观察OSPF虚链路和虚链路的替代办法

 Mar 16th 23  PNETLab 7 minutes read (About 977 words)
This is an article that was created 552 days ago, and the information may have evolved or changed.

一个小实验，观察OSPF虚链路、虚链路的替代办法。

拓扑图：

ScreenCaputure230316225301

如上图所示，右边 AREA 2、3、4 普通区域被 AREA 1 分割。

要求：不改动物理连线的方式配置设备，使得 R1 学习到 R6、R7、R8上的路由。

方式一：R2 – R3 间配置跨 AREA 1 的虚链路

方式二：R2 – R4 间配置 Tunnel 隧道，配置宣告

方式三：R5 上 配置 AREA 4 在另一个 OSPF 进程，配置重分布

方式一

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!--- R2 commands.

router ospf 100
 area 1 virtual-link 3.3.3.3
 
!--- R3 commands.

router ospf 100
 area 1 virtual-link 2.2.2.2

方式二

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!--- R2 commands.

!
interface Tunnel0
 ip address 100.1.1.1 255.255.255.252
 tunnel source 24.1.1.2
 tunnel destination 24.1.1.4
!
router ospf 100
 # 将Tunnel接口地址宣告进区域0
 network 100.1.1.1 0.0.0.0 area 0
!
 
!--- R4 commands.

interface Tunnel0
 ip address 100.1.1.2 255.255.255.252
 tunnel source 24.1.1.4
 tunnel destination 24.1.1.2
!
router ospf 100
 # 将Tunnel接口地址宣告进区域0
 network 100.1.1.2 0.0.0.0 area 0
!

方式三

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R5#sh run | s r o
router ospf 100
 router-id 5.5.5.5
 # 重分布
 redistribute ospf 200 subnets
 network 5.5.5.5 0.0.0.0 area 1
 network 25.1.1.5 0.0.0.0 area 1
 
# 配置 AREA  4 在另一个 OSPF 进程
router ospf 200
 router-id 55.55.55.55
 # 重分布
 redistribute ospf 100 subnets
 network 58.1.1.5 0.0.0.0 area 4
R5#

观察

R1 上查看 OSPF 路由，发现能学习到 R6，R7，R8上的环回口路由；Tunnel接口的地址也被学习到，而且是 O 表项路由属于区域 0 ，R8 的路由因为在R5 上进行了双向重分布显示为 OE2 表项。 R6，R7 则是区域间路由，逻辑上的直连区域0。

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R1#sh ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      2.0.0.0/32 is subnetted, 1 subnets
O        2.2.2.2 [110/11] via 12.1.1.2, 00:26:14, Ethernet0/0
      3.0.0.0/32 is subnetted, 1 subnets
O IA     3.3.3.3 [110/21] via 12.1.1.2, 00:25:54, Ethernet0/0
      4.0.0.0/32 is subnetted, 1 subnets
O IA     4.4.4.4 [110/21] via 12.1.1.2, 00:26:03, Ethernet0/0
      5.0.0.0/32 is subnetted, 1 subnets
O IA     5.5.5.5 [110/21] via 12.1.1.2, 00:26:03, Ethernet0/0
      6.0.0.0/32 is subnetted, 1 subnets
O IA     6.6.6.6 [110/31] via 12.1.1.2, 00:25:54, Ethernet0/0
      7.0.0.0/32 is subnetted, 1 subnets
O IA     7.7.7.7 [110/1021] via 12.1.1.2, 00:25:53, Ethernet0/0
      8.0.0.0/32 is subnetted, 1 subnets
O E2     8.8.8.8 [110/11] via 12.1.1.2, 00:25:53, Ethernet0/0
      23.0.0.0/24 is subnetted, 1 subnets
O IA     23.1.1.0 [110/20] via 12.1.1.2, 00:26:14, Ethernet0/0
      24.0.0.0/24 is subnetted, 1 subnets
O IA     24.1.1.0 [110/20] via 12.1.1.2, 00:26:14, Ethernet0/0
      25.0.0.0/24 is subnetted, 1 subnets
O IA     25.1.1.0 [110/20] via 12.1.1.2, 00:26:14, Ethernet0/0
      36.0.0.0/24 is subnetted, 1 subnets
O IA     36.1.1.0 [110/30] via 12.1.1.2, 00:25:54, Ethernet0/0
      47.0.0.0/24 is subnetted, 1 subnets
O IA     47.1.1.0 [110/1020] via 12.1.1.2, 00:26:14, Ethernet0/0
      58.0.0.0/24 is subnetted, 1 subnets
O E2     58.1.1.0 [110/10] via 12.1.1.2, 00:25:54, Ethernet0/0
      100.0.0.0/30 is subnetted, 1 subnets
O        100.1.1.0 [110/1010] via 12.1.1.2, 00:26:14, Ethernet0/0
R1#

