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开放链路最短优先

《 网络互联技术 》. 开放链路最短优先. Open Shortest Path First. 计算机通信教研室 周成纲. 链路状态协议（ Link-State Protocols ）. OSPF 概述（ OSPF Overview ）. 分层设计（ Hierarchical Design ）. 1. 大的 OSPF 网络采用分层设计，所有区域连接到主干区域。

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开放链路最短优先

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  1. 《网络互联技术》 开放链路最短优先 Open Shortest Path First 计算机通信教研室 周成纲

  2. 链路状态协议（Link-State Protocols）

  3. OSPF概述（OSPF Overview）

  4. 分层设计（Hierarchical Design） • 1.大的OSPF网络采用分层设计，所有区域连接到主干区域。 • Large OSPF networks use a hierarchical design. Multiple areas connect to a distribution area, area 0, also called the backbone. • 2.好处（benefit）： （1）减少路由更新（reduces routing overhead） （2） 加速收敛（speeds up convergence） （3）限制不稳定到一个区域（confines network instability to an area） （4）提高网络性能（improves performance）

  5. OSPF术语（OSPF Terminology）

  6. OSPF数据包类型（OSPF Packet Types）

  7. OSPF数据包头格式（OSPF Packet Header Format）

  8. OSPF操作（OSPF Operation） • 1.建立邻接关系 Establish router adjacencies 2.必要的进行DR选举 Elect the DR / BDR ( if necessary ) 3.发现路由 Discover routes 4.选择相应的路由 Select appropriate routes 5.维护路由信息 Maintain routing information

  9. 邻居关系（Neighborship） *标记的在邻居路由器上必须匹配

  10. 建立双向通信（Establishing Bidirectional Communication）

  11. 建立双向通信（Establishing Bidirectional Communication）

  12. 建立双向通信（Establishing Bidirectional Communication）

  13. 建立双向通信（Establishing Bidirectional Communication）

  14. 查找网络路由（Discovering the Network Routes）

  15. 查找网络路由（Discovering the Network Routes）

  16. 增加链路状态条目（Adding the Link-State Entries）

  17. 增加链路状态条目（Adding the Link-State Entries）

  18. 增加链路状态条目（Adding the Link-State Entries）

  19. 维护路由信息（Maintaining Routing Information） • 路由器用224.0.0.6通知DR • Router A notifies all OSPF DRs on 224.0.0.6

  20. 维护路由信息（Maintaining Routing Information） • DR利用组播地址224.0.0.5通知其它路由器 • DR notifies others on 224.0.0.5

  21. 维护路由信息（Maintaining Routing Information）

  22. 维护路由信息（Maintaining Routing Information）

  23. 维护路由信息（Maintaining Routing Information）

  24. OSPF网络类型（OSPF Network Types） 广播Broadcast Multiaccess 非广播Nonbroadcast Multiaccess Frame Relay X.25 点到点Point-to-Point 点到多点Point-to-Multipoint

  25. 点到点链路（Point-to-Point Links） • 1.不进行DR选举 • No DR or BDR election required • 2. OSPF自动检测这种接口类型 • OSPF autodetects this interface type

  26. 广播型多路访问网络（Multiaccess Broadcast Network） • 1.进行DR选举 • DR and BDR selection required • 2.邻居只与DR和DBR形成邻接关系 • All neighbor routers form full adjacencies with the DR and BDR only

  27. 选举DR和BDR（Electing the DR and BDR） • 1.最高接口优先级的路由器被选成DR • The router with the highest OSPF priority is selected as the DR. • 2.最高路由器ID的路由器被选举成DR • Use the OSPF router ID as the tie breaker. • 3.DR选举不具有抢占性 • The DR election is nonpreemptive.

  28. 设置接口优先级（Setting Interface Priority） Router(config-if)# ip ospf priority number • 1. 不同的接口可以指定不同的值 • Different interfaces on a router may be assigned different values. • 2. 接口优先级默认为1,取值范围是0-255 • The default priority is 1. The range is from 0 to 255. • 3. 接口优先级为0表示不参加DR选举 • 0 means the router is a DROTHER; it can’t be the DR or BDR.

