Reference Guide

Configuring Layer 2 (Interface) Mode
To configure an interface in Layer 2 mode, use the following commands.
• Enable the interface.
INTERFACE mode
no shutdown
• Place the interface in Layer 2 (switching) mode.
INTERFACE mode
switchport
For information about enabling and configuring the Spanning Tree Protocol, refer to Spanning Tree Protocol (STP).
To view the interfaces in Layer 2 mode, use the show interfaces switchport command in EXEC mode.
Configuring Layer 3 (Network) Mode
When you assign an IP address to a physical interface, you place it in Layer 3 mode.
To enable Layer 3 mode on an individual interface, use the following commands. In all interface types except VLANs, the
shutdown command prevents all traffic from passing through the interface. In VLANs, the shutdown command
prevents Layer 3 traffic from passing through the interface. Layer 2 traffic is unaffected by the shutdown command.
One of the interfaces in the system must be in Layer 3 mode before you configure or enter a Layer 3 protocol mode (for
example, OSPF).
• Enable Layer 3 on an individual interface
INTERFACE mode
ip address
• Enable the interface.
INTERFACE mode
no shutdown
If an interface is in the incorrect layer mode for a given command, an error message is displayed (shown in bold). In the
following example, the ip address command triggered an error message because the interface is in Layer 2 mode
and the
ip address command is a Layer 3 command only.
Example of Error Due to Issuing a Layer 3 Command on a Layer 2 Interface
FTOS(conf-if)#show config
!
interface GigabitEthernet 1/2
no ip address
switchport
no shutdown
FTOS(conf-if)#ip address 10.10.1.1 /24
% Error: Port is in Layer 2 mode Gi 1/2.
FTOS(conf-if)#
To determine the configuration of an interface, use the show config command in INTERFACE mode or the various
show interface commands in EXEC mode.
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