Listen to this Post
Virtual LANs (VLANs) are crucial for segmenting networks, enhancing security, and improving network efficiency. In this setup, VLAN 20 is created and assigned to a specific port on the switch.
Creating VLAN 20:
- Define the VLAN and give it a meaningful name (e.g., IT Department).
- Exit configuration mode after setup.
Assigning VLAN to a Port:
- Select the desired interface (e.g., GigabitEthernet 0/1).
- Set it as an access port to allow a single VLAN.
- Assign it to VLAN 20 for proper traffic segmentation.
VLANs help reduce network congestion, enhance security, and enable better traffic management. A must-know for any networking professional!
You Should Know:
Cisco Switch VLAN Configuration Commands:
Enter privileged EXEC mode enable Enter global configuration mode configure terminal Create VLAN 20 with name vlan 20 name IT_Department exit Assign interface to VLAN 20 interface gigabitethernet 0/1 switchport mode access switchport access vlan 20 no shutdown exit
VTP (VLAN Trunking Protocol) Configuration:
Configure VTP domain vtp domain yourdomainname vtp mode client vtp password yourpassword exit
Useful VLAN Verification Commands:
Show all VLANs show vlan brief Show interface status show interfaces status Show MAC address table show mac-address-table Find device port by MAC show mac-address-table address aaaa.bbbb.cccc
Linux VLAN Configuration:
Create VLAN interface sudo vconfig add eth0 20 Bring VLAN interface up sudo ifconfig eth0.20 up Assign IP to VLAN interface sudo ifconfig eth0.20 192.168.20.1 netmask 255.255.255.0 Persistent VLAN configuration (Debian/Ubuntu) Add to /etc/network/interfaces: auto eth0.20 iface eth0.20 inet static address 192.168.20.1 netmask 255.255.255.0 vlan-raw-device eth0
Windows VLAN Configuration:
Check network interfaces Get-NetAdapter Enable VLAN identification (requires NIC driver support) Set-NetAdapterAdvancedProperty -Name "Ethernet" -DisplayName "VLAN ID" -DisplayValue "20"
Trunk Port Configuration (Between Switches):
interface gigabitethernet 0/24 switchport mode trunk switchport trunk allowed vlan 10,20,30 switchport trunk native vlan 99 no shutdown exit
Packet Capture for VLAN Traffic:
Linux (capture VLAN tagged traffic) sudo tcpdump -i eth0 -nn -e vlan Cisco (SPAN port configuration) monitor session 1 source interface gigabitethernet 0/1 monitor session 1 destination interface gigabitethernet 0/24
VLAN Security Best Practices:
- Always change default VLAN 1 to another unused VLAN
2. Use private VLANs for sensitive devices
3. Implement VLAN access control lists (VACLs)
- Disable unused switch ports and assign them to a “dead” VLAN
What Undercode Say:
VLANs remain a fundamental technology in network segmentation and security. The ability to logically separate networks while maintaining physical infrastructure is powerful. Beyond basic configuration, mastering VLANs involves understanding trunking protocols, VTP domains, and inter-VLAN routing.
For deeper implementation, consider these advanced commands:
Inter-VLAN routing configuration
interface vlan 20
ip address 192.168.20.1 255.255.255.0
no shutdown
exit
Show VLAN trunking protocol status
show vtp status
Clear VLAN statistics
clear vlan statistics
Linux VLAN filtering with bridge
sudo ip link add link eth0 name eth0.20 type vlan id 20
sudo ip addr add 192.168.20.2/24 dev eth0.20
sudo ip link set dev eth0.20 up
Windows PowerShell VLAN check
Get-NetAdapter | Where-Object {$_.VlanID -ne $null} | Select Name, VlanID
Remember that VLANs are only as secure as their implementation. Always combine VLAN segmentation with other security measures like port security, 802.1X authentication, and proper firewall rules between VLANs.
Expected Output:
Properly configured VLANs will show in `show vlan brief` output with correct port assignments. Trunk ports will display allowed VLANs in show interfaces trunk. Inter-VLAN routing requires Layer 3 switch configuration or router-on-a-stick setup. Monitoring tools should show reduced broadcast traffic and proper segmentation between VLANs.
References:
Reported By: Nasir Amin – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
