2.2 Given a scenario, configure switching technologies and features

VLAN

📘CompTIA Network+ (N10-009)

What Is a Switch Virtual Interface (SVI)?

A Switch Virtual Interface (SVI) is a virtual Layer 3 interface created on a switch for a VLAN.
It allows the switch to:

Have an IP address inside that VLAN
Communicate with devices in that VLAN
Perform inter-VLAN routing (if the switch supports Layer 3 routing)
Provide remote management access (SSH, Telnet, WebGUI)

In simple terms:

An SVI gives a VLAN an IP address and allows the switch to participate in that VLAN as if it had a “virtual port” inside it.

Why Are SVIs Important? (Exam Focus)

SVIs are required for several key functions that appear in Network+ exam questions:

1. Remote Management of a Switch

A switch needs an IP address so administrators can connect to it.
This IP address is almost always configured on an SVI, typically the VLAN 1 SVI or a dedicated management VLAN.

2. Inter-VLAN Routing (Layer 3 Switches Only)

A Layer 2 switch cannot route between VLANs.
A Layer 3 switch can route between VLANs using SVIs.

Each VLAN needs its own SVI to act as the default gateway for devices in that VLAN.

3. Logical Interface for Network Services

SVIs can be used by the switch for:

DHCP relay
Routing protocols
Diagnostics (ping, traceroute)

4. Simplifies Management

Instead of creating a physical routed port for each VLAN, the switch uses a virtual interface that does not require actual hardware ports.

Key Functions of SVIs

1. Management Interface

Example in IT:
Admins connecting via SSH to configure the switch must connect to an IP address—this IP lives on an SVI.

Example:

interface vlan 10
 ip address 10.10.10.2 255.255.255.0
 no shutdown

This creates an SVI for VLAN 10 with an IP address.

2. Default Gateway for VLANs (Layer 3 Switch)

Every VLAN needs a default gateway.
With an SVI, the switch provides that gateway.

Example in IT:

VLAN 20 = Finance
SVI for VLAN 20 = 192.168.20.1
All devices in VLAN 20 use 192.168.20.1 as their default gateway.

3. Inter-VLAN Routing

If a Layer 3 switch has SVIs for multiple VLANs, it can route traffic between them internally at high speed.

Example:

SVI VLAN 10: 10.1.10.1
SVI VLAN 20: 10.1.20.1
The switch can route between the two networks without needing a router.

This is known as a multilayer switch.

When Do SVIs Work? (Requirements)

Requirement	Does It Apply to SVI?	Explanation
VLAN must exist	✔️	The VLAN must be created first.
SVI must be administratively up	✔️	`no shutdown` must be applied.
VLAN must be active on at least one physical port	✔️	Otherwise the SVI stays down/down.
Switch must support Layer 3 routing for inter-VLAN routing	✔️ (Layer 3 only)	Layer 2 switches can create SVIs only for management.

SVI States (Exam-Relevant)

SVIs have common interface states just like physical interfaces:

1. Up/Up

VLAN exists
Ports assigned to VLAN are active
SVI is administratively enabled
→ Fully operational

2. Down/Down

Common reasons:

VLAN does not exist
VLAN has no active ports
SVI is shutdown

3. Administratively Down

Interface is manually disabled via shutdown

These states appear frequently in troubleshooting exam questions.

Benefits of Using SVIs

Benefit	Explanation
Centralized management	The switch can be managed from any connected VLAN.
No physical interface required	Virtual, not limited by physical hardware.
Efficient routing inside the switch	Avoids external routers for inter-VLAN routing.
Simple to configure	Only requires VLAN creation + IP assignment.

Common Exam Scenarios

Scenario 1: Cannot Access Switch via SSH

Possible exam answers:

SVI is shutdown
Wrong VLAN used
Wrong IP address on SVI
No active ports in that VLAN
Management VLAN mis-configured

Scenario 2: Inter-VLAN Routing Not Working

Possible correct choices:

Routing is disabled (ip routing missing)
SVI missing for one of the VLANs
SVI is down/down
VLAN not assigned to any port

Scenario 3: Need to Configure Remote Management

Correct steps:

Create Management VLAN
Create SVI
Assign IP
Enable interface
Assign ports to the management VLAN
Configure default gateway (for Layer 2 switches)

SVI Configuration (Cisco-Style)

(Network+ exam is vendor-neutral, but Cisco syntax is widely understood.)

1. Create SVI

interface vlan 20
 ip address 192.168.20.1 255.255.255.0
 no shutdown

2. Enable Routing (Layer 3 Switch)

ip routing

3. Assign Ports to VLAN 20

interface fastEthernet0/3
 switchport mode access
 switchport access vlan 20

Layer 2 vs Layer 3 Switch SVI Capabilities

Feature	Layer 2 Switch	Layer 3 Switch
SVI for management	✔️	✔️
SVI for routing	❌	✔️
Default gateway assignment	Required	Not required (switch routes internally)
Routing protocols	❌	✔️

IT Use Cases (No Real-Life Analogies)

1. Management VLAN

Admins connect to the switch via SSH using the SVI IP address.

2. Data Center VLAN Gateway

Servers inside a VLAN use the SVI as their default gateway.

3. Internal Routing Between Departments

A Layer 3 switch uses multiple SVIs to route between department VLANs (IT, HR, Finance).

What You Need to Know for the Exam

Definition: SVI is a virtual Layer 3 interface for a VLAN.
Purpose: Management + inter-VLAN routing.
Layer 2 switches → SVI for management only.
Layer 3 switches → SVI provides routing.
Each VLAN that needs routing must have its own SVI.
SVI must be up (VLAN active and no shutdown).
SVI provides the default gateway for the VLAN.
Requires IP routing enabled on multilayer switches.

These points frequently appear in Network+ multiple-choice and scenario questions.

Final Summary

A Switch Virtual Interface (SVI) is a virtual interface on a switch used to provide an IP address to a VLAN.
It enables:

Remote management
Routing between VLANs (on Layer 3 switches)
Gateway services per VLAN
Logical IP-based communication inside switching environments

Understanding how SVIs work, how to configure them, and how to troubleshoot them is essential for passing the CompTIA Network+ (N10-009) exam.