2.2 Given a scenario, configure switching technologies and features

VLAN

📘CompTIA Network+ (N10-009)

What Is a VLAN Database?

A VLAN database is the location on a switch where VLAN configuration information is stored.
It keeps track of:

VLAN IDs
VLAN names
VLAN status (active / suspended)
VLAN assignment information

The VLAN database allows switches to keep VLAN configuration even after a reboot.

Why the VLAN Database Matters

For the exam, you must understand:

Where VLAN information is stored
How switches save VLAN data
How VLAN data is shared or synchronized
Differences between VLAN storage types depending on the switch platform
How to add, remove, and verify VLANs

How VLAN Information Is Stored

Modern networks use two main storage methods:

✅ 1. VLAN Database Stored in NVRAM (vlan.dat file)

Cisco-style switches store VLAN information in a file called vlan.dat.

Location: Flash memory / NVRAM
Contains:
- VLAN IDs
- VLAN names
- Voice VLANs
- Custom VLANs
Stays saved after reboot

Key Point for the Exam:

Even if you erase the startup-config, your VLANs still exist because they are saved in vlan.dat, not inside the main configuration file.

✅ 2. VLAN Database Stored in Running-Config / Startup-Config

Some switch platforms (especially newer or non-Cisco brands) store VLANs directly in the running configuration:

VLANs saved in running-config
Copied to startup-config using the normal save process
No separate vlan.dat file

Exam Tip:

Network+ does not focus on brand-specific differences — but you should know that switches may store VLANs in different locations depending on OS.

How VLANs Are Added to the Database

When you create a VLAN on a switch, it is immediately added to the VLAN database.

Example (concept level, not Cisco-specific):

vlan 10
  name Engineering

This creates:

VLAN ID: 10
VLAN Name: Engineering

The switch writes this info into:

vlan.dat (on Cisco-style switches)
OR the running config (on other software types)

How VLANs Are Removed from the Database

Removing a VLAN deletes it from the VLAN database.

Important:

Any ports assigned to that VLAN become inactive until moved to a valid VLAN.
If the VLAN is part of trunk allowed lists, it is removed from trunking capability.

How VLAN Information Is Shared Between Switches

VLAN information is not automatically shared between switches unless a VLAN management protocol is used, such as:

Legacy: VTP (VLAN Trunking Protocol)

Can propagate VLAN database changes to other switches
Not commonly used today outside of old Cisco networks
Network+ may mention it conceptually, but not in depth

Modern approach: Manually configure VLANs on each switch

Most admins manually create needed VLANs on each switch
Trunks simply carry the VLAN tags

Exam Tip:
VLANs do not magically appear on another switch unless you configure them there.

VLAN Database and Trunk Links

A trunk link can only pass a VLAN if:

The VLAN exists in the switch’s VLAN database
The VLAN is allowed on the trunk port

If the VLAN does not exist in the database:

The switch will drop frames for that VLAN
The interface will mark traffic as “unknown VLAN”

VLAN Database and Access Ports

If you assign an access port to a VLAN:

The VLAN must exist in the database
If it doesn’t exist, the switch will reject the configuration or keep it inactive

Example:

Assigning port to VLAN 30 requires VLAN 30 to exist in database.

VLAN Range Types Stored in VLAN Database

Network+ wants you to know the common VLAN range classifications:

Standard VLANs (1–1005)

Normal operational VLANs
Typically stored in vlan.dat
Supported everywhere

Extended VLANs (1006–4094)

Used in larger networks
Require 802.1Q
Often stored in running-config (depending on switch platform)

Reserved VLANs

VLAN 0 and 4095 – protocol operations
VLAN 1 – default VLAN
Cannot be removed from database

How to Verify VLAN Database

Switches show VLAN database contents with commands such as:

show vlan
show vlan brief
show vlan id 10

Information displayed:

VLAN ID
VLAN name
Ports assigned
Status (active/suspended)

Exam-Focused Points to Remember

You MUST know these for Network+:

✔ VLANs are stored in a VLAN database

✔ Database may be vlan.dat OR the switch config

✔ VLANs stay after reboot

✔ Trunks only pass VLANs that exist in database

✔ Removing a VLAN deletes all port membership

✔ VLAN ranges (standard, extended, reserved)

✔ VLANs are not automatically shared across switches

✔ Must manually create VLANs unless a protocol like VTP is used

Short Summary for Website Posting

VLAN database = storage location for VLAN information
Keeps VLAN IDs, names, and status persistent
Stored in vlan.dat or in configuration file
Required for access ports and trunk ports
VLAN must exist in the database before being used
Removal affects all assigned ports
Critical for managing segmented networks