DTP
DTP（dynamic trunking protocol）动态链路聚集协议
DTP是 Cisco私有点到点协议，用来动态协商端口类型为Access或者Trunk，
DTP(动态链路聚集协议)
。要完成自动协商，2端口必须在同一个VTPdomain中。每30s发送一次DTP的frame. 该协议仅在交换机间协商。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
在动态模式下关闭协商
Switch(config-if)#switchport nonegotiate
Command rejected: Conflict between 'nonegotiate'and 'dynamic' status.
验证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