OSPF虚拟链路

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1 OSPF 虚拟链路 Contents Introduction Prerequisites Requirements Components Used Conventions Configure Network Diagram 配置虚链路如何运行计算最短路径使用而不是虚链路的一个 GRE 封装隧道 Verify 检查 OSPF 数据库 Troubleshoot 故障排除命令 Related Information Introduction 开放最短路径优先 (OSPF) 自治系统中的所有区域都必须以物理方式与主干区域 ( 区域 0) 相连在无法实现这种连接的情况下, 可利用虚拟链路来通过非主干区域连接到主干网您还可利用虚拟链路来通过非主干区域连接一个主干网中分割而成的两个部分配置虚拟链路所使用的区域称为中转区域, 这种区域必须具有全部路由信息中转区域不能是末节区域本文档对虚拟链路环境中的 OSPF 数据库进行了说明有关虚拟链路的详细信息, 请参阅 OSPF 设计指南 Prerequisites Requirements Cisco 建议您了解以下主题 : 配置 OSPF OSPF 区域间路由 Components Used 本文档不限于特定的软件或硬件版本

The information in this document was created from the devices in a specific lab environment.all of the devices used in this document started with a cleared (default) configuration.

2 The information in this document was created from the devices in a specific lab environment.all of the devices used in this document started with a cleared (default) configuration.if your network is live, make sure that you understand the potential impact of any command. Conventions Refer to Cisco Technical Tips Conventions for more information on document conventions. Configure 本部分提供有关如何配置本文档所述功能的信息 Note: 有关本文档所用命令的详细信息, 请使用命令查找工具 ( 仅限注册用户 ) Network Diagram 本文档使用以下网络设置 : 配置本文档使用以下配置 : Router Router Router Router Current configuration: hostname Router interface Loopback0

3 ip address interface Ethernet2/0/0 ip address interface Serial2/1/0 ip address router ospf 2 network area 0 network area 1 area 1 virtual-link !--- Area 1 is the transit area.!--- IP address is the router!--- ID of the router between Area 1!--- and Area 2 (Router ). See!--- the next Note. end Note: 如果一个存在, OSPF 路由器 ID 通常是在机箱或最较高的环回地址的最高的 IP 地址路由器 ID 只被计算在启动时间或在任何时间 OSPF 进程被重新启动发出 show ip ospf interface 命令查找路由器 ID Router Current configuration: hostname Router interface Loopback0 ip address interface Serial0/1/0 ip address interface ATM1/0.20 point-to-point ip address router ospf 2 network area 1 network area 1 end Router Current configuration: hostname Router interface Loopback0 ip address interface Ethernet0/0 ip address interface ATM2/0.20 point-to-point ip address router ospf 2 network area 2 network area 1 area 1 virtual-link !--- Area 1 is the transit area.!--- IP address is the router!--- ID of the router between Area 1!---

