VLAN

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.

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.

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.

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.

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 lets switches negotiate trunk formation automatically—but this convenience comes with security risks that make disabling it a best practice in production networks.