VLAN tags are used in Ethernet frames to identify and differentiate traffic between multiple VLANs. They are especially important for devices like switches that handle multiple VLANs on the same physical link.
Step-by-Step Breakdown:
VLAN Tag Contents:
VLAN ID: The tag contains a 12-bit VLAN ID field that identifies the VLAN to which the frame belongs.
Priority: The tag also includes a 3-bit priority field (also known as 802.1p priority) used for QoS (Quality of Service) to prioritize traffic.
Trunk Ports and VLAN Tagging:
Trunk Ports are used to carry traffic for multiple VLANs across a single link. These interfaces insert (tag) VLAN identifiers into frames when they leave the switch and remove (untag) them when frames enter the switch.
Access Ports:
VLAN tags are typically not used on access ports (ports that connect to end devices) since those ports are configured to be part of a single VLAN, and the traffic doesn't need VLAN tags.
Juniper Reference:
VLAN Tagging: Juniper switches support VLAN tagging and ensure that frames are tagged or untagged as they traverse trunk or access ports, respectively.