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CCNA Bottom-up troubleshooting Practice Question
Drag and drop the following troubleshooting steps into the correct order to diagnose a client connectivity issue using the OSI bottom-up method. The client cannot access a web server by its FQDN.
⚠ Common exam trap
The trap is that candidates often jump to DNS or IP configuration because the symptom involves an FQDN, but the bottom-up method requires starting at Layer 1. Remember: always start at the bottom of the OSI model when using this approach.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Check physical connectivity (cables, link lights, interface status).
The bottom-up OSI troubleshooting approach starts at Layer 1 (physical) and moves upward. For this scenario (client cannot access web server by FQDN), the correct order is: first check physical connectivity (Layer 1), then check data link layer (Layer 2) for MAC and VLAN issues, then check network layer (Layer 3) for IP configuration, and finally check application layer (Layer 7) for DNS resolution. This systematic approach ensures lower-layer issues are ruled out before investigating higher-layer problems.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Check physical connectivity (cables, link lights, interface status).
Why this is correct
You must always begin with Layer 1. Verify that cables are securely connected, link LEDs are lit, and the interface status shows 'up/up' (or 'connected'). If physical connectivity is absent, no higher-layer configuration can function, so this is the most efficient first step.
- ✓
Verify DNS resolution (nslookup, DNS server reachability).
Why this is correct
DNS resolution is a Layer 7 check that is only meaningful after lower-layer connectivity, IP addressing, and routing are confirmed. If the physical link, VLAN, IP configuration, or default gateway are misconfigured, DNS will fail even if the DNS server is reachable; thus it is the final step in the troubleshooting model.
- ✓
Check IP configuration (IP address, subnet mask, default gateway).
Why this is correct
Checking IP configuration is a Layer 3 task; it must follow Layer 1 and Layer 2 verification because an IP address cannot be assigned or communicated if the physical and data-link layers are down. While a misconfigured IP address will prevent network access, it is not the first thing to check when a user reports no connectivity.
- ✓
Verify MAC address table and VLAN configuration on the switch.
Why this is correct
This is a valid Layer 2 check, but it is not the first action. Before inspecting the MAC address table or VLAN assignments, you must ensure that physical connectivity exists; if the cable is unplugged or the interface is down, Layer 2 tables cannot populate correctly. Therefore, in the initial troubleshooting sequence, this step comes after verifying Layer 1.
Visual reference
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
Go deeper
Related to this question
Learn chapter
DNS Resolution Process
Key term
DNS
DNS is the system that translates human-friendly domain names like example.com into machine-readable IP addresses so computers can find each other on a network.
Key term
Fully Qualified Domain Name
A Fully Qualified Domain Name is the complete and unambiguous website or server name that includes the host, domain, and top-level domain, leaving no room for guesswork.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.