooting and Debugging Questions

Covers structured methods for diagnosing and resolving software defects and technical problems at the code and system level. Candidates should demonstrate methodical debugging practices such as reading and reasoning about code, tracing execution paths, reproducing issues, collecting and interpreting logs metrics and error messages, forming and testing hypotheses, and iterating toward root cause. Topic includes use of diagnostic tools and commands, isolation strategies, instrumentation and logging best practices, regression testing and validation, trade offs between quick fixes and long term robust solutions, rollback and safe testing approaches, and clear documentation of investigative steps and outcomes.

EasyTechnical

33 practiced

After a trunk change, hosts in VLAN 20 cannot reach the 10.20.0.0/24 network while VLAN 30 is unaffected. Describe step-by-step how to test whether this is a VLAN-tagging/trunking issue, including exact show/diagnostic commands, checks for native VLAN mismatches, and how to verify trunk encapsulation on both ends.

MediumTechnical

32 practiced

A recent firewall policy change may have caused intermittent business-critical application failures. Design an isolation test plan to verify whether the policy is responsible without removing the policy globally. Include how to use policy hit counters, targeted test traffic, logs, and safe rollback criteria.

HardTechnical

29 practiced

Draft an outline for a high-quality postmortem template for complex network incidents that ensures clear root cause, timeline, contributing factors, corrective actions, validation tests, and owners. List artifacts to attach (pcaps, configs, alerts), how to calculate SLO impact, and how to use the postmortem to prevent recurrence.

HardTechnical

48 practiced

Several prefixes are blackholed after a recent route-filter change was applied across routers. Provide a step-by-step root-cause analysis plan to find the device that introduced the misconfiguration, outline how to rollback safely, and describe verification steps to ensure prefixes are fully restored. Mention route collectors, config version control, and RPKI checks.

EasyTechnical

39 practiced

Multiple laptops on VLAN 40 are failing to obtain DHCP leases while other VLANs are fine. Describe the litmus tests and commands you would run on the client and DHCP server, what logs to inspect, how to verify DHCP relay/forwarding, and how to determine whether the problem is scope exhaustion, relay misconfiguration, or switch port isolation.

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