Inter-VLAN Routing

Learning objectives

• Explain the purpose and scope of Inter-VLAN Routing.
• Identify important protocols, roles, fields, and terminology.
• Apply the concept to a practical network scenario.
• Use IOS XE commands to verify operational behavior.

1. Core concepts

Each VLAN is a separate Layer 2 broadcast domain and usually maps to a different IP subnet. A host sending to another subnet forwards the packet to its default gateway. That gateway routes the packet into the destination VLAN.

2. How it works

Router-on-a-stick uses one physical router interface with multiple logical subinterfaces. Each subinterface uses 802.1Q encapsulation and an IP address for its VLAN. A multilayer switch can instead use an SVI (interface vlan X) as the gateway and route in hardware. Enable ip routing on platforms that require it.

Visual walkthrough

3. Worked example

VLAN 10 uses 192.168.10.0/24 with gateway .1. VLAN 20 uses 192.168.20.0/24 with gateway .1. Router subinterfaces Gi0/0/0.10 and .20 use encapsulation dot1q 10 and 20. The switch-to-router link must be a trunk.

IOS XE commands and verification

Syntax and feature availability can vary by device family and software release. Confirm platform support before applying configuration.

interface gi0/0/0.10
 encapsulation dot1Q 10
 ip address 192.168.10.1 255.255.255.0
interface gi0/0/0.20
 encapsulation dot1Q 20
 ip address 192.168.20.1 255.255.255.0
ip routing
interface vlan 10
 ip address 192.168.10.1 255.255.255.0
show ip interface brief

Common mistakes and troubleshooting

• Check physical and interface state before changing higher-layer settings.
• Verify both ends agree on addressing, VLAN, encapsulation, and protocol parameters.
• Use operational show commands; configured text alone does not prove a feature is working.
• Change one variable at a time and verify the result.

Knowledge check

Choose one answer per question. Submit to see why the correct choice is right and why every other option is wrong. These are original practice questions, not Cisco exam questions.