单项选择题 While using a packet analyzer， you notice four additional bytes being added to the packets in the  Company network.  Which protocol inserts a four byte tag into the Ethernet frame and recalculates  CRC value？  （）

单项选择题 You need to configure a new Company switch for trunking.  Which switch command enables a  trunking protocol that appends a four byte CRC to the packet？（）

单项选择题 Switch R1 has been configured with DTP using the desirable option.  Which statement describes  Dynamic Trunking Protocol （DTP） desirable mode？（）