Which statement about vlan operation on cisco catalyst switches is true?

A、 when a packet is received from an 802．1Q trunk,the vlan id can be determined from the source MAC address table．
B、 unkown unicast frames are retransmitted only to the ports that belong to the same vlan
C、 ports between switches should be configured in access mode so that vlans can span across the ports
D、 broadcast and multicast frames are retransmitted to ports that are configured on different vlan．

【正确答案】 B

【答案解析】A通过源mac地址确定vlan，不正确；
B未知单播帧只在本vlan传播，正确；
C交换机之间应该设置为trunk；
Dvlan能分割广播域，广播不能跨vlan传输。