4 and Area 0 (Router ). end 虚链路如何运行最初, 虚链路发生故障, 因为 Router 不会到达 Router ( 虚链路的另一个末端 ) 所有在第 1 区需要的 Link State Advertisement (LSA) 被充斥和 Shortest Path First (SPF) 算法必须在第 1 区内由所有三路由器负责, Router 的能会通过第 1. 区到达 Router 在路由器会通过中转区域后互相到达, 他们设法形成在虚链路间的邻接在虚链路之间的二末端的 OSPF 信息包不是组播信息包因为他们被建立隧道对虚链路的另一个末端, 他们是自来源的隧道信息包对目的地请注意, 如果有在虚拟链路路由器之间的一防火墙, 您需要 enable (event) 在和之间的虚拟链路隧道流出的接口 IP 之间的 OSPF (IP 协议 89) 端口一旦路由器变得相邻在虚链路, Router 认为自己区域边界路由器 (ABR), 因为结果当前有一条链路在 Area 0, Router 创建 /8 的一个汇总 LSA 在 Area 0 和在第 1. 区由于某种原因如果虚链路是不正确的配置的, 则 Router 不认为自己 ABR, 因为没有在 Area 0 的任何接口如果这是实际情形, 不创建汇总 LSA 也不通告 /8 到第 1. 区 Note: OSPF 运行在它上面 IP 并且使用协议号 89 OSPF 不依靠任何其他传输协议, 例如 TCP 和 UDP 计算最短路径此部分从 Router 的角度计算最短路径 Router 在其自己的 LSA 查找并且看到 Router 是相邻它然后查看 Router LSA 验证 Router 看到 Router 作为相邻如果两路由器互相看到作为相邻, 则他们认为可达到每个路由器也检查您能用 show ip ospf neighbor 命令看到 ) 的其本地邻接表 ( 验证其接口和相邻的接口在一个普通的 IP 子网 Note: 此检查在未编号的接口没有被执行如果他们在一个普通的子网, 所有末端网络的路由器安装路由在他们的相邻路由器 LSA 列出了在本例中, /8 是在 Router LSA 列出的唯一的 stub 网络在第 1 区, Router 已经直接地被连接 Router 执行 Router LSA 的同一个考试, 但是没有在 Router LSA 的所有有用的末端网络在所有可达路由器 LSA 在第 1 区被检查后, Router 查看在数据库的汇总 LSA 它查找 /8 的两个汇总 LSA 在第 1 区并且选择那个以最低的总费用, 是到达通告路由器的权值加上汇总 LSA 的权值 Router 能通过 Router 到达以一费用的 = 139 Router 能通过 Router 到达以一费用的 = 11 Router 在其路由表里安装一个路由通过与权值的 Router 此输出在以前被描述的每个路由器里路由表显示 OSPF 路由 :

5 Router #show ip route ospf!--- Output suppressed. O /8 [110/65] via , 00:38:12, Serial2/1/0 O IA /8 [110/75] via , 00:38:02, Serial2/1/0 Router #show ip route ospf!--- Output suppressed. O IA /8 [110/74] via , 00:38:08, Serial0/1/0 O IA /8 [110/11] via , 00:38:12, ATM1/0.20!--- This is the route in this example. Router #show ip route ospf!--- Output suppressed. O /8 [110/75] via , 00:38:18, ATM2/0.20 O /8 [110/65] via , 00:38:28, ATM2/0.20 使用而不是虚链路的 GRE 封装隧道您在 Area 0 能也构建在 Router 和 Router 之间的一条通用路由封装 (GRE) 隧道和放置隧道 GRE 封装隧道和虚链路之间的主要区别在此表描述 : GRE 封装隧道在隧道的所有数据流由隧道终点封装并且解封装在顶上每个信息包的原因的隧道报头隧道可以通过末端区域虚拟链路路由更新被建立隧道, 但是本地发送数据流量数据流量不是受顶上任何的隧道支配因为路由器在末端区域没有外部目的地的, 路由中转区域不可以是末端区域由于本地发送数据, 如果为一个外部目的地注定的信息包被发送到也是中转区域的末端区域, 然后信息包没有正确地路由路由器在末端区域没有特定外部目的地的路由 Verify Use this section to confirm that your configuration works properly. 命令输出解释程序 ( 仅限注册用户 )(OIT) 支持某些 show 命令使用 OIT 可查看对 show 命令输出的分析 show ip ospf database 显示 LSA 列表并且键入他们到一个链路状态数据库此列表在 LSA 报头显示仅信息显示所有列表一个路由器的 LSA 在数据库的 LSA 是由每个路由器生产的这些根本 LSA 与状态和链路流出开销一起列出所有路由器或接口的链路, 并且他们在他们产生的区域内仅被充斥显示仅信息关于在数据库的网络汇总 LSA

