What is it?
Router-on-a-Stick routes multiple VLANs through one physical router link by using 802.1Q subinterfaces.
Why should I learn it?
It is the simplest inter-VLAN routing design to reason about before moving to SVIs or Layer-3 switching.
How it works
Switch tags VLAN traffic on a trunk → router subinterface matches the VLAN tag → router routes between subinterfaces.
Real-world example
SW1 sends tagged VLAN 10 traffic over a trunk to R1 E0/0.10. R1 routes it and can return traffic through E0/0.20 for VLAN 20. Each subinterface acts as that VLAN’s gateway.
Troubleshooting mindset
Compare access VLAN → trunk → dot1q VLAN ID → subinterface IP → host gateway.
Common mistake
Do not memorise the definition without connecting it to packet flow, device state and verification. Ask: what should happen, what actually happened, and which command or capture can prove the difference?
Quick recap
- Understand the job of the protocol or feature.
- Know where it sits in the traffic path.
- Verify behaviour instead of guessing.
- Connect the topic to the next networking layer.
Interview connection
Explain the concept in simple words first. Then give one practical example or troubleshooting check. That is stronger than repeating a textbook definition.
References & Further Reading
- How to Master CCNA — supplied reference material.
- CCNA Notes — supplied technical/configuration reference.
Apni Bhasha mein samjho
Ek physical router interface par multiple subinterfaces bana kar multiple VLANs ko gateway de sakte ho. Switch-router link trunk hota hai.
Kaise padho?
Concept ko pehle flow ke saath samjho. Phir English note ke technical terms, commands aur tables dekho — technical terminology same rahegi.