10-7
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 10 Configuring LAN Ports for Layer 2 Switching
Configuring LAN Interfaces for Layer 2 Switching
Note Use the default interface {ethernet | fastethernet | gigabitethernet | tengigabitethernet} slot/port
command to revert an interface to its default configuration.
Configuring a LAN Port for Layer 2 Switching
To configure a LAN port for Layer 2 switching, perform this task:
After you enter the switchport command, the default mode is switchport mode dynamic desirable. If
the neighboring port supports trunking and is configured to allow trunking, the link becomes a Layer 2
trunk when you enter the switchport command. By default, LAN trunk ports negotiate encapsulation. If
the neighboring port supports ISL and 802.1Q encapsulation and both ports are set to negotiate the
encapsulation type, the trunk uses ISL encapsulation (10-Gigabit Ethernet ports do not support ISL
encapsulation).
Note When using the switchport command, if a port configured for Layer 3 is now configured for Layer 2,
the configuration for Layer 3 is retained in the memory but not in the running configuration and is
applied to the port whenever the port switches back to Layer 3. Also, if a port configured for Layer 2 is
now configured for Layer 3, the configuration for Layer 2 is retained in the memory but not in the
running configuration and is applied to the port whenever the port switches back to Layer 2. To restore
the default configuration of the port in the memory and in the running configuration, use the default
interface command. To avoid potential issues while changing the role of a port using the switchport
command, shut down the interface before applying the switchport command.
Command Purpose
Step 1
Router(config)# interface
type
1
slot/port
1. type = ethernet, fastethernet, gigabitethernet, or tengigabitethernet
Selects the LAN port to configure.
Step 2
Router(config-if)# shutdown
(Optional) Shuts down the interface to prevent traffic flow
until configuration is complete.
Step 3
Router(config-if)# switchport
Configures the LAN port for Layer 2 switching.
Note Yo u m us t e n te r t he switchport command once
without any keywords to configure the LAN port
as a Layer 2 port before you can enter additional
switchport commands with keywords.
Router(config-if)# no switchport
Clears Layer 2 LAN port configuration.
Step 4
Router(config-if)# no shutdown
Activates the interface. (Required only if you shut down
the interface.)
Step 5
Router(config-if)# end
Exits configuration mode.
Step 6
Router# show running-config interface
[
type
1
slot/port
]
Displays the running configuration of the interface.
Step 7
Router# show interfaces [
type
1
slot/port
]
switchport
Displays the switch port configuration of the interface.
Step 8
Router# show interfaces [
type
1
slot/port
] trunk
Displays the trunk configuration of the interface.
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