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. The system 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).
920 Virtual LANs (VLANs)