zaro

What is VLAN ID?

Published in Network Concepts 3 mins read

A VLAN ID (VID) is a unique identifier that specifies which Virtual Local Area Network (VLAN) a data frame belongs to. This identifier allows network devices, like switches, to understand how to correctly transmit frames within the defined VLAN.

Understanding VLAN IDs

VLANs are used to segment a network into smaller, more manageable broadcast domains. This segmentation improves network performance, security, and manageability. The VLAN ID is a critical component in this process. Here's how it works:

  • VLAN Tagging: When a device sends a data frame within a VLAN, the frame is tagged with a VLAN ID. This tag is typically inserted into the Ethernet header and informs network devices about the VLAN membership of the frame.

  • Frame Identification: Network devices, particularly switches, read the VLAN ID in the frame's tag. This allows the switch to forward the frame only to ports that are members of the same VLAN. This avoids sending frames to unrelated parts of the network.

  • Reference Information: According to the provided information, the VLAN ID (VID) field in a data frame identifies the VLAN to which the data frame belongs (the VLAN in which the data frame can be transmitted). All frames processed on a switch carry VLAN tags.

How VLAN IDs Work in Practice

Here's a breakdown of the practical use of VLAN IDs:

  1. Tagging: When a device sends data on a VLAN, the network switch adds a VLAN tag containing the VID to the frame.
  2. Forwarding: Switches use the VLAN ID to direct the data frame only to ports configured to be part of the same VLAN, isolating traffic between different VLANs.
  3. Untagging: The switch removes the VLAN tag from frames before sending them to devices that cannot process tagged frames.

Example Scenarios

Let's consider some examples:

  • Scenario 1: You have a network with two departments: Sales and Engineering. You can assign VLAN 10 to the Sales department and VLAN 20 to Engineering. When a device in the Sales department sends a frame, it will be tagged with VID 10, which ensures it’s only forwarded to devices in VLAN 10.
  • Scenario 2: A single switch port may support multiple VLANs through the use of trunking, where frames belonging to different VLANs are forwarded over a single link. The VLAN ID is crucial in this situation to ensure the correct forwarding of frames to respective destinations.
  • Scenario 3: Some devices connected to a switch cannot process tagged frames. These devices need an untagged frame to be received. The switch will remove the tag before forwarding the frame to that device.

Key Takeaways

Here are the key things to remember about VLAN IDs:

  • Uniqueness: Each VLAN on the network must have a unique VLAN ID.
  • Standard: VLAN IDs are standardized in the IEEE 802.1Q standard.
  • Range: Usually, VLAN IDs range from 1 to 4094.
Concept Explanation
VLAN ID A unique identifier used to distinguish different VLANs.
VLAN Tag A field added to a data frame that includes the VLAN ID and other information, as per the IEEE 802.1Q standard.
Purpose To segment networks and control how data is transmitted within a VLAN domain.
Function Enables switches to identify which VLAN a data frame belongs to and to forward the frame only within that specific VLAN.

In summary, VLAN IDs are fundamental to how VLANs operate, allowing networks to efficiently and securely segregate traffic.