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Cisco IE 2000 Switch Software Configuration Guide
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Chapter 15 Configuring Interface Characteristics
Information About Configuring Interface Characteristics
Port-Based VLANs
A VLAN is a switched network that is logically segmented by function, team, or application, without
regard to the physical location of the users. For more information about VLANs, see the Chapter 17,
“Configuring VLANs.” Packets received on a port are forwarded only to ports that belong to the same
VLAN as the re ceiving port. Network devices in different VLANs cannot communicate with one another
without a Layer 3 device to route traffic between the VLANs.
VLAN partitions provide hard firewalls for traffic in the VLAN, and each VLAN has its own MAC
address table. A VLAN comes into existence when a local port is configured to be associated with the
VLAN, when the VLAN Trunking Protocol (VTP) learns of its existence from a neighbor on a trunk, or
when a user creates a VLAN.
To configure VLANs, use the vlan vlan-id global configuration command to enter VLAN configuration
mode. The VLAN configurations for normal-range VLANs (VLAN IDs 1 to 1005) are saved in the
VLAN database. If VTP is version 1 or 2, to configure extended-range VLANs (VLAN IDs 1006 to
4096), you must first set VTP mode to transparent. Extended-range VLANs created in transparent mode
are not added to the VLAN database but are saved in the switch running configuration. With VTP version
3, you can create extended-range VLANs in client or server mode. These VLANs are saved in the VLAN
database.
Add ports to a VLAN by using the switchport interface configuration commands:
Identify the interface.
For a trunk port, set trunk characteristics, and if desired, define the VLANs to which it can belong.
For an access port, set and define the VLAN to which it belongs.
Switch Ports
Switch ports are Layer 2-only interfaces associated with a physical p ort. A switch port can be an access
port, a trunk port, or a tunnel port. You can configure a port as an access port or trunk port or let the
Dynamic Trunking Protocol (DTP) operate on a per-port basis to set the switchport mode by negotiating
with the port on the other end of the link. Switch ports are us ed for managing the physical interface and
associated Layer 2 protocols.
Configure switch ports by using the switchport interface configuration commands. Use the switchport
command with no keywords to put an interface that is in Layer 3 mode into Layer 2 mode.
Note When you put an interface that is in Layer 3 mode into Layer 2 mode, the previous configuration
information related to the affected interface might be lost, and the interface is returned to its default
configuration.
For detailed information about configuring access port and trunk po rt characteristics, see Chapter 17,
“Configuring VLANs.”