What is a VLAN ID?
A VLAN ID is an identifier used to distinguish individual VLANs (virtual L2 segments) in a network utilizing VLAN technology. VLAN (Virtual LAN) refers to a technology that allows a single physical L2 switch to be divided into multiple virtual L2 switches (L2 segments). Additionally, multiple physical switches can be combined into one logical switch, which can then be divided into multiple virtual L2 segments.
There are two primary reasons to divide a network into multiple L2 segments:
Limiting the Broadcast Domain:
A broadcast domain defines the extent to which broadcast frames can propagate, which corresponds to an L2 segment. If a broadcast domain becomes too large, the number of broadcast frames processed by each host increases, unnecessarily consuming CPU and other resources.
Enhancing Security:
By separating hosts with different security levels into separate L2 segments, direct communication between them is prevented, requiring routes to pass through a router. Enforcing proper security settings on the router further improves communication security.
VLAN technology, introduced in the 1990s, remains widely used in data centers and corporate internal networks. However, VLAN IDs are defined with 12 bits, limiting the maximum number of L2 segments to approximately 4,000, which can be insufficient for large-scale networks. To address this limitation, technologies like VXLAN (Virtual eXtensible Local Area Network) and NVGRE (Network Virtualization using Generic Routing Encapsulation) have emerged. These technologies feature 24-bit IDs, enabling the creation of approximately 16 million L2 segments. They can also overlay existing VLAN-configured networks, simplifying transitions from traditional setups to these advanced solutions.