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.
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Latest posts — page 57
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.
Cisco Switchport Modes: Access, Trunk and Dynamic (DTP)
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.
BGP Path Attributes Explained: Well-Known vs Optional
BGP path attributes are the foundation of every traffic engineering technique: local preference, MED, AS-path prepending, communities. Understand the well-known vs optional attribute matrix before touching policy.
BGP Message Types: OPEN, UPDATE, KEEPALIVE, and NOTIFICATION
BGP uses just four message types: OPEN, UPDATE, KEEPALIVE, and NOTIFICATION. Understanding the field-level format of each makes debug output and packet captures far more readable for anyone troubleshooting BGP.
eBGP vs iBGP: What's the Difference and When to Use Each
eBGP and iBGP look similar at a glance but behave very differently around TTL, next-hop, AS-path, and route advertisement. Treating them as the same protocol gets you in trouble fast; here are the rules.