VLAN Creation & Troubleshooting: Complete Hands-On Guide with EVE-NG Lab [CCNP ENTERPRISE]

VLAN Creation_Troubleshooting_Complete Hands-On Guide with EVE-NG Lab_[CCNP ENTERPRISE]

Everything seemed easy on paper until the first trunk port failed, and the whole lab collapsed. That’s when I realized: configuring VLANs is one part, troubleshooting them is another beast altogether. In this post, I’ll walk you through VLAN creation, CLI commands, real-world cases, and yes—how to fix them when things go wrong. Whether you’re studying for CCNA, CCNP, or just upgrading your lab skills, you’ll walk away confident and hands-on.


Theory in Brief: Understanding VLANs

A VLAN (Virtual Local Area Network) is a logical segmentation of a switch network, allowing different devices to communicate as if they were in separate physical LANs—even if they’re on the same switch.

VLANs help in improving security, reducing broadcast domains, and enhancing network performance. For example, you can have VLAN 10 for HR, VLAN 20 for Finance, and VLAN 30 for IT, each isolated from the other unless you configure routing between them.

Each VLAN is assigned a unique ID (1-4094). Ports on a switch can be either access ports (belong to a single VLAN) or trunk ports (carry traffic for multiple VLANs using tagging protocols like 802.1Q).

In enterprise environments, VLANs are crucial for user segmentation, VoIP, guest access, and multitenant networks. The separation also helps with policy enforcement, limiting broadcast storms, and applying Quality of Service (QoS) rules more effectively.


VLAN Summary: Comparison & Pros and Cons

Feature/AspectAccess Port VLANTrunk Port VLANProsCons
DescriptionAssigned to one VLANCarries multiple VLANsIsolation, security, better broadcast controlMisconfigurations can cause loss of access
Used inEnd devices (PCs, printers)Switch-to-switch, switch-to-routerScalable design, flexibilityAdds complexity in large networks
VLAN TaggingNo (untagged)Yes (802.1Q tagged)Efficient use of single physical linksNeeds careful planning
TroubleshootingSimple (1 VLAN per port)Requires checking tag configsEasier to isolate issuesTagging errors can cause VLAN mismatches

Essential CLI Commands (Cisco IOS Format)

TaskCLI CommandDescription
View existing VLANsshow vlan briefLists all VLANs on switch
Create VLANvlan 10 + name HRCreates VLAN with ID and name
Assign VLAN to portinterface fa0/1switchport access vlan 10Assigns port to a VLAN
Make port a trunkswitchport mode trunkEnables trunking on port
Check trunk statusshow interfaces trunkLists active trunk ports
Verify VLAN on portshow interface fa0/1 switchportShows port VLAN assignment
Ping test between VLANsping [IP address]Basic reachability test
Troubleshoot STP issuesshow spanning-tree vlan 10STP info per VLAN
Debug VLAN traffic (advanced)debug sw-vlan packetUsed for packet-level issues

Real-World Use Case

ScenarioVLAN SetupBenefit
Office with departments (HR, IT)VLAN 10 = HR, VLAN 20 = IT, VLAN 30 = FinanceDepartment isolation, security
VoIP deploymentVLAN 40 = Voice, separate from data VLANsQoS and jitter control
Guest Wi-Fi with limited accessVLAN 50 = Guest Network, ACL applied to block internal resourcesSecure guest access
School/College networkVLAN per lab/classroom to control access and reduce broadcast trafficControlled student access
Multi-tenant buildingVLANs per company with separate subnets and policiesLogical separation without physical isolation

EVE-NG LAB: Basic VLAN Creation with Troubleshooting

Topology:

  • PC1 = VLAN 10
  • PC2 = VLAN 10
  • Trunk link between SW1 and SW2
  • Ping test from PC1 to PC2

Configuration (Cisco IOS):

SW1

vlan 10
 name HR

interface fa0/1
 switchport mode access
 switchport access vlan 10
 no shutdown

interface fa0/24
 switchport trunk encapsulation dot1q
 switchport mode trunk
 no shutdown

SW2

vlan 10
 name HR

interface fa0/2
 switchport mode access
 switchport access vlan 10
 no shutdown

interface fa0/24
 switchport trunk encapsulation dot1q
 switchport mode trunk
 no shutdown

Test:

PC1> ping PC2_IP

Success = VLAN is configured and trunk is passing tags
Failure = Check VLANs, trunk mode, allowed VLANs, interface status


Troubleshooting Tips

ProblemLikely CauseFix or CLI Command
Devices in same VLAN can’t pingTrunk not configured or mis-taggedshow interfaces trunk + verify VLAN ID
Port not in right VLANWrong access configshow vlan brief + show run int fa0/x
VLAN not showing on switchVLAN not createdvlan <ID> again in config mode
Trunk link downPhysical issue or wrong configshow interface status + cabling check
VLAN blocked by STPSTP blocking portshow spanning-tree vlan <ID>

VLAN FAQs

1. What is a VLAN and why is it used in modern networks?

Answer:
A VLAN (Virtual Local Area Network) logically segments a Layer 2 network into multiple broadcast domains.
Benefits include:

  • Improved security (isolation of departments)
  • Reduced broadcast traffic
  • Efficient traffic management
    Each VLAN behaves as a separate physical LAN, even though all devices may be connected to the same switch.

