TCP/IP 路由 卷一 習題 ospf

1. 什麼是OSPF鄰居

   從路由器的角度來說，鄰居是指直接在於該OSDF路由器相鄰的其他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. 什麼是OSPF鄰接關係？

   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的數據包的5種類型是什麼？每一種類型的用途是什麼？

    1. hello 

    2. 數據庫描述  - database description

    3. 鏈路狀態請求  link status request

    4. 鏈路狀態更新  link status update 

    5. 鏈路狀態確認  link status ack 

   
   

4. 什麼是LSA？怎麼樣區分一個LSA 和一個 OSPF 更新數據包的不同？

   
   

   
   

   路由器產生一個鏈路狀態通告來描述一個或多個目標網路。 OSPF的update 數據包將LSA從一個鄰居傳送至另外一個鄰居，雖然LSA在整個 OSPF 區域內廣播，但update 數據包不會離開單個的數據鏈路。 

   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的類型1到類型5，以及類型7分別是什麼？每一種類型的用途是什麼？

   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產生，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

什麼是鏈路狀態數據庫？鏈路狀態數據庫的同步是什麼意思？

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. 

數據庫同步保證一個區域內所有的路由器都有一致的鏈路狀態數據庫的過程

7. 什麼是缺省的HelloInternal？10 

8. 什麼是缺省的RouterDeadInterval？10×4 = 40s

9. 什麼是路由器ID？怎麼樣確定一個路由器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. 什麼是區域

     一個區域是指一個 OSPF子域，在區域內，所有的路由器都有一致的鏈路狀態數據庫

11. 區域0的含義是什麼？

     區域0 是骨幹區域，所有其他的區域必須通過主幹域來發送他們的區域內流量

12. 什麼是最大生存時間（MaxAge)?1 hours LSRefresh Time 30minutes  though as a keeplive for each LSA 

13 OSPF協議的4種路由器類型是什麼？

     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協議的4種路徑類型是什麼？

     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中網絡類型是什麼？

       point-to-point

       broadcst network 

       Nonbroadcast Multiaccess networks NBMA

       point-to-multipoint networks

       Virtual links 

16. 什麼是指定路由器DR？

      In NBMA network, 它代表這個NBMA  網絡來和其他的路由器進行連接。 

17. 在cisco 路由器上是怎樣計算一個接口的出站代價的？

cisco 公司使用的是缺省的10×8次方/BW ，表示爲一個整數，如果接口帶寬爲128kbit/s 

10*8次方/128Kbit/s= 781

接口爲100M 10*8次方/100000000=1 

18. 什麼是分段的區域？

如果一個區域內的一臺或者墮胎路由器不通過向區域外部發送數據包就不能向區域內的其他路由器發送數據包，那麼這個區域應該劃分子區域

19. 什麼是虛電路？

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

20. 末梢區域，完全末梢區域和非純末梢區域之間有什麼不同？

末梢區域， LSA 5 不能廣播

完全末梢：LSA 3,LSA4 LSA5 都不能廣播， 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網絡條目和OSPF路由條目之間有什麼不同之處？

OSPF網絡表項是路由表中的表項，描述了IP目標網絡，OSPF路由器表項是在一個單獨的路由表中的表項，該路由表只記錄了到達ABR和ASBR的路由

22. 爲什麼類型2的認證方式比類型1的認證方式更好？

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

23. LSA頭部中哪3段字段是用來區分不同的LSA的？另外,在LSA頭部中哪3個字段是用來區分相同的LSAde不同實類的？

類型/鏈路狀態ID 和通告路由器可以唯一的識別每個LSA

每個LSA的最新實例 老化時間按和序列號和校驗和