Trunk links should be configured statically whenever possible; however,
Catalyst switch ports run Dynamic Trunking Protocol (DTP) that can
automatically negotiate a trunk link. This Cisco proprietary protocol can
determine an operational trunking mode and protocol on a switch port when
connected to another device that is also capable of dynamic trunk negotiation.
A DTP mode can be configured to turn the protocol off or to instruct it
to negotiate a trunk link only under certain conditions as described in the
figure.
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NOTE:
General best practice is to set trunking to on and nonegotiate when a
trunk link is required. DTP should be turned off on links where trunking is not
intended.
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