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.

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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.

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VLAN Summary: Comparison & Pros and Cons

Feature/Aspect	Access Port VLAN	Trunk Port VLAN	Pros	Cons
Description	Assigned to one VLAN	Carries multiple VLANs	Isolation, security, better broadcast control	Misconfigurations can cause loss of access
Used in	End devices (PCs, printers)	Switch-to-switch, switch-to-router	Scalable design, flexibility	Adds complexity in large networks
VLAN Tagging	No (untagged)	Yes (802.1Q tagged)	Efficient use of single physical links	Needs careful planning
Troubleshooting	Simple (1 VLAN per port)	Requires checking tag configs	Easier to isolate issues	Tagging errors can cause VLAN mismatches

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Essential CLI Commands (Cisco IOS Format)

Task	CLI Command	Description
View existing VLANs	show vlan brief	Lists all VLANs on switch
Create VLAN	vlan 10 + name HR	Creates VLAN with ID and name
Assign VLAN to port	interface fa0/1 → switchport access vlan 10	Assigns port to a VLAN
Make port a trunk	switchport mode trunk	Enables trunking on port
Check trunk status	show interfaces trunk	Lists active trunk ports
Verify VLAN on port	show interface fa0/1 switchport	Shows port VLAN assignment
Ping test between VLANs	ping [IP address]	Basic reachability test
Troubleshoot STP issues	show spanning-tree vlan 10	STP info per VLAN
Debug VLAN traffic (advanced)	debug sw-vlan packet	Used for packet-level issues

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Real-World Use Case

Scenario	VLAN Setup	Benefit
Office with departments (HR, IT)	VLAN 10 = HR, VLAN 20 = IT, VLAN 30 = Finance	Department isolation, security
VoIP deployment	VLAN 40 = Voice, separate from data VLANs	QoS and jitter control
Guest Wi-Fi with limited access	VLAN 50 = Guest Network, ACL applied to block internal resources	Secure guest access
School/College network	VLAN per lab/classroom to control access and reduce broadcast traffic	Controlled student access
Multi-tenant building	VLANs per company with separate subnets and policies	Logical separation without physical isolation

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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

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Troubleshooting Tips

Problem	Likely Cause	Fix or CLI Command
Devices in same VLAN can’t ping	Trunk not configured or mis-tagged	show interfaces trunk + verify VLAN ID
Port not in right VLAN	Wrong access config	show vlan brief + show run int fa0/x
VLAN not showing on switch	VLAN not created	vlan <ID> again in config mode
Trunk link down	Physical issue or wrong config	show interface status + cabling check
VLAN blocked by STP	STP blocking port	show spanning-tree vlan <ID>

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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.

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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

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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

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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.

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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

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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

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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.

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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.

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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.

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10. What commands are most helpful when troubleshooting VLANs?

Answer:

Command	Purpose
show vlan brief	List VLANs and their assigned ports
show interfaces trunk	Verify trunk links and allowed VLANs
show mac address-table	See learned MACs in VLANs
show interfaces switchport	View mode and VLAN of an interface
ping	Basic 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.

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YouTube Link

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

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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.

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