26. In Layer 2 topologies, spanning-tree failures can cause loops in the network. These unblocked loops can cause network failures because of excessive traffic. Which two Catalyst 6500 features can be used to limit excessive traffic during spanning-tree loop conditions? (Choose two.)
在2层的拓扑中，生成树发生故障会导致网络的环路。成环的网络中的流量可以导致网络的瘫痪。在6500交换机中哪两个功能可以防止生成树的环路过高的流量
A. loop guard 
B. storm control
C. storm suppression 
D. broadcast suppression 
E. BPDU guard Answer: BD 
 
27. Why does RSTP have a better convergence time than 802.1D?
为什么快速生成树协议收敛时间比802.1d的收敛时间更短
A. it is newer 
B. it has smaller timers 
C. it has less overhead 
D. it is not timer-based 
Answer: D   

28. Loop guard and UniDirectional Link Detection both protect against Layer 2 STP loops. In which two ways does loop guard differ from UDLD in loop detection and prevention? (Choose two.)  
环路检测和单向链路检测，保证2层STP没有环路。这两种做法不同于UDLD中的环路检测 吗？   
A. Loop guard can be used with root guard simultaneously on the same port on the same VLAN while UDLD cannot.   
B. UDLD protects against STP failures caused by cabling problems that create one-way links.   
UDLD 是为了防止电缆故障，造成一个单向故障   
C. Loop guard detects and protects against duplicate packets being received and transmitted on different ports.   
D. UDLD protects against unidirectional cabling problems on copper and fiber media. E. Loop guard protects against STP failures caused by problems that result in the loss of BPDUs from a designated switch port.  
Answer: BE    
    
29. Refer to exhibits 1 and 2. In exhibit 1, all users on the LAN segment use router A as the active HSRP router. Router B is the standby router for the HSRP. In exhibit 2, the network management team reported that there is no utilization on the WAN link B. To solve this problem, you decide to change the logical topology of your LAN, but you are not sure about what changes must be made. You must manage HSRP or change it to another protocol in order to provide the most scalable design, automatic redundancy, and load balancing. Which one of these actions would be the best choice?

如图所示，在1组 所有用户是在使用网络中开启了HSRP路由器A和主用路由路由器B是备 用路由器。在2组 网络小组报告网络用户没有使用b的WAN口。要解决这个问题，你决心改 变网络逻辑拓扑，但是你不确定必须这样做。你必须使用HSRP或者使用其他协议来实现挽 网络可扩展性，自动冗余，自动负载。下面哪一个是最好的选择？

A. Use MHSRP, with three users using router A as the default gateway and three users using router B as the default gateway. B. Keep HSRP and activate PBR to redirect half of the traffic to the other WAN link. C. Use the backup interface on the WAN link B to provide load balancing for all users. D. Use GLBP instead, because it provides you with up to three MAC addresses for the same default gateway virtual IP address. E. Use GLBP instead, because it provides you with up to four MAC addresses for the same default gateway virtual IP address.

30. The network administrator wants to enable an EtherChannel between two switches in "on" mode. The administrator connects the cables and enables the interfaces, but while configuring the EtherChannel in the first switch, a spanning-tree loop was detected. Which two of these procedures can avoid this problem? (Choose two.)

网络管理员想在”on”模式下在两台交换机之间开启以太通道， 管理员用线路连接在交换机的 接口上。但是在配置第一台交换机的以太通道时。有一个生成树环路已经产生了。那两个措 施能够避免这个问题？

A. Configure the EtherChannel as "desirable" first. 配置以太通道的模式为“desirable” B. Assign all interfaces to the same VLAN. C. Disable PortFast on the interfaces in the EtherChannels. D. Disable all interfaces first. F. Fix cabling problems.
Answer: AD