21. Which of these correctly identifies a difference between the way BPDUs are handled by 802.1w and 802.1D? 哪个是在802.1W和802.1D协议对于BPDU信息的差异

A. 802.1D bridges do not relay BPDUs. B. 802.1w bridges do not relay BPDUs. C. 802.1D bridges only relay BPDUs received from the root.

　　因为他不基于计时器

　　802.1D桥只中转根桥发出的BPDU信息

　　D. 802.1w bridges only relay BPDUs received from the root.

　　Answer: C

　　22. Which three of these statements about Dynamic Trunking Protocol are correct? (Choose three.) 对于动态中继协议，下面哪三个是正确的 A. It supports autonegotiation for both ISL and IEEE 802.1Q trunks.

　　支持在ISL协议和802.1Q协议的自动协商

　　B. It must be disabled on an interface if you do not want the interface to work as a trunk or start negotiation to become a trunk.

　　如果你不想让一个接口成为trunk或开始协商成trunk，那么必须禁用它

　　C. It is a point-to-multipoint protocol. D. It is a point-to-point protocol. 需要在一个点到点的协议上使用 E. It is not supported on private VLAN ports or tunneling ports.

　　Answer: ABD

　　23. You are designing your network to be able to use trunks. As part of this process you are comparing the ISL and 802.1Q encapsulation options. All of these statements about the two encapsulation options are correct except which one?

　　你正在设计一个使用trunk的网络，你要比较使用ISL和802.1Q。对于这两种封装描述正确的 是哪个?

　　A. Both support normal and extended VLAN ranges. B. ISL is a Cisco proprietary encapsulation method and 802.1Q is an IEEE standard. C. ISL encapsulates the original frame. D. Both support native VLANs.

　　Answer: D

　　24. Refer to the exhibit. From the MAC addresses shown in the command output, to which two ports is the multicast stream 225.230.57.199 being forwarded on this switch? (Choose two.)

　　他们都支持本征VLAN

　　E. 802.1Q does not encapsulate the original frame.

　　如图所示，这是显示MAC地址库的命令的输出，在这个交换机那两个端口是组播 225.230.57.199的转发端口?

　　A. Fa6/28 B. Fa7/20 C. Gi3/7 D. Fa4/2 E. Fa4/14 F. Fa4/38 G. Fa6/28 H. Fa5/7

　　Answer: CE

　　25. You are about to migrate a customer network to use a VSS. Which of these statements is true about a VSS? 你要把网络升级为使用VSS,关于VSS的描述哪个是正确的 A. The VSS switch must be the root bridge for all VLANs and is automatically designated. B. The VSS switch is defined in RFC 4318 as a managed object. C. The PAgP+ or LACP protocols are used to maintain the operational state of the VSS devices.

　　PagP或LacP协议使用VSS设备

　　D. A VSS interoperates with a virtual port channel. E. The 802.1Q or ISL protocols are used to maintain the operational state of the VSS devices. F. A VSS increases the size of the spanning-tree domain.

　　Answer: C