Troubleshooting VLAN and Trunk Problems on Cisco Switches
Most VLAN outages stem from ports in the wrong VLAN, trunks not allowing required VLAN, or native VLAN mismatches. Here's how to diagnose and fix them systematically.
VLAN
Virtual LANs and Layer 2 switching, the foundation of every campus network. Articles tagged VLAN cover fundamentals, trunking, inter-VLAN routing, EtherChannel, troubleshooting, and campus design on Cisco Catalyst switches.
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Private VLANs on Cisco Catalyst Switches: Isolated and Community Ports
Private VLANs let you enforce micro-segmentation within a single VLAN—isolating hosts completely or grouping them into communities while keeping them behind a single gateway IP.
Configuring Voice VLANs on Cisco Switches for IP Phones
Voice VLANs let a single access port carry both data traffic from a PC and voice traffic from an IP phone — each in its own VLAN with its own QoS treatment.
Inter-VLAN Routing on a Layer 3 Switch: SVI-Based Routing on Catalyst 9000
Layer 3 switches route between VLANs in hardware at wire speed — no external router bottleneck. Here is how to configure SVI-based inter-VLAN routing on a Catalyst 9300.
Inter-VLAN Routing with Router-on-a-Stick on Cisco IOS XE
When you don't have a Layer 3 switch, router-on-a-stick provides inter-VLAN routing via a single physical link split into subinterfaces. Learn when this design is appropriate, how to configure subinterfaces, and why it's a bandwidth bottleneck.
DTP (Dynamic Trunking Protocol): How It Works and Why You Should Disable It
DTP lets switches negotiate trunk formation automatically—but this convenience comes with security risks that make disabling it a best practice in production networks.
VLAN Access Ports and Switchport Modes: Access, Trunk, and Dynamic
Learn the differences between access mode, trunk mode, and dynamic trunking protocol negotiation on Cisco Catalyst switches, and why static configuration is the production standard.
How VLANs Work: Tagging, Broadcast Domains, and Frame Forwarding
VLANs are more than a configuration checkbox — they change how every frame is tagged, forwarded, and filtered inside the switch. Here's the mechanics.
What Is a VLAN? Virtual LANs Explained for Network Engineers
VLANs let you carve one physical switch into multiple isolated broadcast domains — without buying more hardware. Here's how they work and why every network uses them.
Understanding Ethernet LAN Fundamentals for CCNA
Master Ethernet LAN fundamentals for your CCNA exam. Learn how IEEE 802.3 defines Layer 1 and Layer 2 operations, Ethernet frames, MAC addressing, and LAN topology for modern switched networks.
Configuring EtherChannel with LACP on Cisco Catalyst Switches
LACP bundles multiple physical links into one logical pipe—doubling or quadrupling bandwidth while keeping STP happy and providing automatic failover.
Configuring 802.1Q Trunks on Cisco Catalyst Switches
Master 802.1Q trunk configuration between Catalyst switches, including VLAN pruning, native VLAN setup, and comprehensive troubleshooting techniques.