What is the difference of TAG and UNTAGGED in VLAN Switch Configuration?

In VLAN (Virtual Local Area Network) switch configuration, "tagged" and "untagged" are terms used to describe how VLAN traffic is handled on switch ports. Here are the key differences:

Untagged

Definition: An untagged port is a port that belongs to a single VLAN and does not include a VLAN tag in the Ethernet frames.

Use Case: Used to connect end devices (like PCs, printers, etc.) that do not understand VLAN tagging.

Behavior: Frames sent from an untagged port are not marked with a VLAN tag. When a frame is received on an untagged port, it is assumed to belong to the VLAN assigned to that port.

Example: If port 1 is untagged in VLAN 10, any device connected to port 1 sends and receives traffic as if it is on VLAN 10, but without any VLAN tags in the Ethernet frames.

Tagged

Definition: A tagged port is a port that can carry traffic for multiple VLANs, and it includes VLAN tags in the Ethernet frames to indicate which VLAN the traffic belongs to.

Use Case: Used for connections between switches (trunk links) or between a switch and a device that understands VLAN tags (like a server or a router).

Behavior: Frames sent from a tagged port include a VLAN tag in the Ethernet frame header. When a frame is received on a tagged port, the switch uses the VLAN tag to determine which VLAN the frame belongs to.

Example: If port 2 is tagged for VLANs 10 and 20, it can carry traffic for both VLANs. Frames will have VLAN tags indicating whether they belong to VLAN 10 or VLAN 20.

Practical Example:

Untagged Port (Access Port):

Port 1 is configured as an untagged member of VLAN 10.

Device A connected to Port 1 communicates without VLAN tags.

>All traffic to/from Device A is associated with VLAN 10.

Tagged Port (Trunk Port):

Port 2 is configured as a tagged member of VLANs 10 and 20.

This port can be connected to another switch or a router that understands VLAN tags.

Traffic on Port 2 will include VLAN tags to distinguish between VLAN 10 and VLAN 20.

Key Points:

Untagged Ports: Simpler, for single VLAN, no VLAN tags.

Tagged Ports: More flexible, for multiple VLANs, includes VLAN tags.

By understanding these concepts, network administrators can design and configure their VLAN setups to ensure proper traffic segregation and management.