Administrator Guide

protocol lldp
no shutdown
Preserving 802.1Q VLAN Tag Value for Lite
Subinterfaces
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.
Flex Hash and Optimized Boot-Up
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