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.

36 posts

VLAN

VLAN, Subnet, and Broadcast Domain: What's the Difference?

VLAN, subnet, and broadcast domain are not the same thing. The layer each lives at, the relationships between them, and the misalignment that breaks hosts silently.

May 20, 2026 5 min read

VLAN

Tagged vs Untagged VLANs: How Trunks and Access Ports Really Work

Tagged and untagged frames are the half of every VLAN problem nobody explains clearly. The mental model, when each is correct, the native VLAN, and the cross-vendor (Cisco / Aruba / Juniper) cheat sheet.

Apr 25, 2026 7 min read

VLAN

VLAN Hopping Attacks Explained: Switch Spoofing and Double Tagging

VLAN hopping bypasses Layer 2 isolation. The two attacks (switch spoofing via DTP, double tagging via the native VLAN) and the four-line Cisco configuration that defeats both.

Apr 25, 2026 7 min read

VLAN

802.1Q VLAN Tag Explained: The 4 Bytes That Make Trunking Work

The 802.1Q VLAN tag is 4 bytes inserted into Ethernet frames to carry VLAN identity across trunks. TPID, TCI, PCP, DEI, VID, and the native VLAN explained byte by byte.

Apr 25, 2026 7 min read

VLAN

VLAN Design for Campus Networks: From Access to Core

A good VLAN design scales cleanly, keeps STP domains small, and makes troubleshooting obvious. Here is how to plan VLANs for a multi-building campus network.

Apr 1, 2026 8 min read

VLAN

VLAN Security Hardening: Protecting Your Layer 2 Network

VLANs provide segmentation, not security. Without explicit hardening — disabling DTP, fixing the native VLAN, enabling DHCP snooping and DAI — your Layer 2 network is wide open to attack.

Apr 1, 2026 7 min read