Dell Configuration Guide for the S4048–ON System 9.14.2.6

All the frames in a Layer 2 VLAN are identified using a tag defined in the IEEE 802.1Q standard to determine the VLAN to which the frames or traffic are relevant or associated. Such frames are encapsulated with the 802.1Q tags. If a single VLAN is configured in a network topology, all the traffic packets contain the same do1q tag, which is the tag value of the 802.1Q header. If a VLAN is split into multiple, different sub-VLANs, each VLAN is denoted by a unique 8021.Q tag to enable the nodes that receive the traffic frames determine the VLAN for which the frames are destined.

Typically, a Layer 3 physical interface processes only untagged or priority-tagged packets. Tagged packets that are received on Layer 3 physical interfaces are dropped. To enable the routing of tagged packets, the port that receives such tagged packets needs to be configured as a switchport and must be bound to a VLAN as a tagged member port.

A lite subinterface is similar to a normal Layer 3 physical interface, except that additional provisioning is performed to set the VLAN ID for encapsulation.

A physical interface or a Layer 3 Port channel interface can be configured as a lite subinterface. Once a lite subinterface is configured, only tagged IP packets with encapsulation VLAN ID are processed and routed. All other data packets are discarded except the Layer 2 and Layer 3 control frames. It is not required for a VLAN ID to be preserved (in the hardware or the OS application) when a VLAN ID, used for encapsulation, is associated with a physical/Port-channel interface. Normal VLANs and VLAN encapsulation can exist simultaneously and any non-unicast traffic received on a normal VLAN is not flooded using lite subinterfaces whose encapsulation VLAN ID matches with that of the normal VLAN ID.

You can use the encapsulation dot1q vlan-id command in INTERFACE mode to configure lite subinterfaces.