引言

我们在项目实施中可能会遇到以下问题，不规范的OSPF区域设计
1、area 0内出现单点故障使得OSPF拓扑出现两个area 0

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2、或者是另一种

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这该如何进行补救措施呢？

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我们在B、C路由器之间创建一条虚链路，这条虚链路是逻辑上的链接，默认只属于area 0

Vlink

1、只要创建Vlink的路由器都是ABR
2、Vlink永远属于区域0的链路
3、虚链路不能在区域0创建，只能在非骨干区域中创建，只能跨越一个非骨干区域，
4、特殊区域不能创建Vlink，特殊区域后边会阐述
5、用途：用于修复不连续的骨干区域，将非骨干区域和骨干区域直接相连
6、作为区域0的备用路径，能不用就别用
我们继续做以下实验模拟上述问题

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此时area 30里的路由不会通过R7进行泛洪，因此我们需要在R1和R7上进行Vlink的配置，如何配置呢？
R1

<R1>sys
Enter system view, return user view with Ctrl+Z.
[R1]ospf 1
[R1-ospf-1]a 20
[R1-ospf-1-area-0.0.0.20]vl 
[R1-ospf-1-area-0.0.0.20]vlink-peer 7.7.7.7#对端路由器的routerid

R7

<R7>sys
Enter system view, return user view with Ctrl+Z.
[R7]ospf 1
[R7-ospf-1]a 20
[R7-ospf-1-area-0.0.0.20]v  
  [R7-ospf-1-area-0.0.0.20]vlink-peer 1.1.1.1
Feb 17 2021 16:41:50-08:00 R7 %%01OSPF/4/VLINK_NBR_CHG_E(l)[22]:Virtual link pee
r event: neighbor status changed. (ProcessId=256,     VirtualLinkNeighborAddress=1.1
.1.1, NeighborEvent=HelloReceived, NeighborPreviousState=Down,     NeighborCurrentSt
ate=Init)

查看

  [R7]dis ospf vlink 
 OSPF Process 1 with Router ID 7.7.7.7
     Virtual Links 
 Virtual-link Neighbor-id  -> 1.1.1.1, Neighbor-State: Full
 Interface: 10.1.17.7 (GigabitEthernet0/0/0)
 Cost: 1  State: P-2-P  Type: Virtual 
 Transit Area: 0.0.0.20 
 Timers: Hello 10 , Dead 40 , Retransmit 5 , Transmit Delay 1 
 GR State: Normal

验证：
R8上路由信息前后对比

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我们在R5上进行到R8的路由计算
敲入一下命令查看，发现开销为52

<R5>dis ip routing-table protocol ospf 
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Public routing table : OSPF
     Destinations : 10       Routes : 10       

OSPF routing table status : <Active>
     Destinations : 10       Routes : 10
Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface

    1.1.1.1/32  OSPF    10   50          D   10.1.45.4       GigabitEthernet
0/0/0
      2.2.2.2/32  OSPF    10   2           D   10.1.45.4       GigabitEthernet
0/0/0
    3.3.3.3/32  OSPF    10   2           D   10.1.45.4       GigabitEthernet
0/0/0
    4.4.4.4/32  OSPF    10   1           D   10.1.45.4       GigabitEthernet
0/0/0
    7.7.7.7/32  OSPF    10   51          D   10.1.45.4       GigabitEthernet
0/0/0
    8.8.8.8/32  OSPF    10   52          D   10.1.45.4       GigabitEthernet
0/0/0
  10.1.12.0/24  OSPF    10   50          D   10.1.45.4       GigabitEthernet
0/0/0
  10.1.17.0/24  OSPF    10   51          D   10.1.45.4       GigabitEthernet
0/0/0
  10.1.78.0/24  OSPF    10   52          D   10.1.45.4       GigabitEthernet
0/0/0
 10.1.234.0/24  OSPF    10   2           D   10.1.45.4       GigabitEthernet
0/0/0
OSPF routing table status : <Inactive>
     Destinations : 0        Routes : 0
<R5>

接下来我们用5.5.5.5 ping 8.8.8.8，发现可ping同

<R5>ping -a 5.5.5.5 8.8.8.8
  PING 8.8.8.8: 56  data bytes, press CTRL_C to break
Reply from 8.8.8.8: bytes=56 Sequence=1 ttl=251 time=100 ms
Reply from 8.8.8.8: bytes=56 Sequence=2 ttl=251 time=90 ms
Reply from 8.8.8.8: bytes=56 Sequence=3 ttl=251 time=100 ms
Reply from 8.8.8.8: bytes=56 Sequence=4 ttl=251 time=70 ms
Reply from 8.8.8.8: bytes=56 Sequence=5 ttl=251 time=90 ms
  --- 8.8.8.8 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 70/90/100 ms
<R5>