Reference Guide

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).
772 Virtual LANs (VLANs)