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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 10 Configuring Interface Characteristics
Using the Interface Command
When you configure an EtherChannel, you create a port-channel logical interface and assign an interface
to the EtherChannel. For Layer 2 interfaces, the logical interface is dynamically created. You manually
assign an interface to the EtherChannel by using the channel-group interface configuration command.
This command binds the physical and logical ports together. For more information, see Chapter 30,
“Configuring EtherChannels.”

Connecting Interfaces

Devices within a single VLAN can communicate directly through any switch. Ports in different VLANs
cannot exchange data without going through a routing device or routed interface.
With a standard Layer 2 switch, ports in different VLANs have to exchange information through a router.
In the configuration shown in Figure 10-1, when Host A in VLAN 20 sends data to Host B in VLAN 30,
it must go from Host A to the switch, to the router, back to the switch, and then to Host B.
Figure 10-1 Connecting VLANs with Layer 2 Switches
Using the Interface Command
To configure a physical interface (port), use the interface global configuration command to enter interface
configuration mode and to specify the interface type, slot, and number.
Type—Fast Ethernet (fastethernet or fa) for 10/100 Ethernet, Gigabit Ethernet (gigabitethernet or
gi), or LRE (longreachethernet or lo).
Slot—The slot number on the switch (always 0 on this switch).
Port number—The interface number on the switch. The port numbers always begin at 1, starting with
the leftmost port when facing the front of the switch, for example, fastethernet0/1, fastethernet0/2.
If there is more than one interface type (for example, 10/100 ports and Gigabit Ethernet ports), the
port number restarts with the second interface type: gigabitethernet0/1, gigabitethernet0/2.
Host A
Switch
Cisco router
VLAN 20
Host B
VLAN 30
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