What is SVI? Difference Between SVI and VLAN Explained

Introduction

If you have worked with Cisco switches, you have likely come across the terms VLAN and SVI. While they sound similar and are closely related, they serve completely different purposes. Confusing the two is one of the most common mistakes made by networking students and even junior engineers.

In simple terms: a VLAN is a logical network segment that groups ports together, while an SVI (Switched Virtual Interface) is a virtual Layer 3 interface that provides IP connectivity to that VLAN. Think of a VLAN as a room and the SVI as the door that lets traffic in and out of it. This article explains both concepts clearly, highlights their differences, and shows you how they work together in real Cisco network designs.

What is a VLAN?

A Virtual Local Area Network (VLAN) is a logical grouping of switch ports that behave as if they are on the same physical network, regardless of their actual physical location. VLANs operate at Layer 2 (Data Link Layer) of the OSI model.

How VLANs Work

When a switch port is assigned to a VLAN, frames sent from that port are tagged with a VLAN ID (1–4094 as per IEEE 802.1Q). The switch uses these tags to keep traffic from different VLANs completely isolated from one another, even though they share the same physical switch hardware.

What a VLAN Does

• Segments a network into isolated broadcast domains
• Improves security by keeping traffic separated
• Reduces unnecessary broadcast traffic
• Logically groups users by department or function (e.g., HR, Finance, IT)
• Operates at Layer 2 — no IP address assigned to the VLAN itself

What is an SVI (Switched Virtual Interface)?

A Switched Virtual Interface (SVI) is a virtual Layer 3 interface created on a multilayer (Layer 3) switch and associated with a specific VLAN. It is essentially the switch's logical IP interface for that VLAN.

When you assign an IP address to an SVI, you give the switch the ability to route traffic into and out of that VLAN. The SVI acts as the default gateway for all devices in its associated VLAN.

SVI in Action — Inter-VLAN Routing

In the diagram above, PC-A (VLAN 10) sends a packet to PC-B (VLAN 20). The packet is handed up to the SVI for VLAN 10, routed internally to the SVI for VLAN 20, and forwarded down to PC-B — all within the same Layer 3 switch. No external router is needed.

SVI Configuration Example

! Create VLAN 10 first
Switch# configure terminal
Switch(config)# vlan 10
Switch(config-vlan)# name HR_Network
Switch(config-vlan)# exit

! Create SVI for VLAN 10 and assign IP address
Switch(config)# interface vlan 10
Switch(config-if)# description Gateway for HR VLAN
Switch(config-if)# ip address 192.168.10.1 255.255.255.0
Switch(config-if)# no shutdown
Switch(config-if)# exit

! Enable IP routing on the Layer 3 switch
Switch(config)# ip routing

This is Test Code

Uses of SVI

• Inter-VLAN Routing: Routes traffic between VLANs without an external router
• Default Gateway: Acts as the gateway for all devices in the VLAN
• Switch Management: Used to assign a management IP to access the switch remotely via SSH/Telnet
• DHCP Helper: Configured with ip helper-address to forward DHCP requests to a central server
• HSRP/VRRP: Used in redundancy protocols to provide a virtual gateway IP

Difference Between SVI and VLAN

Although SVI and VLAN are tightly linked, they are fundamentally different constructs. The table below captures every key difference:

How VLAN and SVI Work Together

VLAN and SVI are complementary — a VLAN provides the Layer 2 broadcast domain, and the SVI provides the Layer 3 IP gateway into that domain. Neither replaces the other; you need both for full network functionality.

The Relationship — A Simple Rule

Understanding SVI Status

When you run show interfaces vlan <id>, the SVI can be in one of several states. Understanding these states is critical for troubleshooting.

! Verify SVI status
Switch# show interfaces vlan 10
Switch# show ip interface brief
Switch# show vlan brief

! Management SVI on a Layer 2 switch (Catalyst 2960)
Switch(config)# vlan 99
Switch(config-vlan)# name Management
Switch(config-vlan)# exit

Switch(config)# interface vlan 99
Switch(config-if)# ip address 10.0.99.10 255.255.255.0
Switch(config-if)# no shutdown
Switch(config-if)# exit

! Set default gateway for management traffic
Switch(config)# ip default-gateway 10.0.99.1