Networking

SVI (Switch Virtual Interface)

Added: June 27, 2026Nurtured: July 13, 2026

Definition

SVI (Switch Virtual Interface) is a virtual Layer 3 interface created for a VLAN on a Layer 3 switch. Its role is to give a VLAN an IP address so the switch can communicate with devices in that VLAN and route traffic between different VLANs.

What Problem It Solves

A Layer 2 switch can only forward frames inside the same VLAN. If VLAN 10 wants to talk to VLAN 20, it cannot. An SVI allows each VLAN to have its own gateway IP, enabling the Layer 3 switch to perform inter-VLAN routing without needing an external router.

What Happens If Not Used

Devices in the same VLAN can still communicate.
Devices in different VLANs cannot communicate.
You would need a separate router (Router-on-a-Stick) for inter-VLAN routing.

Easy Wording

An SVI is the "gateway" of a VLAN inside a Layer 3 switch.

Layman Example

Imagine a building with separate departments (VLANs). Each department has its own receptionist (SVI). When someone wants to contact another department, they first go to their receptionist, who forwards them correctly.

Technical Example

Without SVI

PC-A (VLAN 10) │ Layer 2 Switch │ Cannot reach VLAN 20 ❌

With SVI

PC-A │ VLAN 10 │ SVI VLAN10 (192.168.10.1) │ Layer 3 Switch (Routes) │ SVI VLAN20 (192.168.20.1) │ VLAN 20 │ PC-B

Request Flow

PC-A sends traffic to PC-B (different subnet).
PC-A sends it to its default gateway: SVI VLAN 10.
The Layer 3 switch routes the packet.
It forwards it through SVI VLAN 20.
PC-B receives the packet.

Limitation

An SVI only routes between VLANs on the same Layer 3 switch. It does not automatically allow communication with other networks (Internet, remote offices, or other LANs).