Layer 3 Ethernet Interfaces - Cisco Catalyst 2000 Configuration Handbook

72 Cisco LAN Switching Configuration Handbook
To provide connectivity between the different networks, the switch must have knowl-
■
edge of available pathways for these networks.

5-2: Layer 3 Ethernet Interfaces

■ Layer 3 switching requires an interface on the switch that can forward packets based
on Layer 3 addressing.
Each Layer 3 interface defines a separate broadcast domain and, therefore, a separate
■
network.
■ After a Layer 3 interface has been configured with a protocol, it can act as a gateway
for other devices in the same broadcast domain.
On some switches, you can configure an Ethernet port (interface) as a Layer 3 inter-
■
face.
Configuration
A Layer 3 interface is a direct routed interface that is designed to provide Layer 3 pro-
cessing of packets entering and exiting the interface. Not every physical interface on
every switch is designed to be a Layer 3 interface; however, on some switches, each port
is, or can be, configured to be a direct routed port. To configure these interfaces for
Layer 3 processing, use the following steps.
Select the physical Layer 3 interface:
1.
(global) interface type mod/port
Access global configuration mode and use this command to specify the interface and
move to interface configuration mode in the device. You must specify the type of
interfaces: ethernet, fastethernet, gigabitethernet, or tengigabitethernet. The
mod/port specifies the module and port number of the interface. Fixed-configura-
tion switches, such as the 2960, have no module option, and for switches like these,
the module (or slot) is always 0. However, when leveraging the Cisco StackWise
technology in 3750 and 3750-E series switches, there is a member switch number
that distinguishes a switch number for interface numbering switch/port.
Configure the interface for Layer 3 operation:
2.
(interface)no switchport
For multilayer switches, such as the 4500 or 6500 running IOS or the 3560/3750
series, you can configure ports to act as Layer 2 (switchport) ports or Layer 3 (rout-
ed) ports. To configure a port to act as a Layer 3 port, use the no switchport com-
mand to disable Layer 2 operation and enable Layer 3 operation.
Note When the switchport or no switchport command is issued, the port might be dis-
abled and then reenabled.