Editing 802.1q

= IEEE 802.1Q =

'''IEEE 802.1Q''' is a networking standard that defines '''Virtual LAN (VLAN) tagging''' on Ethernet networks. It allows multiple VLANs to be carried over a single physical link, a process known as '''VLAN trunking'''.

== Overview ==
802.1Q works by inserting a 4-byte tag into an Ethernet frame. This tag identifies the VLAN to which the frame belongs, enabling network switches to separate traffic logically while sharing the same physical infrastructure.

== Frame Format ==
The 802.1Q tag includes:
* '''Tag Protocol Identifier (TPID)''' – Identifies the frame as VLAN-tagged
* '''Priority Code Point (PCP)''' – Used for Quality of Service (QoS)
* '''Drop Eligible Indicator (DEI)''' – Indicates congestion eligibility
* '''VLAN ID (VID)''' – Identifies the VLAN (range 1–4094)

== Native VLAN ==
Frames belonging to the '''native VLAN''' are sent untagged on 802.1Q trunk links by default. This behavior can be configured and is often changed for security reasons.

== Uses ==
802.1Q is commonly used in enterprise and data center networks to:
* Segment broadcast domains
* Improve network security
* Support scalable network design

== References ==
* IEEE Standard 802.1Q