Reference Guide

NOTE: You cannot assign an IP address to the Default VLAN. To assign an IP address to a VLAN that is currently
the Default VLAN, create another VLAN and assign it to be the Default VLAN. For more information about assigning
IP addresses, refer to Assigning an IP Address to a VLAN.
• Untagged interfaces must be part of a VLAN. To remove an untagged interface from the Default VLAN, create
another VLAN and place the interface into that VLAN. Alternatively, use the no switchport command, and
FTOS removes the interface from the Default VLAN.
• 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
FTOS(conf)#int gi 3/2
FTOS(conf-if)#no shut
FTOS(conf-if)#switchport
FTOS(conf-if)#show config
!
interface GigabitEthernet 3/2
no ip address
switchport
no shutdown
FTOS(conf-if)#end
FTOS#
show vlan
Codes: * - Default VLAN, G - GVRP VLANs
NUM Status Q Ports
* 1 Active U Gi 3/2
2 Active T Po1(So 0/0-1)
T Gi 3/0
FTOS#
Port-Based VLANs
Port-based VLANs are a broadcast domain defined by different ports or interfaces. In FTOS, a port-based VLAN can
contain interfaces from different line cards within the chassis. FTOS 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.
FTOS 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.
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