水平分割及几个题库的问题求解释

吸引力依旧

QUESTION 100

Refer to the exhibit. In the communication between host 1 and host 2 over the point-to-point WAN, which protocol or technology is represented by dashed line A?

A. IP B. T1 C. PPP D. IEEE 802.3

这个没看明白到底咋回事，IP不是网络层的么，怎么虚线A就代表了，难道不是物理层么虚线A。。。

QUESTION 526

Refer to the exhibit.The network shown in the exhibit is running the RIPv2 routing protocol.The network has converged,and the routers in this network are functioning properly .The FastEthernet0/0 interface on R1 goes down.In which two ways will the routers in this network respond to this change?(choose two)

A. R1 will send LSAs to R2 and R3 informing them of this change, and then all routers will send periodic updates at an increased rate until the network again converges.

B. Because of the split-horizon rule, router R2 will be prevented from sending erroneous information to R1 about connectivity to the 192.168.1.0 network.

C. When router R2 learns from R1 that the link to the 192.168.1.0 network has been lost, R2 will respond by sending a route back to R1 with an infinite metric to the network.

D. Routers R2 and R3 mark the route as inaccessible and will not accept any further routing updates from R1 until their hold-down timers expire.

E. All routers will reference their topology database to determine if any backup routes to the 192.168.1.0 network are known

题库上只解释了水平分割的那个，C是怎么回事呢？

水平分割是不向发送出路由信息的那个口往回发送路由更新么？那么如果后面的网络上增加或删除新网段，这个路由是不是也收不到相应的路由更新呢？还是说这个水平分割也有一定的时间来控制呢？不太明白，求解释~

2008luyi

第1题主机1和主机2不在同一网段，跨网段通信必须依靠IP层协议。T1是一种广域网链路，PPP是虚线C的封装，如果1和2在同一网段就使用802.3。
第2题的C是在说“反向下毒”的意思，“反向下毒”不受水平分割限制。

小乔

IP是指网络协议  不是IP地址
第二题C 就是路由中毒的过程