Reference Guide

Virtual LANs (VLAN) | 941
Untagged interfaces must be part of a VLAN. To remove an untagged interface from the Default VLAN,
you must create another VLAN and place the interface into that VLAN. Alternatively, enter the
no
switchport
command, and Dell networking OS removes the interface from the Default VLAN.
A tagged interface requires an additional step to remove it from Layer 2 mode. Since tagged interfaces can
belong to multiple VLANs, you must 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, see VLANs
and Port Tagging.
Port-Based VLANs
Port-based VLANs are a broadcast domain defined by different ports or interfaces. Dell networking OS
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, it must be in Layer 2 mode. After you place an interface in Layer 2 mode,
it is automatically placed in the Default VLAN. Dell networking OS supports IEEE 802.1Q tagging at the
interface level to filter traffic. When tagging is enabled, 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. Figure 54-2 illustrates the structure of a frame with a tag header. The VLAN ID is inserted in the
tag header.
Figure 54-2. Tagged Frame Format
The tag header contains some key information used by Dell networking OS:
• The VLAN protocol identifier identifies the frame as tagged according to the IEEE 802.1Q
specifications (2 bytes).
Et h er n et
Preamble Destination
Address
So ur c e
Address
Ta g
Header
Protocol
Ty p e
Data
45 - 1500 octets2 octets4 octets 4 octets6 octets 6 octets
Fr am e
Check
Se q u e n c e