VLANs and Port TaggingTo add an interface to a VLAN, the interface must be in Layer 2 mode. After you place an interface in Layer 2 mode, the interface isautomatically placed in the Default VLAN.Dell Networking OS supports IEEE 802.1Q tagging at the interface level to filter traffic. When you enable tagging, a tag header is added tothe frame after the destination and source MAC addresses. That information is preserved as the frame moves through the network. Thefollowing example shows the structure of a frame with a tag header. The VLAN ID is inserted in the tag header.Figure 128. Tagged Frame FormatThe tag header contains some key information that Dell Networking OS uses:• The VLAN protocol identifier identifies the frame as tagged according to the IEEE 802.1Q specifications (2 bytes).• Tag control information (TCI) includes the VLAN ID (2 bytes total). The VLAN ID can have 4,096 values, but two are reserved.NOTE: The insertion of the tag header into the Ethernet frame increases the size of the frame to more than the 1,518 bytes asspecified in the IEEE 802.3 standard. Some devices that are not compliant with IEEE 802.3 may not support the larger framesize.Information contained in the tag header allows the system to prioritize traffic and to forward information to ports associated with a specificVLAN ID. Tagged interfaces can belong to multiple VLANs, while untagged interfaces can belong only to one VLAN.Configuration Task ListThis section contains the following VLAN configuration tasks.• Creating a Port-Based VLAN (mandatory)• Assigning Interfaces to a VLAN (optional)• Assigning an IP Address to a VLAN (optional)• Enabling Null VLAN as the Default VLANCreating a Port-Based VLANTo configure a port-based VLAN, create the VLAN and then add physical interfaces or port channel (LAG) interfaces to the VLAN.NOTE: The Default VLAN (VLAN 1) is part of the system startup configuration and does not requireconfiguration.A VLAN is active only if the VLAN contains interfaces and those interfaces are operationally up. As shown in the following example, VLAN 1is inactive because it does not contain any interfaces. The other VLANs contain enabled interfaces and are active.NOTE: In a VLAN, the shutdown command stops Layer 3 (routed) traffic only. Layer 2 traffic continues to pass through theVLAN. If the VLAN is not a routed VLAN (that is, configured with an IP address), the shutdown command has no affect onVLAN traffic.When you delete a VLAN (using the no interface vlan vlan-id command), any interfaces assigned to that VLAN are assigned tothe Default VLAN as untagged interfaces.To create a port-based VLAN, use the following command.Virtual LANs (VLANs) 861
