A network technician is configuring inter-VLAN routing on a Layer 3 switch. The switch has multiple VLANs (VLAN 10, VLAN 20, VLAN 30) and needs to route traffic between them. Which routing concept is fundamentally being applied when the switch routes packets from a host in VLAN 10 to a host in VLAN 20?
- AStatic route lookup
- BDefault route application
- CDynamic route advertisement
- DDirectly connected route lookup
Show answer & explanationAnswer & explanation
Correct answer: D. Directly connected route lookup
When a Layer 3 switch performs inter-VLAN routing, it has an SVI (Switch Virtual Interface) for each VLAN, configured with an IP address. These SVIs are considered directly connected networks in the switch's routing table. When traffic from VLAN 10 (e.g., 192.168.10.0/24) needs to reach VLAN 20 (e.g., 192.168.20.0/24), the switch performs a lookup for the destination network (192.168.20.0/24). Since VLAN 20 is directly connected via its SVI, the switch uses the directly connected route to forward the packet.
Why the other options are wrong
- A. Static routes are manually configured for networks not directly connected, which isn't the case for inter-VLAN routing on the same switch.
- B. A default route is used for destinations not found in the routing table, typically for outbound internet access, not for routing between directly connected VLANs.
- C. Dynamic routing protocols would advertise these networks, but the fundamental *lookup* is still for a directly connected network from the switch's perspective.
Inter-VLAN Routing with SVIs
Inter-VLAN routing on a Layer 3 switch uses Switch Virtual Interfaces (SVIs), which are logical Layer 3 interfaces associated with VLANs, allowing the switch to route traffic between these directly connected VLAN networks.
- Each SVI acts as the default gateway for its respective VLAN.
- SVIs are treated as directly connected networks in the routing table.
- Enables communication between devices in different VLANs on the same switch.
Memory trick: Each VLAN is a room, the switch is the hallway, and SVIs are the doors.