6 show ip ospf database [summary] [self-originate] 显示仅自已生成的 LSA ( 从本地路由器 ) 检查 OSPF 数据库这是 OSPF 数据库如何看起来给出此网络环境, 当您发出 show ip ospf database 命令时 Router #show ip ospf database OSPF Router with ID ( ) (Process ID 2) Router Link States (Area 0) Link ID ADV Router Age Seq# Checksum Link count x xD5DF (DNA) 0x x Summary Net Link States (Area 0) Link ID ADV Router Age Seq# Checksum x xAA (DNA) 0x x7A x xA (DNA) 0x xEA3F (DNA) 0x xF624 Router Link States (Area 1) Link ID ADV Router Age Seq# Checksum Link count x xDDA x x64DD x xA14C 2 Summary Net Link States (Area 1) Link ID ADV Router Age Seq# Checksum x x x xEBF x xBF x xF624 Router #show ip ospf database OSPF Router with ID ( ) (Process ID 2) Router Link States (Area 1) Link ID ADV Router Age Seq# Checksum Link count x xDDA x x64DD x xA14C 2 Summary Net Link States (Area 1) Link ID ADV Router Age Seq# Checksum x x x xEBF x xBF x xF624 Router #show ip ospf database

7 OSPF Router with ID ( ) (Process ID 2) Router Link States (Area 0) Link ID ADV Router Age Seq# Checksum Link count (DNA) 0x xD5DF x x Summary Net Link States (Area 0) Link ID ADV Router Age Seq# Checksum (DNA) 0x xAA x x7A (DNA) 0x xA x xEA3F x xF624 Router Link States (Area 1) Link ID ADV Router Age Seq# Checksum Link count x xDDA x x64DD x xA14C 2 Summary Net Link States (Area 1) Link ID ADV Router Age Seq# Checksum x x x xEBF x xBF x xF624 Router Link States (Area 2) Link ID ADV Router Age Seq# Checksum Link count x xCF5 1 Summary Net Link States (Area 2) Link ID ADV Router Age Seq# Checksum x xEBF x x7A x xEA3F 注意通过虚链路了解的 LSA 有 DoNotAge 选项虚链路对待类似需求电路 Router #show ip ospf database router OSPF Router with ID ( ) (Process ID 2) Router Link States (Area 0) LS age: 1100 LS Type: Router Links Link State ID: !--- For router links, Link State ID is always the same as the Advertising Router. Advertising Router: !--- This is the router ID of the router that created this LSA. LS Seq Number: Checksum: 0xD5DF Length: 48 Area Border Router!--- Bit B in the router LSA indicates that this router is an ABR. Number of Links: 2!--- There are two links in Area 0. Link connected to: a Virtual Link (Link ID) Neighboring Router ID:

8 !--- Router ID of the neighbor on the other end of the virtual link. (Link Data) Router Interface address: !--- The interface that this router uses to send packets to the neighbor. Number of TOS metrics: 0 TOS 0 Metrics: 65!--- The metric comes from the cost for this router to reach the neighboring router:!--- the ATM link has a cost of 1 and the serial link has a cost of 64. Link connected to: a Stub Network!--- This represents the Ethernet segment /8. (Link ID) Network/subnet number: (Link Data) Network Mask: Number of TOS metrics: 0 TOS 0 Metrics: 10 Router Link States (Area 1) LS age: 122 LS Type: Router Links Link State ID: Advertising Router: LS Seq Number: Checksum: 0xDBA7 Length: 48 Area Border Router Number of Links: 2!--- There are two links in Area 1. Link connected to: another Router (point-to-point) (Link ID) Neighboring Router ID: (Link Data) Router Interface address: Number of TOS metrics: 0 TOS 0 Metrics: 64 Link connected to: a Stub Network (Link ID) Network/subnet number: (Link Data) Network Mask: Number of TOS metrics: 0 TOS 0 Metrics: 64 Router #show ip ospf database router OSPF Router with ID ( ) (Process ID 2) Router Link States (Area 1) LS age: 245 LS Type: Router Links Link State ID: Advertising Router: LS Seq Number: Checksum: 0x64DD Length: 72 Number of Links: 4!--- There are four links in Area 1. Link connected to: another Router (point-to-point) (Link ID) Neighboring Router ID: (Link Data) Router Interface address: Number of TOS metrics: 0 TOS 0 Metrics: 1 Link connected to: a Stub Network (Link ID) Network/subnet number: (Link Data) Network Mask: Number of TOS metrics: 0 TOS 0 Metrics: 1 Link connected to: another Router (point-to-point) (Link ID) Neighboring Router ID: (Link Data) Router Interface address: Number of TOS metrics: 0 TOS 0 Metrics: 64 Link connected to: a Stub Network (Link ID) Network/subnet number: (Link Data) Network Mask: Number of TOS metrics: 0 TOS 0 Metrics: 64 Router #show ip ospf database router OSPF Router with ID ( ) (Process ID 2) Router Link States (Area 0) Routing Bit Set on this LSA LS age: 5 (DoNotAge) LS Type: Router Links Link State ID: Checksum: 0x3990 Length: 36 Area Border Router Number of Links: 1!--- There is one link in Area 0. Link connected to: a Virtual Link (Link ID) Neighboring Router ID: (Link Data) Router Interface address: Number of TOS metrics: 0 TOS 0 Metrics: 65 Routing Bit Set on this LSA LS age: 1137 Router Link States (Area 1)

