VLANs (Virtual Local Area Networks) are logical network segments that allow you to group devices together regardless of their physical location. This enables better network management, improved security, and reduced broadcast traffic.
**Creating VLANs:**
To create a VLAN on a Cisco switch, enter gā¦VLANs (Virtual Local Area Networks) are logical network segments that allow you to group devices together regardless of their physical location. This enables better network management, improved security, and reduced broadcast traffic.
**Creating VLANs:**
To create a VLAN on a Cisco switch, enter global configuration mode and use the following commands:
Switch# configure terminal
Switch(config)# vlan 10
Switch(config-vlan)# name Sales
Switch(config-vlan)# exit
This creates VLAN 10 and assigns it the name "Sales."
**Assigning Ports to VLANs:**
To assign a switch port to a specific VLAN, configure the interface as an access port:
Switch(config)# interface fastethernet 0/1
Switch(config-if)# switchport mode access
Switch(config-if)# switchport access vlan 10
**Configuring Trunk Ports:**
Trunk ports carry traffic for multiple VLANs between switches. To configure a trunk:
Switch(config)# interface gigabitethernet 0/1
Switch(config-if)# switchport mode trunk
Switch(config-if)# switchport trunk allowed vlan 10,20,30
**Verification Commands:**
Several commands help verify VLAN configurations:
- show vlan brief: Displays all VLANs and their assigned ports
- show vlan id 10: Shows details for a specific VLAN
- show interfaces trunk: Displays trunk port information
- show interfaces switchport: Shows switchport configuration details
**Native VLAN Configuration:**
The native VLAN handles untagged traffic on trunk links. Configure it using:
Switch(config-if)# switchport trunk native vlan 99
**Best Practices:**
Change the default native VLAN from VLAN 1 for security purposes. Use descriptive VLAN names for easier management. Document your VLAN assignments and ensure consistency across all switches in your network. Regularly verify configurations using show commands to maintain proper network operation and troubleshoot connectivity issues efficiently.
Configure and Verify VLANs - Complete CCNA Guide
Why VLAN Configuration is Important
Virtual Local Area Networks (VLANs) are fundamental to modern network design and are heavily tested on the CCNA exam. Understanding VLAN configuration is essential because VLANs provide logical segmentation of networks, improving security, reducing broadcast traffic, and enabling better network management. In real-world scenarios, nearly every enterprise network uses VLANs to separate departments, secure sensitive data, and optimize network performance.
What is a VLAN?
A VLAN is a logical grouping of network devices that behave as if they are on the same physical network segment, regardless of their actual physical location. Key characteristics include:
- Each VLAN creates a separate broadcast domain - Devices in different VLANs cannot communicate unless routed - VLANs are identified by a number (1-4094) - VLAN 1 is the default VLAN on Cisco switches - VLANs 1002-1005 are reserved for legacy technologies
How VLAN Configuration Works
Creating a VLAN:
Switch(config)# vlan 10 Switch(config-vlan)# name SALES
- show vlan brief - Displays all VLANs and their assigned ports - show vlan id 10 - Shows specific VLAN information - show interfaces trunk - Displays trunk port details and allowed VLANs - show interfaces switchport - Shows switchport configuration details - show running-config interface fa0/1 - Shows interface-specific configuration
Access vs Trunk Ports
Access Ports: Belong to a single VLAN, typically connect to end devices like computers and printers. Traffic is untagged.
Trunk Ports: Carry traffic for multiple VLANs between switches. Traffic is tagged using 802.1Q protocol (except native VLAN traffic).
Native VLAN Considerations
The native VLAN is the VLAN whose traffic traverses a trunk link untagged. By default, this is VLAN 1. For security purposes, it is recommended to: - Change the native VLAN to an unused VLAN - Ensure native VLAN matches on both ends of a trunk - Avoid using VLAN 1 as the native VLAN
Exam Tips: Answering Questions on Configure and Verify VLANs
1. Know the default settings: All ports start in VLAN 1, and the default native VLAN is 1. Questions often test whether you understand default behavior.
2. Memorize verification commands: Be able to identify which command provides specific information. show vlan brief shows VLAN-to-port mappings, while show interfaces trunk shows trunk-specific details.
3. Watch for native VLAN mismatches: Scenario questions may describe connectivity issues caused by mismatched native VLANs on trunk links.
4. Understand the configuration sequence: VLANs must exist before ports can be assigned to them (though Cisco switches will auto-create VLANs).
5. Differentiate between DTP modes: Know that switchport mode access disables trunking, while switchport mode trunk forces trunking.
6. Read outputs carefully: Exam questions often include show command outputs. Look for the administrative mode vs operational mode in switchport outputs.
7. Remember allowed VLAN syntax: Commands like switchport trunk allowed vlan add 50 versus switchport trunk allowed vlan 50 behave differently - the second replaces all allowed VLANs.
8. Practice troubleshooting scenarios: Common issues include ports in wrong VLANs, trunk misconfigurations, and VLANs not being allowed on trunks.