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Configuring Layer 3 Interfaces
Configuring Layer 3 Interfaces
The Cisco 3400 ME switch must be running the metro IP access image to support Layer 3 interfaces.
The Cisco ME switch supports these types of Layer 3 interfaces:
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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:
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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.
If the physical port is in Layer 2 mode (the default), you must enter the no switchport interface
Note
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
Step 1
configure terminal
Step 2
interface {{fastethernet | gigabitethernet} interface-id}
| {vlan vlan-id} | {port-channel port-channel-number}
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
9-20
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.
Note
When you create an SVI, it does not become active until it is associated with a physical port.
For information about assigning Layer 2 ports to VLANs, see
VLANs."
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.
EtherChannel port interfaces are described in
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.
Chapter 9
Configuring Interface Characteristics
Chapter 31, "Configuring EtherChannels."
Purpose
Enter global configuration mode.
Specify the interface to be configured as a Layer 3
interface, and enter interface configuration mode.
Chapter 11, "Configuring
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