9 LS Type: Router Links Link State ID: LS Seq Number: Checksum: 0xA14C Length: 48 Area Border Router Number of Links: 2!--- There are two links in Area 1. Link connected to: another Router (point-to-point) (Link ID) Neighboring Router ID: (Link Data) Router Interface address: Number of TOS metrics: 0 TOS 0 Metrics: 1 Link connected to: a Stub Network (Link ID) Network/subnet number: (Link Data) Network Mask: Number of TOS metrics: 0 TOS 0 Metrics: 1 Router 认为自己 ABR, 因为有 Area 0 ( 虚链路 ) 的一条链路结果, 它生成的一个汇总 LSA 到第 1 区和 Area 0, 您能看到, 当您发出 show ip ospf database summary 命令时 Router #show ip ospf database summary OSPF Router with ID ( ) (Process ID 2) Summary Net Link States (Area 0) LS age: 1779 Link State ID: (summary Network Number) LS Seq Number: Checksum: 0xF624 TOS: 0 Metric: 10 Summary Net Link States (Area 1) LS age: 1766 Link State ID: (summary Network Number) Advertising Router: LS Seq Number: Checksum: 0xBF22 TOS: 0 Metric: 75 LS age: 1781 Link State ID: (summary Network Number) LS Seq Number: Checksum: 0xF624 TOS: 0 Metric: 10 并且, 请注意 Router 在第 2 区创建汇总 LSA 从 Area 0 和区域 1. 了解的所有的信息 Router #show ip ospf database summary self-originate

10 OSPF Router with ID ( ) (Process ID 2) Summary Net Link States (Area 0) LS age: 155 Link State ID: (summary Network Number) Checksum: 0x7871 TOS: 0 Metric: 65 LS age: 155 Link State ID: (summary Network Number) Checksum: 0xE840 TOS: 0 Metric: 1 LS age: 156 Link State ID: (summary Network Number) Checksum: 0xF425 TOS: 0 Metric: 10 Summary Net Link States (Area 1) LS age: 157 Link State ID: (summary Network Number) Checksum: 0xE9F6 TOS: 0 Metric: 75 LS age: 165 Link State ID: (summary Network Number) Checksum: 0xF425 TOS: 0 Metric: 10 LS age: 167 Summary Net Link States (Area 2)

