If you are implementing VLAN trunking, which additional configuration parameter should be added
to the trunking configuration?

A.
no switchport mode access

B.
no switchport trunk native VLAN 1

C.
switchport mode DTP

D.
switchport nonnegotiate

Explanation:
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/layer2.
html
Layer 2 LAN Port Modes
Table 17-2 lists the Layer 2 LAN port modes and describes how they function on LAN ports.
switchport mode access Puts the LAN port into permanent nontrunking mode and negotiates to

convert the link into a nontrunk link. The LAN port becomes a nontrunk port even if the
neighboring LAN port does not agree to the change.
switchport mode dynamic desirable
Makes the LAN port actively attempt to convert the link to a trunk link. The LAN port becomes a
trunk port if the neighboring LAN port is set to trunk, desirable, or auto mode. This is the default
mode for all LAN ports.
switchport mode dynamic auto
Makes the LAN port willing to convert the link to a trunk link. The LAN port becomes a trunk port if
the neighboring LAN port is set to trunk or desirable mode.
switchport mode trunk Puts the LAN port into permanent trunking mode and negotiates to convert
the link into a trunk link. The LAN port becomes a trunk port even if the neighboring port does not
agree to the change.
switchport nonegotiate
Puts the LAN port into permanent trunking mode but prevents the port from generating DTP
frames. You must configure the neighboring port manually as a trunk port to establish a trunk link.