Cisco Catalyst 2960 Command Reference Manual page 579

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Chapter 2 Catalyst 3750 Switch Cisco IOS Commands

To autonegotiate trunking, the interfaces must be in the same VLAN Trunking Protocol (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, which turns 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.

Access ports and trunk ports are mutually exclusive.

The IEEE 802.1x feature interacts with switchport modes in these ways:

If you try to enable IEEE 802.1x on a trunk port, an error message appears, and IEEE 802.1x is not

enabled. If you try to change the mode of an IEEE 802.1x-enabled port to trunk, the port mode is

not changed.

If you try to enable IEEE 802.1x on a port set to dynamic auto or dynamic desirable, an error

message appears, and IEEE 802.1x is not enabled. If you try to change the mode of an

IEEE 802.1x-enabled port to dynamic auto or dynamic desirable, the port mode is not changed.

If you try to enable IEEE 802.1x on a dynamic-access (VLAN Query Protocol [VQP]) port, an error

message appears, and IEEE 802.1x is not enabled. If you try to change an IEEE 802.1x-enabled port

to dynamic VLAN assignment, an error message appears, and the VLAN configuration is not

Catalyst 2960 Switch Command Reference

switchport mode

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