Reference Guide

– secondary — This is the interface’s backup IP address. You can configure up to eight secondary IP
addresses.
Configuring Native VLANs
Traditionally, ports can be either untagged for membership to one VLAN or tagged for membership to multiple VLANs.
You must connect an untagged port to a VLAN-unaware station (one that does not understand VLAN tags), and you must
connect a tagged port to a VLAN-aware station (one that generates and understands VLAN tags).
Native VLAN support breaks this barrier so that you can connect a port to both VLAN-aware and VLAN-unaware
stations. Such ports are referred to as hybrid ports. Physical and port-channel interfaces may be hybrid ports.
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. FTOS 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
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