Users Guide

Native VLAN is useful in deployments where a Layer 2 port can receive both tagged and untagged traffic on
the same physical port. The classic example is connecting a voice-over-IP (VOIP) phone and a PC to the
same port of the switch. The VOIP phone is configured to generate tagged packets (with VLAN = VOICE
VLAN) and the attached PC generates untagged packets.
NOTE: When a hybrid port is untagged in a VLAN but it receives tagged traffic, all traffic is accepted.
NOTE: You cannot configure an existing switchport or port channel interface for Native VLAN. Interfaces
must have no other Layer 2 or Layer 3 configurations when using the portmode hybrid command or a
message similar to this displays: % Error: Port is in Layer-2 mode Gi 5/6.
To configure a port so that it can be a member of an untagged and tagged VLANs, use the following
commands.
1 Remove any Layer 2 or Layer 3 configurations from the interface.
INTERFACE mode
2 Configure the interface for Hybrid mode.
INTERFACE mode
portmode hybrid
3 Configure the interface for Switchport mode.
INTERFACE mode
switchport
4 Add the interface to a tagged or untagged VLAN.
VLAN INTERFACE mode
[tagged | untagged]
Enabling Null VLAN as the Default VLAN
In a Carrier Ethernet for Metro Service environment, service providers who perform frequent reconfigurations
for customers with changing requirements occasionally enable multiple interfaces, each connected to a
different customer, before the interfaces are fully configured.
This presents a vulnerability because both interfaces are initially placed in the native VLAN, VLAN 1, and for
that period customers are able to access each other's networks. Dell Networking OS has a Null VLAN to
eliminate this vulnerability. When you enable the Null VLAN, all ports are placed into it by default, so even if
you activate the physical ports of multiple customers, no traffic is allowed to traverse the links until each port
is place in another VLAN.
To enable Null VLAN, use the following command.
• Disable the default VLAN, so that all ports belong to the Null VLAN until configured as a member of
another VLAN.
CONFIGURATION mode
default-vlan disable
Default: the default VLAN is enabled (no default-vlan disable).
Virtual LANs (VLANs) 1019