DTP
DTP（dynamic trunking protocol）動態鏈路聚集協議
DTP是 Cisco私有點到點協議，用來動態協商端口類型為Access或者Trunk，
DTP(動態鏈路聚集協議)
。要完成自動協商，2端口必須在同一個VTPdomain中。每30s發送一次DTP的frame. 該協議僅在交換機間協商。端口DTP模式
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配置DTP
Switch(config-if)#switchportmode ?
access Set trunking mode to ACCESS unconditionally
dynamic Settrunking mode to dynamically negotiate access or trunk mode
trunk Set trunking mode to TRUNKunconditionally
在動態模式下關閉協商
Switch(config-if)#switchport nonegotiate
Command rejected: Conflict between 'nonegotiate'and 'dynamic' status.
驗證DTP
Switch#showinterface switchport
Name:Fa0/1
Switchport:Enabled
Administrative Mode: dynamic auto
OperationalMode: down
Administrative Trunking Encapsulation: dot1q
OperationalTrunking Encapsulation: native
Negotiationof Trunking: On