TCP/IP 路由 卷一 习题 ospf

1. 什么是OSPF邻居

   从路由器的角度来说，邻居是指直接在于该OSDF路由器相邻的其他OSPF路由器

   From the perspective of an OSPF router, a neighbor is another OSPF router that is directly attached to one of the first router's connected links. 

2. 什么是OSPF邻接关系？

   an OSPF adjacency is a conceptual link to a neighbor over which LSAs can be sent 

   
   

   There are the four steps

   Neighbor discovery 

   Bidirectional communication, this communication is accomplished when two neighbors list each other's Rotuer IDs in their hello packets. 

   Database synchronization, database description, link state request, link state update, link state acknowledgement packets are exchagned to ensure that both neighbors have idential information in their link-state databases, for the purposes of this process, one neighbor will become the master and the other will become the slave, as the name implies, the master will control the exchange of database description packets. 

   
   

3. OSPF的数据包的5种类型是什么？每一种类型的用途是什么？

    1. hello 

    2. 数据库描述  - database description

    3. 链路状态请求  link status request

    4. 链路状态更新  link status update 

    5. 链路状态确认  link status ack 

   
   

4. 什么是LSA？怎么样区分一个LSA 和一个 OSPF 更新数据包的不同？

   
   

   
   

   路由器产生一个链路状态通告来描述一个或多个目标网路。 OSPF的update 数据包将LSA从一个邻居传送至另外一个邻居，虽然LSA在整个 OSPF 区域内广播，但update 数据包不会离开单个的数据链路。 

   A router originates a link-state advertisment to describe one or more destinations, An ospf update packets transports LSAs from one neighbor to another, although LSAs are flooded throughout an area or OSPF domain, update pckets never levae a data link. 
   

5. LSA的类型1到类型5，以及类型7分别是什么？每一种类型的用途是什么？

   Router LSA

   
   

   Network LSA

   A DR originates a Network LSA to represent a multi-access network and all attached routers 

   
   

   Network summary LSA 

   Originated by ABR to describe inter-area destinations. 

   
   

 ASBR LSA

 由abr产生，ASBR summary lsa are identical to network summary LSAs except that the destination they advertise is an ASBR, not a network 

AS External LSA

group membership LSA
NSSA external LSA

are originated by automous system boundary routers within not-so-stubby areas. 

External Attributes LSA

什么是链路状态数据库？链路状态数据库的同步是什么意思？

All valid LSAs received by a router are stored in its link-state database, the collected LSAs will describe a graph of the area topoloby. 

数据库同步保证一个区域内所有的路由器都有一致的链路状态数据库的过程

7. 什么是缺省的HelloInternal？10 

8. 什么是缺省的RouterDeadInterval？10×4 = 40s

9. 什么是路由器ID？怎么样确定一个路由器ID？

A router ID is an address by which an OSPF router identifies itsself. It is eigher numerically highest IP address of allthe routers's loopback interface. or if no loopback address, the highest IP address on LAN interafce, it can also be manually configured. 

10. 什么是区域

     一个区域是指一个 OSPF子域，在区域内，所有的路由器都有一致的链路状态数据库

11. 区域0的含义是什么？

     区域0 是骨干区域，所有其他的区域必须通过主干域来发送他们的区域内流量

12. 什么是最大生存时间（MaxAge)?1 hours LSRefresh Time 30minutes  though as a keeplive for each LSA 

13 OSPF协议的4种路由器类型是什么？

     Internal routers, whose OSPF interfaces all belong to the same area. 

     Backbone Routers, which are internal Routers in Area 0

     Area Border routers, which have OSPF interafaces in more than one area. 

     Autonomous system boundary routers, which advertise external routes into the OSPF domain 

14 OSPF协议的4种路径类型是什么？

     Intra-area paths 

     Inter-area paths

     Type 1 external paths (exteranl_cost+ospf cost)

     Type 2 external paths (only external cost)

15 OSPF的5中网络类型是什么？

       point-to-point

       broadcst network 

       Nonbroadcast Multiaccess networks NBMA

       point-to-multipoint networks

       Virtual links 

16. 什么是指定路由器DR？

      In NBMA network, 它代表这个NBMA  网络来和其他的路由器进行连接。 

17. 在cisco 路由器上是怎样计算一个接口的出站代价的？

cisco 公司使用的是缺省的10×8次方/BW ，表示为一个整数，如果接口带宽为128kbit/s 

10*8次方/128Kbit/s= 781

接口为100M 10*8次方/100000000=1 

18. 什么是分段的区域？

如果一个区域内的一台或者堕胎路由器不通过向区域外部发送数据包就不能向区域内的其他路由器发送数据包，那么这个区域应该划分子区域

19. 什么是虚电路？

A virtual link is a link to the backbone through a non-backbone area. 

20. 末梢区域，完全末梢区域和非纯末梢区域之间有什么不同？

末梢区域， LSA 5 不能广播

完全末梢：LSA 3,LSA4 LSA5 都不能广播， with the exception type 3 LSAs to advertise a default route 

非完全末梢：Not-so_stubby areas are areas through which external destinations are advertised into the OSPF domain, but into which no type 5 LSAs are sent by the ABR. 

21. OSPF网络条目和OSPF路由条目之间有什么不同之处？

OSPF网络表项是路由表中的表项，描述了IP目标网络，OSPF路由器表项是在一个单独的路由表中的表项，该路由表只记录了到达ABR和ASBR的路由

22. 为什么类型2的认证方式比类型1的认证方式更好？

Type 2 authentication use MD5 encryption, Type 1 use clear text passwors. 

23. LSA头部中哪3段字段是用来区分不同的LSA的？另外,在LSA头部中哪3个字段是用来区分相同的LSAde不同实类的？

类型/链路状态ID 和通告路由器可以唯一的识别每个LSA

每个LSA的最新实例 老化时间按和序列号和校验和