2. How do I create a VLAN on a Cisco switch using CLI?

Answer:

configure terminal
vlan 10
 name SALES
exit

This creates VLAN 10 and names it “SALES”.
To assign an interface to this VLAN:

interface fa0/1
 switchport mode access
 switchport access vlan 10

3. How do I verify VLAN creation and interface assignments?

Answer:
Use the following commands:

show vlan brief
  • Lists all VLANs and their assigned ports
show interfaces switchport
  • Shows access/trunk status and VLAN assignment of interfaces

4. What are common reasons VLANs fail to communicate across switches?

Answer:

  • Trunk links not configured or misconfigured
  • VLAN not allowed on the trunk
  • Native VLAN mismatch
  • Switchport in the wrong mode (access vs trunk)
  • Missing VLAN on one of the switches

Use:

show interfaces trunk
show cdp neighbors detail

To diagnose such issues.


5. Can VLANs communicate with each other by default?

Answer:
No. VLANs are isolated Layer 2 domains. To allow communication:

  • You need Inter-VLAN Routing, done via:
    • A Layer 3 switch
    • A router-on-a-stick configuration

Example:

interface g0/0.10
 encapsulation dot1Q 10
 ip address 192.168.10.1 255.255.255.0

6. How do I troubleshoot when devices in the same VLAN can’t communicate?

Answer:
Check the following:

  • Interface assigned to correct VLAN:
show interfaces fa0/1 switchport
  • Interface status:
show interfaces fa0/1 status
  • MAC address table:
show mac address-table vlan 10
  • Ping between end devices to test reachability

7. What is the maximum number of VLANs supported on Cisco switches?

Answer:
Standard VLANs:

  • Range: 1–1005
  • VLANs 1, 1002–1005 are reserved and cannot be deleted
    Extended VLANs (1006–4094) are supported in VTP Transparent or VTP Off modes on some switches.

8. How do I ensure VLANs are consistent across all switches in my topology?

Answer:
Options include:

  • Manually creating VLANs on each switch (for smaller networks)
  • Using VTP (VLAN Trunking Protocol) to propagate VLAN info automatically

Verify with:

show vtp status

But be cautious—incorrect VTP configuration can delete VLANs. Back up configs first.


9. How does EVE-NG help with VLAN lab simulation?

Answer:
EVE-NG allows you to:

  • Build multi-switch topologies
  • Simulate access and trunk ports
  • Test VLAN tagging, trunking, and inter-VLAN routing
  • Use real Cisco IOS images for hands-on CLI experience

It’s a perfect platform for CCNP labs and troubleshooting practice.


10. What commands are most helpful when troubleshooting VLANs?

Answer:

CommandPurpose
show vlan briefList VLANs and their assigned ports
show interfaces trunkVerify trunk links and allowed VLANs
show mac address-tableSee learned MACs in VLANs
show interfaces switchportView mode and VLAN of an interface
pingBasic Layer 3 connectivity test
show spanning-tree vlan <id>Check STP role and status of ports

These help narrow down port mode, VLAN mismatch, and connectivity issues.


YouTube Link

Watch the Complete CCNP Enterprise: VLAN Creation & Troubleshooting: Complete Hands-On Guide with EVE-NG Lab Demo & Explanation on our channel:

Class 1 CCNP Enterprise Course and Lab Introduction | FULL COURSE 120+ HRS | Trained by Sagar Dhawan
Class 2 CCNP Enterprise: Packet Flow in Switch vs Router, Discussion on Control, Data and Management
Class 3 Discussion on Various Network Device Components
Class 4 Traditional Network Topology vs SD Access Simplified

Final Note

Understanding how to differentiate and implement VLAN Creation & Troubleshooting: Complete Hands-On Guide with EVE-NG Lab is critical for anyone pursuing CCNP Enterprise (ENCOR) certification or working in enterprise network roles. Use this guide in your practice labs, real-world projects, and interviews to show a solid grasp of architectural planning and CLI-level configuration skills.

If you found this article helpful and want to take your skills to the next level, I invite you to join my Instructor-Led Weekend Batch for:

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