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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 10 Configuring Interface Characteristics
Understanding Interface Types
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
Packets received on a port are forwarded only to ports that belong to the same
VLAN as the receiving 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 normal-range VLANs (VLAN IDs 1 to 1005), use the vlan vlan-id global configuration
command to enter config-vlan mode or the vlan database privileged EXEC command to enter VLAN
configuration mode. The VLAN configurations for VLAN IDs 1 to 1005 are saved in the VLAN
database. To configure extended-range VLANs (VLAN IDs 1006 to 4094), you must use config-vlan
mode with VTP mode set to transparent. Extended-range VLANs are not added to the VLAN database.
When VTP mode is transparent, the VTP and VLAN configuration is saved in the switch running
configuration, and you can save it in the switch startup configuration file by entering the copy
running-config startup-config privileged EXEC command.
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.
•
For a tunnel port, set and define the VLAN ID for the customer-specific VLAN tag. See
“Configuring 802.1Q and Layer 2 Protocol Tunneling.”
Switch Ports
Switch ports are Layer 2-only interfaces associated with a physical port. 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 determine if a switch port should be an
access port or a trunk port by negotiating with the port on the other end of the link. You must manually
configure tunnel ports as part of an asymmetric link connected to an 802.1Q trunk port. Switch ports are
used for managing the physical interface and associated Layer 2 protocols and do not handle routing or
bridging.
Configure switch ports by using the switchport interface configuration commands. For detailed
information about configuring access port and trunk port characteristics, see
For more information about tunnel ports, see