Interfaces | 477
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).
The example below shows how the
show config command displays an example of a Layer 3 interface.
FTOS(conf-if)#show config
!
interface GigabitEthernet 1/5
ip address 10.10.10.1 /24
no shutdown
FTOS(conf-if)#
If an interface is in the incorrect layer mode for a given command, an error message is displayed to the
user. In the example below, 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.
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, 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.
ip address ip-address mask [secondary] INTERFACE Configure a primary IP address and mask on
the interface. The ip-address must be in
dotted-decimal format (A.B.C.D) and the
mask must be in slash format (/xx).
Add the keyword secondary if the IP address
is the interface’s backup IP address.
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