Administrator Guide

• A tagged interface requires an additional step to remove it from Layer 2 mode. Because tagged interfaces can belong to multiple
VLANs, remove the tagged interface from all VLANs using the no tagged interface command. Only after the interface is
untagged and a member of the Default VLAN can you use the no switchport command to remove the interface from Layer 2
mode. For more information, refer to VLANs and Port Tagging.
Example of Configuring an Interface for Layer 2 Belonging to the Default VLAN
Dell(conf)#int te 2/2
Dell(conf-if)#no shut
Dell(conf-if)#switchport
Dell(conf-if)#show config
!
interface TenGigabitEthernet 2/2
no ip address
switchport
no shutdown
Dell(conf-if)#end
Dell#show vlan
Codes: * - Default VLAN, G - GVRP VLANs
NUM Status Q Ports
* 1 Active U Te 2/2
2 Active T Po1(Te 0/0-1)
T Te 2/0
Dell#
Port-Based VLANs
Port-based VLANs are a broadcast domain defined by different ports or interfaces. A port-based VLAN can contain interfaces from
different line cards within the chassis. The system supports 4094 port-based VLANs.
Port-based VLANs offer increased security for traffic, conserve bandwidth, and allow switch segmentation. Interfaces in different VLANs
do not communicate with each other, adding some security to the traffic on those interfaces. Different VLANs can communicate between
each other by means of IP routing. Because traffic is only broadcast or flooded to the interfaces within a VLAN, the VLAN conserves
bandwidth. Finally, you can have multiple VLANs configured on one switch, thus segmenting the device.
Interfaces within a port-based VLAN must be in Layer 2 mode and can be tagged or untagged in the VLAN ID.
VLANs and Port Tagging
To 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 is
automatically placed in the Default VLAN.
The system supports IEEE 802.1Q tagging at the interface level to filter traffic. When you enable tagging, a tag header is added to the
frame after the destination and source MAC addresses. That information is preserved as the frame moves through the network. The
following example shows the structure of a frame with a tag header. The VLAN ID is inserted in the tag header.
Figure 147. Tagged Frame Format
The tag header contains some key information that the system 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 as specified in the IEEE 802.3 standard. Some devices that are not compliant with IEEE 802.3 may not support the
larger frame size.
Information contained in the tag header allows the system to prioritize traffic and to forward information to ports associated with a
specific VLAN ID. Tagged interfaces can belong to multiple VLANs, while untagged interfaces can belong only to one VLAN.
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Virtual LANs (VLANs)