VLANIDs

VLAN IDs are numerical labels used to identify VLANs in IEEE 802.1Q networks. The VLAN ID (VID) is carried in the 802.1Q tag and determines which VLAN a frame belongs to as it passes through switches. VLANs partition broadcast domains, enabling traffic separation, security policies, and scalable network design. On a switch, access ports are assigned to a single VLAN, while trunk links carry traffic for multiple VLANs, with each frame tagged by its VID. Inter-VLAN routing is performed by a Layer 3 device to enable communication between VLANs.

The valid range for VLAN IDs is 0 to 4095. In practice, 0 is reserved for priority-tagged frames that carry only Quality of Service information without a specific VLAN, and 4095 is reserved for special use in some contexts. Therefore, usable VLAN IDs are typically 1 through 4094. Administrators assign VLAN IDs to reflect organizational groups, functions, or security domains (for example, VLAN 10 for Finance, VLAN 20 for Engineering). The VLAN ID is a label; it does not by itself define IP addressing. Each VLAN can be associated with one or more IP subnets, and routing between VLANs is handled by a router or Layer 3 switch.

Best practices include avoiding reliance on VLAN 1 as a security boundary, documenting VLAN-to-subnet mappings, and ensuring consistent tagging on trunk links. VLAN IDs support scalable network design but require complementary security and access policies to enforce segmentation.