CCNA Switching and Network Access Practice Question
A host is physically connected to switch port Gi0/3. The technician runs 'show mac address-table' but does not find the host's MAC address for Gi0/3. The port status shows 'up/up', and the host was connected only a few minutes ago. What should the technician do next?
⚠ Common exam trap
Cisco often tests the misconception that a missing MAC address is due to STP blocking or a stale table, when in fact the port being 'up/up' and recently connected makes VLAN misconfiguration the most logical first step to troubleshoot.
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
✓
Verify the VLAN assignment on Gi0/3 using 'show vlan brief' or 'show interfaces Gi0/3 switchport'.
The most likely reason a newly connected host's MAC address does not appear in the MAC address table is that the switch port is in the wrong VLAN or is administratively configured as an access port in a VLAN that does not match the host's expected VLAN. The 'show vlan brief' command verifies VLAN existence and port membership, while 'show interfaces Gi0/3 switchport' confirms the operational VLAN assignment. Since the port is up/up and the host was connected only minutes ago, the switch should have learned the MAC address via normal flooding; its absence points to a VLAN mismatch or port configuration issue, not a stale table or STP blocking.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Clear the MAC address table with 'clear mac address-table dynamic' to force immediate relearning.
Why it's wrong here
The default MAC aging time is 300 seconds, so aging is not the issue for a recently connected host. Clearing the table does not fix an underlying VLAN misconfiguration and would result in the MAC being learned again in the wrong VLAN.
- ✓
Verify the VLAN assignment on Gi0/3 using 'show vlan brief' or 'show interfaces Gi0/3 switchport'.
Why this is correct
The switch learns MAC addresses per VLAN. If Gi0/3 is in an unexpected VLAN, the MAC address will be learned in that VLAN's table and not visible in the default or expected VLAN view. Checking the VLAN membership directly confirms whether the host is in the correct Layer 2 broadcast domain.
- ✗
Check the STP state of Gi0/3 with 'show spanning-tree interface Gi0/3' to ensure it is not blocking.
Why it's wrong here
Although a port in STP blocking state does not learn MAC addresses, an access port facing a single host normally transitions to forwarding quickly and is unlikely to be blocking after being connected for several minutes without a topology change. VLAN assignment should be verified first.
- ✗
Inspect the ARP cache with 'show ip arp' to check for duplicate IP addresses.
Why it's wrong here
The ARP cache maps IP addresses to MAC addresses at Layer 3. The MAC address table is a Layer 2 function and will learn the host's MAC regardless of any IP addressing issues. A duplicate IP does not prevent MAC learning.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Verify the VLAN assignment on Gi0/3 using 'show vlan brief' or 'show interfaces Gi0/3 switchport'.Correct answer▾
Why this is correct
The switch learns MAC addresses per VLAN. If Gi0/3 is in an unexpected VLAN, the MAC address will be learned in that VLAN's table and not visible in the default or expected VLAN view. Checking the VLAN membership directly confirms whether the host is in the correct Layer 2 broadcast domain.
✗Clear the MAC address table with 'clear mac address-table dynamic' to force immediate relearning.Wrong answer — click to see why▾
Why this is wrong here
This is a drastic action that does not address a VLAN mismatch; the same symptom would recur.
✗Check the STP state of Gi0/3 with 'show spanning-tree interface Gi0/3' to ensure it is not blocking.Wrong answer — click to see why▾
Why this is wrong here
Jumping to STP before confirming basic Layer 2 VLAN membership is not the most efficient next step.
✗Inspect the ARP cache with 'show ip arp' to check for duplicate IP addresses.Wrong answer — click to see why▾
Why this is wrong here
This option confuses Layer 2 MAC learning with Layer 3 ARP resolution, and does not help locate the MAC entry in the address table.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
Go deeper
Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
MAC address
A MAC address is a unique hardware identifier assigned to a network interface card that allows devices to communicate on a local network.
Key term
STP
Shielded Twisted Pair (STP) is a copper cable that wraps each twisted pair in foil or braid to block electromagnetic interference.
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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.