To turn off dynamic trunking protocol (DTP) and use dot1q standard.
Sw2-3560#conf t Sw2-3560(config)#int range gi0/1-2 Sw2-3560(config-if-range)#switchport trunk encapsulation dot1q Sw2-3560(config-if-range)#switchport mode trunk Sw2-3560(config-if-range)#switchport nonegotiate Sw2-3560(config-if-range)#exit Sw2-3560(config)#
It is recommended to turn off trunking protocol and put vtp to transparent mode, this is because a newly introduced Catalyst switch may form undesired switch topology and if the newly introduced Catalyst switch has a vtp revision number higher than the current switch VTP revision then all vlan database of current switches will be overwritten.
