OSPF的HELLO包!

快乐孤儿

<P>QUESTION NO: 14<BR>On the topic of the OSPF hello protocol; which of the statements below are true?<BR>(Select two answer choices)<BR>A. The OSPF Hello protocol provides dynamic neighbor discovery.<BR>B. The OSPF Hello protocol detects unreachable neighbors in 90 second intervals.<BR>C. The OSPF Hello protocol maintains neighbor relationships.<BR>D. The OSPF Hello protocol negotiates the correct parameters between neighboring<BR>interfaces.<BR>E. The OSPF Hello protocol uses timers to elect the router with the fastest links at<BR>the designated router.<BR>F. The OSPF Hello protocol broadcast hello packets throughout the internetwork to<BR>discover all routers that are running OSPF.</P><P>&nbsp;</P><P>答案选AC,</P><P>D可以吗?能不能详细讲解一下HELLO包的作用呢?</P>

王晓强

<P>D是不可以的。Hello协议只能交换相邻接口的参数，一致的话就继续通信，不一致就停止通信，而不会negotiates协商。这个主要是对协商的理解，Hello协议是带着自己本接口的固定参数跟对方接口进行比较，一致最好，不一致拉倒！不为了一致而协商而改变。<FONT color=#ff0033>H e l l o协议的责任是发现邻居并维持邻居关系。H e l l o包被周期地发向路由器<BR>接口，以网络类型为根据。H e l l o协议还担负着在多路访问网络中挑选出D R。</FONT>就这题而言，正确的就是Hello协议的作用了，来看看错在哪里。Hello协议的好几个时间参数跟它的网络类型有关，不是题中B选项描述的！E选项说在DR上Hello协议使用计时器来选择带有最快链路的路由器，Hello协议没那么好用，OSPF里也没有这类相关的描述，不选！F选项说Hello包throughout the internetwork ，那互联网就完蛋了，不选！</P>

快乐孤儿

<P>明白了...对HELLO包的认识又深入了一些,</P><P>看来还要把书的有关内容再看一次,谢谢</P>