原题：

　　What is the basic characteristic of switches and hubs?

　　A. Hubs cannot filter frames.

　　B. Using hubs is costly with regard to bandwidth availability.

　　C. Switches do and can not forward broadcasts.

　　D. Switches are more efficient than hubs in processing frames.

　　E. Switches increase the number of collision domains in the network.

　　汉意：

　　交换机与集线器的基本特征是什么？

　　正确答案：E

　　解释：

　　交换机增加网络中冲突域的数量。

　　注意：

　　交换机在内部处理中有一些不同类型的变量，尽管现在的交换机基本上都使用store-and-forward，但是大部分思科交换机，至少支持以下三种不同类型中的一种。

　　• Store-and-forward -The switch fully receives all bits in the frame (store) before forwarding the frame (forward).

　　• Cut-through - The switch performs the address table lookup as soon as the destination address field in the header is received.

　　• Fragment-free - This performs like cut-through switching, but the switch waits for 64 bytes to be received before forwarding the first bytes of the outgoing frame.

　　参考资料：

　　Sybex CCNA 4.0 640-801

　　CCNA Self-Study CCNA ICND exam certification Guide(Ciscopress,ISBN 1-58720-083-x)