  29. OSPF基本配置（Configuring Basic OSPF） Router(config)# router ospf process-id • 启动路由进程 • Turns on one or more OSPF routing processes Router(config-router)# network address inverse-maskarea [area-id] • 用network命令ospf运行的接口，并将网络指定到特定的区域 • Router OSPF subordinate command that defines the interfaces (by network number) that OSPF will run on. Each network number must be defined to a specific area.

  30. OSPF配置实例（Configuring OSPF Example）

  31. 验证ospf配置（Verifying OSPF Operation） show ip protocols Show ip ospf neighbor Show ip ospf database Show ip route Show ip ospf Show ip ospf interface Debug ip ospf adj Debug ip ospf event

  32. 确定OSPF路由器ID（OSPF Router ID） • 1. 通过router-id命令指定的最为优先 • An OSPF router-id command can override OSPF router ID. • 2. 最高的环回接口地址次之 • A loopback interface can override OSPF router ID. It is the highest IP address of any active loopback interface. • 3. 最后是最高活动的物理接口的IP地址 • the router ID is the highest IP address on an active interface at the moment of OSPF process startup. 为了稳定，命令或环回接口被推荐 The loopback or router-id command is recommended for stability.

  33. 环回接口（Loopback Interfaces） Router(config)# interface loopback 0 Router(config-if)# ip address 172.16.17.5 255.255.255.255 • 如果ospf路由进程已经启动，必须重新清除ospf进程，新的路由器ID才生效。 • If the OSPF process is already running, the OSPF process must be cleared before the new router-id command will take effect.

  34. OSPF router-id 命令（OSPF router-id command） Router(config-router)# router-id ip-address • 这是路由进程下的子命令 • This command is subordinate to the router-id ospf command. • 用clear ip ospf process命令可以使得配置生效。 • If this command is used on an OSPF process that is already active, then the new router ID is used at the next reload or at a manual OSPF process restart using the clear ip ospf process command. Router(config-if)# router ospf 1 Router(config-router)# router-id 172.16.1.1

  35. 显示路由器ID（OSPF Router ID Verification） RouterA# show ip ospf Routing Process "ospf 1" with ID 1.1.3.1 Supports only single TOS(TOS0) routes SPF schedule delay 5 secs, Hold time between two SPFs 10 secs Number of DCbitless external LSA 0 Number of DoNotAge external LSA 0 Number of areas in this router is 1. 1 normal 0 stub 0 nssa Area BACKBONE(0) (Active) Number of interfaces in this area is 2 Area has no authentication SPF algorithm executed 10 times Area ranges are Link State Update Interval is 00:30:00 and due in 0:07:16 Link State Age Interval is 00:20:00 and due in 00:07:15 Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0

  36. 配置OSPF计时器（Configuring OSPF Timers） OSPF计时器在接口下配置

  37. 配置OSPF认证（Configuring OSPF Authentication）

  38. 维护大的OSPF网络的问题（Issues with Maintaining a Large OSPF Network）

  39. 解决方案：OSPF分层路由（The Solution: OSPF Hierarchical Routing）

  40. OSPF路由器类型（Types of OSPF Routers）

  41. OSPF路由器类型（Types of OSPF Routers）

  42. OSPF路由器类型（Types of OSPF Routers）

  43. OSPF路由器类型（Types of OSPF Routers）

  44. OSPF路由器类型（Types of OSPF Routers）

  45. OSPF路由的类型（Types of Routes）

  46. E1和E2路由 cost计算（Calculating Costs for E1 and E2 Routes）

  47. E1和E2路由 cost计算（Calculating Costs for E1 and E2 Routes）

  48. 配置路由汇总（Configuring Route Summarization） Router(config-router)# area area-id range address mask • Consolidates inter-area (IA) routes on an ABR Router(config-router)# summary-address address mask [not-advertise] [tag tag] • Consolidates external routes, usually on an ASBR

  49. 在ABR配置路由汇总实例（Route Summarization Configuration Example at ABR）

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