dot1Q Subinterfaces: The Router Side

Bundle lab · $29.99

Practice creating 802.1Q subinterfaces on a single router uplink to deliver inter-VLAN routing using router-on-a-stick. The Layer-2 switch is already fully configured with VLAN 10 and VLAN 20, access ports for two hosts, and a working 802.1Q trunk to the router. Your job: leave the router's physical Ethernet0/0 unnumbered and add exactly two subinterfaces with the correct encapsulation tags and gateway IPs so hosts can reach their gateways and each other.

Learning objectives

• Configure router-on-a-stick subinterfaces that each carry their own VLAN tag on a single physical interface.
• Keep the physical uplink unnumbered and enabled; place the gateway IPs on subinterfaces only.
• Align encapsulation tags with VLAN IDs and understand how a mismatched or missing tag breaks reachability.
• Verify inter-VLAN routing from hosts and with IOS show commands on both router and switch.

Troubleshooting focus

• Identify and correct encapsulation tag mismatches (e.g., a subinterface's VLAN tag not equal to its VLAN ID).
• Detect missing subinterfaces that leave a VLAN without a routed gateway.
• Confirm that the physical parent interface is up, carries no IP address of its own, and is not otherwise misconfigured.
• Differentiate switch-side issues from router-side configuration, using targeted show commands.