Inter-VLAN Routing using Multilayer Switch (MLS)
A Multilayer Switch (MLS) can perform both Layer 2 switching and Layer 3 routing. This eliminates
the need for an external router in inter-VLAN communication. The MLS routes traffic internally
between VLANs using Switch Virtual Interfaces (SVIs).
Example VLAN Setup:
VLAN 10 — 192.168.10.0/24 (Gateway: 192.168.10.1)
VLAN 20 — 192.168.20.0/24 (Gateway: 192.168.20.1)
Configuration Example (Cisco):
Switch(config)# interface vlan 10 Switch(config-if)# ip address 192.168.10.1 255.255.255.0
Switch(config-if)# no shutdown Switch(config)# interface vlan 20 Switch(config-if)# ip address
192.168.20.1 255.255.255.0 Switch(config-if)# no shutdown Switch(config)# ip routing
Data Flow Between VLANs:
If PC1 in VLAN 10 sends data to PC3 in VLAN 20:
1. PC1 forwards the packet to its gateway (192.168.10.1) — the SVI on the switch.
2. The MLS routes it internally from VLAN 10 to VLAN 20.
3. The frame is delivered only to PC3 (not all ports in VLAN 20).
Only broadcast or unknown traffic floods the VLAN.
Summary:
- Each device has its own IP; SVI IP is only the gateway.
- MLS sends routed packets only to the destination port.
- Broadcasts/unknown MACs are flooded within the VLAN.
- Routing happens inside the switch — no router required.
Diagram: