Reference Guide

Interfaces | 375
For information on enabling and configuring Spanning Tree Protocol, see Chapter 10, Layer 2, on page 47.
To view the interfaces in Layer 2 mode, use the command
show interfaces switchport in the EXEC mode.
Configure Layer 3 (Network) Mode
When you assign an IP address to a physical interface, you place it in Layer 3 mode. Use the ip address
command and
no shutdown command in INTERFACE mode to enable Layer 3 mode on an individual
interface. 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).
Figure 19-5 shows how the
show config command displays an example of a Layer 3 interface.
Figure 19-5. show config Command Example of a Layer 3 Interface
If an interface is in the incorrect layer mode for a given command, an error message is displayed to the
user. For example, in Figure 19-6, the command
ip address triggered an error message because the
interface is in Layer 2 mode and the
ip address command is a Layer 3 command only.
Figure 19-6. Error Message When Trying to Add an IP Address to Layer 2 Interface
To determine the configuration of an interface, you can use the show config command in INTERFACE
mode or the various
show interface commands in EXEC mode.
To assign an IP address, use both of the following commands in the INTERFACE mode:
Command Syntax Command Mode Purpose
no shutdown
INTERFACE Enable the interface.
FTOS(conf-if)#show config
!
interface GigabitEthernet 1/5
ip address 10.10.10.1 /24
no shutdown
FTOS(conf-if)#
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)#
Error message