MISSION CONTROL
TRAINING DUEL RANKS

LOGBOOK

  • No tags found
Scanning...
  • Type at least 2 characters to search...

HELP

1 / 20
Other keys: show • Space: good • 1-4: rate • 0: skip • 5: flag

Question

What is a VLAN and what are its key benefits?

Answer

A VLAN (Virtual Local Area Network) is a logical grouping of devices on one or more switches that creates separate broadcast domains, regardless of physical location.

Physical switches split into separate logical VLAN broadcast domains regardless of location.

VLANs as logical broadcast domains across switches. — Michel Bakni, CC BY-SA 4.0, via Wikimedia Commons.

Without VLANs, all devices connected to a switch share the same broadcast domain — every broadcast reaches every device. VLANs solve this by creating logical segments at Layer 2.

Key benefits:

Benefit Why It Matters
Smaller broadcast domains Fewer devices receive each broadcast → less wasted bandwidth
Improved security Only devices in the same VLAN can communicate directly at Layer 2
Improved IT efficiency Group devices by function (e.g., faculty vs. students) rather than physical location
Reduced cost One switch can serve multiple groups — no need for separate physical switches
Better performance Smaller domains = less unnecessary traffic
Simpler management Similar groups share the same applications and network policies

Each VLAN gets its own IP (Internet Protocol) subnet (e.g., VLAN 10 = 10.0.2.0/24, VLAN 20 = 10.0.3.0/24). Devices in different VLANs cannot communicate without a Layer 3 device (router or Layer 3 switch).

Tip: Think of VLANs as invisible walls inside a switch — devices on the same VLAN can talk freely, but crossing VLAN boundaries requires a router.

Go deeper:

  • chart Virtual LAN (Wikipedia) — defines VLANs as logical broadcast domains and lays out the segmentation/security/management benefits, with topology diagrams.
The general concept of virtual LANs.
The general concept of virtual LANs.
Michel Bakni · CC BY-SA 4.0 · Wikimedia Commons
or press any other key

Question

What is VLAN 1, and why does Cisco recommend moving its default functions to other VLANs?

Answer

VLAN (Virtual Local Area Network) 1 is the default VLAN on Cisco switches — it serves as the default data VLAN, native VLAN, and management VLAN, and it cannot be deleted or renamed.

VLAN 1's three default roles:

  1. Default VLAN — all switch ports are members of VLAN 1 out of the box
  2. Default Native VLAN — untagged traffic on trunk links is assumed to belong to VLAN 1
  3. Default Management VLAN — SSH/Telnet management traffic uses VLAN 1

Why move away from VLAN 1?

Security. Since VLAN 1 is the well-known default, attackers know to target it. Cisco best practice is to:

  • Assign user data traffic to other VLANs (e.g., VLAN 10, 20, 30)
  • Change the native VLAN on trunks to something other than VLAN 1 (e.g., VLAN 99)
  • Use a dedicated management VLAN for switch administration

You can also see the legacy VLANs (1002–1005) in show vlan brief — these exist for FDDI and Token Ring compatibility and also cannot be deleted.

Go deeper:

or press any other key