Troubleshooting Scenario: Trunk Link & Inter-VLAN Routing Failure

What are Trunking and Inter-VLAN Routing?

Trunking is a network standard (IEEE 802.1Q) that allows a single physical link between network devices (such as switches or routers) to carry traffic for multiple VLANs by adding a unique tag to each frame. Inter-VLAN Routing is the process of forwarding network traffic between distinct Layer 3 subnets and logical VLANs, typically handled by a Router or a Layer 3 Switch.

Why Use Trunking & Inter-VLAN Routing?

• Link Consolidation: Eliminates the requirement for dedicated physical links for every single VLAN, drastically reducing hardware and cabling costs.
• Cross-VLAN Communication: Enables secure communication across isolated departments (e.g., Accounts reaching Data Center services) under controlled routing policies.
• Scalability: Easily allows VLAN structures to stretch seamlessly across multiple switches throughout an enterprise topology.
• Optimized Traffic Management: Maintains logical broadcast domain separation while enabling inter-subnet connectivity via Layer 3 routing.

Where to Implement Trunking & Inter-VLAN Routing?

• Switch-to-Switch Uplinks: Connecting Access switches to Distribution/Core switches carrying multi-department traffic.
• Switch-to-Router Uplinks (Router-on-a-Stick): Passing tagged multi-VLAN traffic over sub-interfaces to an external router for inter-subnet routing.
• Data Center Connections: Transporting diverse server networks over redundant high-speed links to core routing infrastructure.
• Hypervisor Environment (Virtualization): Linking physical switch interfaces to virtual switches (vSwitches) to host diverse virtual machines.