CCNP路由题库中有6道题答案不明确，我附上个人理解，烦请各位解答。

xinxin_Ireland

各位好，有几道路由选择题比较迷惑，烦请各位协助解答。多谢。

79Refer to the exhibit. The networksetup is running the RIP routing protocol. Which two events will occurfollowing link failure between R2 andR3? (Choose two.)（论坛答案为AC，闫辉老师视频答案为AD。）

(图略）
A. R2 will advertisenetwork 192.168.2.0/27 with a hop count of 16 to R1.
B. R2 will not send any advertisements and will remove route192.168.2.0/27 from its routing table.

C. R1 will reply to R2 withthe advertisement for network 192.168.2.0/27 with a hop count of 16.

D. After communicationfails and after the hold-down timer expires, R1 will remove the 192.168.2.0/27 route from its routing table.

E. R3 will not accept any further updates from R2, due to thesplit-horizon loop prevention mechanism.

117 The enterprise network WAN link has been receiving several denial ofservice attacks from both IPv4 and IPv6 sources. Which three elementscan you use to identify an IPv6 packet via its header, in order to filter future attacks? (Choose three.)（论坛答案ACD，闫辉老师视频里说不清楚为什么选这三个，网友答案是BEF，其他网络答案为BEC。）
A. Traffic Class
B. Source address
C. Flow Label
D. Hop Limit
E. Destination Address
F. Fragment Offset

138 Other than a working EIGRPconfiguration, which option must be the same on all routersfor EIGRP authentication key rollover towork correctly? （论坛答案为D，网友答案为C）

A. SMTP
B. SNMP
C. Passwords
D. Time

我在网上看到这样一句话：“When using MD5 authentication keys, it is imperative thesite is in compliance with the NTP policies. Therouter has to know the time!”所以，还是应该选D.Time是吗？

191 Refer to Exhibit. Which two reasonsfor IP SLA tracking failure are likely true? (Choose Two.)(论坛答案为BE，网友答案为BC)

（图略）

                              

A. The source-interface is configured incorrectly.

B. The destination must be 172.30.30.2 for icmp-echo.

C. A route back to the R1LAN network is missing in R2.

D. The default route has wrong next hop IP address.

E. The threshold value iswrong.

Cisco 建议：当您配置IPSLA时，思科推荐这些默认值：

           1.Threshold(millisecs) ：5000

           2.Timeout(millisecs) ：5000

           3. Frequency(secs) ：60

题目所给图中配置的threshold 为500，所以，我认为选项E是正确的，对吗？

192 A network engineer enables OSPF ona Frame Relay WAN connection to various remote sites, but no OSPF adjacenciescome up. Which two actions are possible solutions for this issue? (Choose Two.)（论坛答案为AC，网友答案为AD）

A. Change the network type to point-to-multipointunder WAN interface.

B. Enable virtual links.

C. Change the network typeto nonbroadcast multipoint access.

D. Configure the neighborcommand under OSPF process for each remote site.

E. Ensure that the OSPF process number matches among all remotesites.

我很迷惑。neighbor命令在点到多点广播网络类型中，无用手工配置OSPF邻居吧。但在点到多点非广播模式中，需要手工配置OSPF邻居，因为Hello的组播包无法穿越FR环境。点到多点-当配置时帧中继多点子接口，OSPF对待它作为NBMA网络类型。

202 What is URPF checking first whenthe packet enters the interface? 或者是 When unicast reverse patchforwarding is configured on interface, which action does the interface takelist when it received a packet？（论坛答案为C，网友答案为A）

A. It check the ingressaccess list

B. It check the egress access list

C. Route available in FIB 或是It verifies a reverse patch via the FIB to thesource（patch应该是path吧？）

D. It verifies that the source has a valid CEF adjacency

其实，我也应该选C。当Unicast RPF在某个接口上启用，路由器检查所有进入此接口的数据包，确定其源IP地址和源接口在路由表中存在。这种“向后看”的能力只有当Ciscoexpress forwarding (CEF) 启用时才生效，因为其依赖于Forwarding InformationBase (FIB)，FIB是CEF生成的。

江南/sun

问了业内人士，117答案为BEF,192为AD

Rockyw

路过了解一下

vesim1

garylai56

138 is C

136170686

117题如果理解成从包头来区分IPv4和IPv6的数据包，就可以选ACD了，看了几遍总觉得这个题表述不清楚。

Shalltear

标记一下      

stone918

QUESTION 135
Refer to the following configuration command.
router(config)# ip nat inside source static tcp 172.16.10.8 8080 172.16.10.8 80
Which statement about the command is true?
A. Any packet that is received in the inside interface with a source IP port address of
172.16.10.8:80 is translated to 172.16.10.8:8080.
B. Any packet that is received in the inside interface with a source IP port address of
172.16.10.8:8080 is translated to 172.16.10.8:80.
C. The router accepts only a TCP connection from port 8080 and port 80 on IP address
172.16.10.8
D. Any packet that is received in the inside interface with a source IP address of 172.16.10.8
is redirected to port 8080 or port 80.
Correct Answer: A
这题怎么感觉应该选B呢

xinxin_Ireland

stone918 发表于 2017-3-5 10:03
QUESTION 135
Refer to the following configuration command.
router(config)# ip nat inside source st ...

我也觉得是B，但是答案给的是A。我很费解啊。。。。。。

田三三

stone918 发表于 2017-3-5 10:03
QUESTION 135
Refer to the following configuration command.
router(config)# ip nat inside source st ...

我也觉得选b

鸿午

江南/sun 发表于 2017-2-24 22:09
问了业内人士，117答案为BEF,192为AD

117原答案是对。
另外
IPv6
中也加入了几个字段：
 
1.
流量分类
----
该字段类似与
IPv4
中的服务类型。改该字段以区分业务编码点（
DSCP
）标记一个
IPv6
数据包，以此指明数据包应该如何处理。
 
2.
流标签
----
该字段用来标记
IPv6
数据包的一个流
 
3.
有效荷载长度
----
表示有效荷载长度。
 
4.
下一个包头
----
下一个包头类似与
IPv4
的协议号字段
 
5.
跳限制
----
和
IPv4
中一样，每过一条值减
1
，值为
0
时，数据包被丢弃，同时发送一条
ICMPv6
类
型
3
的消息（超时）到源节点。
 

鸿午

江南/sun 发表于 2017-2-24 22:09
问了业内人士，117答案为BEF,192为AD

192题正确答案AD
帧中继（
fram-relay
）网络属于非广播型多路访问，
 
       
而
OSPF
协议规定路由器之间的
Hello
包是通过组播来传输
 
    
（
组播也属于非广播类型）
因此帧中继上默认情况是无法运行
OSPF
协议的。
 
 
下面有
4
种解决方法：
 

 
方法一，手工设置
ospf
网络类型为广播型，在指定
fram-relay 
map
时设
置为
broadcast 
（
Fram-relay 
广播）
 

 
方法二，默认非广播类型，使用
neighbor
手工指定邻居，并且手工指定
DR
为中心路由器
 
（
fram-relay
非广播）
 

 
方法三，手工设置
OSPF
网络类型为：点到多点型广播型，在指定
fram-relay map
时设置为
broadcast 
（
fram-relay 
点对多点广播）
 

 
方法四：手工设置
OSPF
网络类型为：点到多点非广播，使用
neighbor
手工指定邻居