11 Link State ID: (summary Network Number) Checksum: 0xE9F6 TOS: 0 Metric: 75 LS age: 168 Link State ID: (summary Network Number) Checksum: 0x7871 TOS: 0 Metric: 65 LS age: 168 Link State ID: (summary Network Number) Checksum: 0xE840 TOS: 0 Metric: 1 Troubleshoot 使用本部分可排除配置故障故障排除命令命令输出解释程序 ( 仅限注册用户 )(OIT) 支持某些 show 命令使用 OIT 可查看对 show 命令输出的分析 Note: 使用 debug 命令之前, 请参阅有关 Debug 命令的重要信息 debug ip ospf adj 显示介入的事件构建或中断 OSPF 邻接路由器变得相邻并且通过虚链路交换 LSA, 类似于一条物理链路如果检查路由器 LSA 或输出的 debug ip ospf adj 命令, 您能看到邻接 : Router # May 26 17:25:03.089: OSPF: Rcv hello from area 0 from OSPF_VL May 26 17:25:03.091: OSPF: 2 Way Communication to on OSPF_VL3, state 2WAY May 26 17:25:03.091: OSPF: Send DBD to on OSPF_VL3 seq 0xD1C opt 0x62 flag 0x7 len 32 May 26 17:25:03.135: OSPF: End of hello processing May 26 17:25:03.139: OSPF: Rcv DBD from on OSPF_VL3 seq 0x1617 opt 0x22 flag 0x7 len 32 mtu 0 state EXSTART May 26 17:25:03.175: OSPF: First DBD and we are not SLAVE May 26 17:25:03.179: OSPF: Rcv DBD from on OSPF_VL3

12 seq 0xD1C opt 0x22 flag 0x2 len 172 mtu 0 state EXSTART May 26 17:25:03.183: OSPF: NBR Negotiation Done. We are the MASTER May 26 17:25:03.189: OSPF: Send DBD to on OSPF_VL3 seq 0xD1D opt 0x62 flag 0x3 len 172 May 26 17:25:03.191: OSPF: Database request to May 26 17:25:03.191: OSPF: sent LS REQ packet to , length 36 May 26 17:25:03.263: OSPF: Rcv DBD from on OSPF_VL3 seq 0xD1D opt 0x22 flag 0x0 len 32 mtu 0 state EXCHANGE May 26 17:25:03.267: OSPF: Send DBD to on OSPF_VL3 seq 0xD1E opt 0x62 flag 0x1 len 32 May 26 17:25:03.311: OSPF: Rcv DBD from on OSPF_VL3 seq 0xD1E opt 0x22 flag 0x0 len 32 mtu 0 state EXCHANGE May 26 17:25:03.311: OSPF: Exchange Done with on OSPF_VL3 May 26 17:25:03.315: OSPF: Synchronized with on OSPF_VL3, state FULL May 26 17:25:03.823: OSPF: Build router LSA for area 0, router ID , seq 0x May 26 17:25:03.854: OSPF: Dead event ignored for on demand circuit OSPF_VL3 Router #show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface FULL/ - 00:00: ATM2/0.20 Router #show ip ospf virtual-links Virtual Link OSPF_VL3 to router is up Run as demand circuit DoNotAge LSA allowed. Transit area 1, via interface ATM2/0.20, Cost of using 65 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:01 Adjacency State FULL (Hello suppressed) Index 1/2, retransmission queue length 0, number of retransmission 0 First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0) Last retransmission scan length is 0, maximum is 0 Last retransmission scan time is 0 msec, maximum is 0 msec 注意在虚链路的邻接在 show ip ospf neighbor 命令输出中没有显示看到他们的唯一方法是查看路由器 LSA 和观察调试指令, 因为邻接出来, 或者发出 show ip ospf virtual-links 命令 Related Information 什么是 OSPF 区域和虚链路? 在虚拟链路上配置 OSPF 认证配置在 IPSec 的一个 GRE 封装隧道使用 OSPF 什么 show ip ospf interface 命令显示? OSPF 如何传播外部路由到多个区域 OSPF 数据库说明指南 OSPF 支持页 IP 路由协议支持页 IP 路由支持页 Technical Support & Documentation - Cisco Systems

基于点到点链路的 OSPF 的初始配置

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