LAN

LAN - A group of devices in the same broadcast domain

Broadcast domain - A logical area in a network where broadcast MAC address (FF:FF:FF:FF:FF:FF) frames are forwarded to all devices within that segment

• Essentially, a network area where any device can send a message that every other device in that area will receive

When we connect a group of devices to a [[1.2 - Networking Devices#Switch|switch]], they are in the same broadcast domain

VLAN

VLAN - A group of devices in the same broadcast domain, but separated logically instead of physically

• e.g. a single switch can have two different virtual LANs that devices can be a part of

VLANs are defined by number and configured in the switch (VLAN database).

VLANS can be connected across different switches.

• This can be done by connecting the VLANs via ethernet cable, but this is not scalable.
• Instead, this can be achieved by using a VLAN Trunk

Trunking

VLAN Trunk (802.1Q Trunk, .1Q Trunk) - A single ethernet connection between switches configured as a "Trunk Interface"

Anything sent from VLAN 1 on one switch will arrive at VLAN 1 on another switch via this connection.

How it Works A VLAN header containing a 12-bit VLAN ID is added to the ethernet frame, allowing for 4,094 VLANs to traverse the trunk connection.

Before 802.1Q, there was ISL (Inter-Switch Link)

• No longer used

Default VLAN The VLAN that new devices are connected to by default

• Most commonly VLAN 1

Native VLAN - connects switches without a tag Every trunk has a native VLAN that doesn't use an 802.1Q header

• Used to communicate with devices that don't use 802.1Q
• Native VLAN should match between switches

Layer 3 Switches

A switch and router in a single device

• Switching still operates at layer 2
• Routing still operates at layer 3

Allows for routing between VLANs on the same switch

Internal router connects to the VLANs over VLAN interfaces (also called switched virtual interfaces (SVI))

Voice and Data

Voice and data contend with each other. To mitigate this, put computers on one VLAN and phones on another.

One wire connecting the computer and phone to one switch interface.

Voice and data is split up because each switch interface has a voice VLAN and data VLAN.