N Is For Networking N4N041: Switched Virtual Interface (SVI) and Integrated Routing and Bridging (IRB)
Oct 23, 2025
Dive into the intriguing world of Switched Virtual Interfaces (SVI) and Integrated Routing and Bridging (IRB)! The hosts unravel the confusion around these terms and explore their historical evolution. Learn how early VLAN routing worked and why the 'router on a stick' method was inefficient. Discover the real role of SVIs and IRBs as vital IP endpoints for local routing. Plus, the discussion extends to their applications beyond just default gateways, touching on modern networking patterns and encapsulations!
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SVI And IRB Are Functionally The Same
- SVI and IRB are essentially the same concept across vendors, serving as virtual layer-3 interfaces tied to VLANs.
- Historical vendor terms differ, but functionally they let a switch act as a gateway for a VLAN.
Why Router-On-A-Stick Existed
- VLANs split a switch into multiple broadcast domains and need routing to communicate between them.
- Router-on-a-stick used subinterfaces and 802.1Q trunks to route between VLANs before layer-3 switches.
Walk Frames Step-By-Step In A Lab
- Trace frames step-by-step: note source/destination MACs and VLAN tags as packets move between hosts and routers.
- Use a lab and packet captures to confirm how MACs and rewrites change during routing.
