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Configuring Interfaces

Configuring Layer 3 Interfaces

The switch must be running the IP services image to support Layer 3 interfaces:

 SVIs: You should configure SVIs for any VLANs for which you want to route traffic. SVIs are created when you enter

a VLAN ID following the interface vlan global configuration command. To delete an SVI, use the no interface vlan

global configuration command. You cannot delete interface VLAN 1.

When you create an SVI, it does not become active until it is associated with a physical port.

 Routed ports: Routed ports are physical ports configured to be in Layer 3 mode by using the no switchport interface

configuration command.

 Layer 3 EtherChannel ports: EtherChannel interfaces made up of routed ports.

A Layer 3 switch can have an IP address assigned to each routed port and SVI.

There is no defined limit to the number of SVIs and routed ports that can be configured in a switch. However, the

interrelationship between the number of SVIs and routed ports and the number of other features being configured might

have an impact on CPU usage because of hardware limitations. If the switch is using maximum hardware resources,

attempts to create a routed port or SVI have these results:

 If you try to create a new routed port, the switch generates a message that there are not enough resources to convert

the interface to a routed port, and the interface remains as a switch port.

 If you try to create an extended-range VLAN, an error message is generated, and the extended-range VLAN is

rejected.

 If the switch attempts to boot up with a configuration that has more VLANs and routed ports than hardware can

support, the VLANs are created, but the routed ports are shut down, and the switch sends a message that this was

due to insufficient hardware resources.

All Layer 3 interfaces require an IP address to route traffic. This procedure shows how to configure an interface as a Layer

3 interface and how to assign an IP address to an interface.

Note: If the physical port is in Layer 2 mode (the default), you must enter the no switchport interface configuration

command to put the interface into Layer 3 mode. Entering a no switchport command disables and then re-enables the

interface, which might generate messages on the device to which the interface is connected. Furthermore, when you put

an interface that is in Layer 2 mode into Layer 3 mode, the previous configuration information related to the affected

interface might be lost, and the interface is returned to its default configuration

Beginning in privileged EXEC mode, follow these steps to configure a Layer 3 interface:

Command Purpose

1. configure terminal Enter global configuration mode.

2. interface {{fastethernet | gigabitethernet} interface-id} |

{vlan vlan-id} | {port-channel port-channel-number}

Specify the interface to be configured as a Layer 3

interface, and enter interface configuration mode.

3. no shutdown Enable the port, if necessary. By default, UNIs and ENIs

are disabled, and NNIs are enabled.

4. no switchport For physical ports only, enter Layer 3 mode.

5. ip address ip_address subnet_mask Configure the IP address and IP subnet.

6. no shutdown Enable the interface.

Cisco IE-5000 User Manual

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