14-14
Cisco IE 3010 Switch Software Configuration Guide
OL-23145-01
Chapter 14 Configuring VLANs
Configuring VLAN Trunks
For more details about the show command options and explanations of output fields, see the command
reference for this release.
Configuring VLAN Trunks
These sections contain this conceptual information:
Trunking Overview, page 14-14
Default Layer 2 Ethernet Interface VLAN Configuration, page 14-16
Configuring an Ethernet Interface as a Trunk Port, page 14-16
Configuring Trunk Ports for Load Sharing, page 14-20

Trunking Overview

A trunk is a point-to-point link between one or more Ethernet switch interfaces and another networking device
such as a router or a switch. Ethernet trunks carry the traffic of multiple VLANs over a single link, and you
can extend the VLANs across an entire network.
You can configure a trunk on a single Ethernet interface or on an EtherChannel bundl e. For more
information about EtherChannel, see Chapter 34, “Configuring EtherChannels and Li nk-State
Trackin g.”
Ethernet trunk interfaces support different trunking modes (see Ta ble 14-4 ). You can set an interface as
trunking or nontrunking or to negotiate trunking with the neighboring interface. To autonegotiate
trunking, the interfaces must be in the same VTP domain.
Trunk negotiation is managed by the Dynamic Trunking Protocol (DTP), which is a Point-to-Point
Protocol. However, some internetworking devices might forward DTP frames improperly, which could
cause misconfigurations.
To avoid this, you should configure interfaces connected to devices that do not support DTP to not
forward DTP frames, that is, to turn off DTP.
If you do not intend to trunk across those links, use the switchport mode access interface
configuration command to disable trunking.
To enable trunking to a device that does not support DTP, use the switchport mode trunk and
switchport nonegotiate interface configuration commands to cause the interface to become a trunk
but to not generate DTP frames.
Note DTP is not supported on private-VLAN ports or tunnel ports.