VLAN

A VLAN is a logical grouping of network endpoints connected to defined ports on a switch, allowing the segmentation of networks by creating logical broadcast domains that can span multiple physical LAN segments.

With VLANs, network administrators can segment networks based on factors such as team, function, department, or application, without worrying about the physical location of endpoints and users.
A broadcast packet sent over one VLAN does not reach any other endpoint that is a member of another VLAN.
Because each VLAN is regarded as a broadcast domain, it needs to have its own subnet; for example, the network administrator contracted by XQ can segment the network by departments:

Department	VLAN ID	Subnet
`Servers`	`VLAN 10`	`192.168.1.0/24`
`C-Level`	`VLAN 20`	`192.168.2.0/24`
`Finance`	`VLAN 30`	`192.168.3.0/24`
`HR`	`VLAN 40`	`192.168.4.0/24`
`Marketing`	`VLAN 50`	`192.168.5.0/24`
`Support`	`VLAN 60`	`192.168.6.0/24`

VLAN Identification

Standard 802.3 Ethernet frames do not contain VLAN information; therefore, switches and other VLAN-enabled devices need a mechanism to keep track of all the VLAN information associated with a packet while traversing VLAN-enabled devices. Two main trunking methods are utilized to achieve this, ISL and IEEE 802.1Q.

IEEE 802.1Q

To ensure interoperability of VLAN technologies from the various network-equipments vendors, the Institute of Electrical and Electronics Engineers (IEEE) developed the 802.1Q specification in 1998.

The IEEE 802 committee had to change the IEEE 802.3 Ethernet frame format by adding a pair of 2-byte fields, TPID and TCI (which consists of three subfields, PCP, DEI, and VID), resulting in a VLAN-compliant 802.1Q Ethernet frame.

Diagram showing conversion of a 802.3 Ethernet frame to a 802.1Q Ethernet frame by inserting a 802.1Q header between the source address and length fields. The 802.1Q header includes TPID, PCP, DEI, and VID.

Assigning NICs a VLAN in Linux

sudo modprobe 8021q

lsmod | grep 8021

sudo vconfig add eth0 20