R2上查看 OSPF 邻居，发现除常规的邻居外，还有Tunnel0 的邻居和虚链路的邻居，两种邻居的区别在于虚链路邻居一旦邻居建立处于稳定状态，不发送hello报文，而且Dead Time 永不超时。而Tunnel0 的邻居有Dead Time 默认40秒，debug 查看 hello 会发现*Mar 16 15:24:11.782: OSPF-100 HELLO Tu0: Rcv hello from 4.4.4.4 area 0 100.1.1.2，好像没什么用，好看

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R2#sh ip os nei

Neighbor ID     Pri   State           Dead Time   Address         Interface
4.4.4.4           0   FULL/  -        00:00:30    100.1.1.2       Tunnel0
1.1.1.1           1   FULL/BDR        00:00:32    12.1.1.1        Ethernet0/0
3.3.3.3           0   FULL/  -           -        23.1.1.3        OSPF_VL0
5.5.5.5           1   FULL/DR         00:00:33    25.1.1.5        Ethernet0/3
4.4.4.4           1   FULL/DR         00:00:34    24.1.1.4        Ethernet0/2
3.3.3.3           1   FULL/DR         00:00:37    23.1.1.3        Ethernet0/1
R2#

R8上查看路由表，因为在R5上进行了重分布，R5是ASBR。所有看到的OSPF路由表项都是 OE

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R8#sh ip rou os
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      1.0.0.0/32 is subnetted, 1 subnets
O E2     1.1.1.1 [110/21] via 58.1.1.5, 00:41:42, Ethernet0/0
      2.0.0.0/32 is subnetted, 1 subnets
O E2     2.2.2.2 [110/11] via 58.1.1.5, 00:41:42, Ethernet0/0
      3.0.0.0/32 is subnetted, 1 subnets
O E2     3.3.3.3 [110/21] via 58.1.1.5, 00:41:42, Ethernet0/0
      4.0.0.0/32 is subnetted, 1 subnets
O E2     4.4.4.4 [110/21] via 58.1.1.5, 00:41:42, Ethernet0/0
      5.0.0.0/32 is subnetted, 1 subnets
O E2     5.5.5.5 [110/1] via 58.1.1.5, 00:41:42, Ethernet0/0
      6.0.0.0/32 is subnetted, 1 subnets
O E2     6.6.6.6 [110/31] via 58.1.1.5, 00:41:41, Ethernet0/0
      7.0.0.0/32 is subnetted, 1 subnets
O E2     7.7.7.7 [110/31] via 58.1.1.5, 00:01:46, Ethernet0/0
      12.0.0.0/24 is subnetted, 1 subnets
O E2     12.1.1.0 [110/20] via 58.1.1.5, 00:41:42, Ethernet0/0
      23.0.0.0/24 is subnetted, 1 subnets
O E2     23.1.1.0 [110/20] via 58.1.1.5, 00:41:42, Ethernet0/0
      24.0.0.0/24 is subnetted, 1 subnets
O E2     24.1.1.0 [110/20] via 58.1.1.5, 00:41:42, Ethernet0/0
      25.0.0.0/24 is subnetted, 1 subnets
O E2     25.1.1.0 [110/10] via 58.1.1.5, 00:41:42, Ethernet0/0
      36.0.0.0/24 is subnetted, 1 subnets
O E2     36.1.1.0 [110/30] via 58.1.1.5, 00:41:42, Ethernet0/0
      47.0.0.0/24 is subnetted, 1 subnets
O E2     47.1.1.0 [110/30] via 58.1.1.5, 00:01:46, Ethernet0/0
      100.0.0.0/30 is subnetted, 1 subnets
O E2     100.1.1.0 [110/1010] via 58.1.1.5, 00:41:42, Ethernet0/0
R8#
R8# sh ip os border-routers 

            OSPF Router with ID (8.8.8.8) (Process ID 200)


                Base Topology (MTID 0)

Internal Router Routing Table
Codes: i - Intra-area route, I - Inter-area route

i 55.55.55.55 [10] via 58.1.1.5, Ethernet0/0, ASBR, Area 4, SPF 2
R8#
#Network Emulator #PNETLab #Cisco #OSPF #虚链路替代 #virtual-link
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