3.3 OSPF特性

2.虚电路Virtual Link

如果非骨干区域与骨干区域没有相连，可以使用虚电路Virtual Link临时解决。
[R1]ospf 1 router-id 1.1.1.1
R1-ospf-1]area 0
[R1-ospf-1-area-0.0.0.0]network 12.1.1. 0.255.255.255
[R1-ospf-1-area-0.0.0.0]network 1.1.1.1 0.0.0.0

[R2]ospf 1 router-id 2.2.2.2
[R2-ospf-1]area 0
[R2-ospf-1-area-0.0.0.0]network 2.2.2.2 0.0.0.0
[R2-ospf-1-area-0.0.0.0]network 12.1.1. 0.255.255.255

[R2-ospf-1]area 1
[R2-ospf-1-area-0.0.0.0]network 23.1.1. 0.255.255.255
[R2-ospf-1-area-0.0.0.1]vlink-peer 3.3.3.3

[R3]ospf 1 router-id 3.3.3.3
[R3-ospf-1]area 1
[R3-ospf-1-area-0.0.0.1]network 3.3.3.3 0.0.0.0
[R3-ospf-1-area-0.0.0.0]network 23.1.1. 0.255.255.255
[R3-ospf-1-area-0.0.0.1]vlink-peer 2.2.2.2
[R3-ospf-1]area 2
[R3-ospf-1-area-0.0.0.2]network 34.1.1. 0.255.255.255

[R4]ospf 1 router-id 4.4.4.4
[R4-ospf-1]area 2
[R4-ospf-1-area-0.0.0.2]network 4.4.4.4 0.0.0.0
[R4-ospf-1-area-0.0.0.2]network 34.1.1. 0.255.255.255
<R4>display ip routing-table 
Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface
1.1.1.1/32  OSPF    10   3           D   34.1.1.3        GigabitEthernet0/0/0
2.2.2.2/32  OSPF    10   2           D   34.1.1.3        GigabitEthernet0/0/0
3.3.3.3/32  OSPF    10   1           D   34.1.1.3        GigabitEthernet0/0/0
12.0.0.0/8   OSPF    10   3           D   34.1.1.3        GigabitEthernet0/0/0
23.0.0.0/8   OSPF    10   2           D   34.1.1.3        GigabitEthernet0/0/0
34.0.0.0/8   Direct  0    0           D   34.1.1.4        GigabitEthernet0/0/0

3.默认路由

1）在常规区域发布默认路由

[R1]ospf 1 router-id 1.1.1.1
[R1-ospf-1-area-0.0.0.0]network 1.1.1.1 0.0.0.0
[R1-ospf-1-area-0.0.0.0]network 12.1.1.0 0.255.255.255
[R1-ospf-1-area-0.0.0.0]network 13.1.1.0 0.255.255.255

[R2]ospf 1 router-id 2.2.2.2
[R2-ospf-1]area 0
[R2-ospf-1-area-0.0.0.0]network 12.1.1.0 0.255.255.255
[R2-ospf-1]area 1
[R2-ospf-1-area-0.0.0.1]network 2.2.2.2 0.0.0.0
[R3]ospf 1 router-id 3.3.3.3
[R3-ospf-1]area 0
[[R3-ospf-1-area-0.0.0.0]network 13.1.1.0 0.255.255.255
[R3-ospf-1]area 2
[R3-ospf-1-area-0.0.0.2]network 3.3.3.3 0.0.0.0

[R1]ip route-static 0.0.0.0 0.0.0.0 14.1.1.4
[R4]ip route-static 0.0.0.0 0.0.0.0 14.1.1.1
静态和其他动态默认路由不会被引入OSPF，使用以下命令发布一天默认路由，默认采用Type-5LSA来描述，如果增加always关键字，无论是否已经定义默认路由，都始终下发默认路由。
[R1-ospf-1]default-route-advertise cost 10 type  2
[R1-ospf-1]display ip routing-table
Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface
0.0.0.0/0   Static  60   0          RD   14.1.1.4        GigabitEthernet0/0/2

2）在Stub区域发布默认路由

通俗的理解Stub区域，就是削减了四类、五类LSA。区域内包含：Type-1、Type-2、Type-3和一条缺省Type-3LSA。
[R2-ospf-1-area-0.0.0.1]stub
[R5]ospf 1 router-id 5.5.5.5
[R5-ospf-1]area 1
[R5-ospf-1-area-0.0.0.1]network 5.5.5.5 0.0.0.0
[R5-ospf-1-area-0.0.0.1]network 25.1.1.0 0.255.255.255
[R5-ospf-1-area-0.0.0.1]stub 
[R5-ospf-1]display ospf lsdb
         OSPF Process 1 with Router ID 5.5.5.5
                 Link State Database 
                         Area: 0.0.0.1
 Type      LinkState ID    AdvRouter          Age  Len   Sequence   Metric
 Router    2.2.2.2         2.2.2.2            131  48    80000006       0
 Router    5.5.5.5         5.5.5.5            126  48    80000006       0
 Network   25.1.1.5        5.5.5.5            126  32    80000002       0
 Sum-Net   0.0.0.0         2.2.2.2            178  28    80000001       1
 Sum-Net   3.3.3.3         2.2.2.2            178  28    80000001       2
 Sum-Net   13.0.0.0        2.2.2.2            178  28    80000001       2
 Sum-Net   1.1.1.1         2.2.2.2            178  28    80000001       1
 Sum-Net   12.0.0.0        2.2.2.2            178  28    80000001       1
[R5-ospf-1]dis ip routing-table
Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface
0.0.0.0/0   OSPF    10   2           D   25.1.1.2        GigabitEthernet0/0/1

3）在 Totally Stub区域发布默认路由

通过配置Totally Stub区域，进一步缩减三类LSA的条目。区域内包含：Type-1、Type-2和一条缺省Type-3LSA。
[R2-ospf-1-area-0.0.0.1]stub no-summary 
[R5-ospf-1-area-0.0.0.1]stub no-summary
[R5-ospf-1-area-0.0.0.1]display ospf lsdb
                         Area: 0.0.0.1
 Type      LinkState ID    AdvRouter          Age  Len   Sequence   Metric
 Router    2.2.2.2         2.2.2.2            111  48    8000000C       0
 Router    5.5.5.5         5.5.5.5            105  48    8000000C       0
 Network   25.1.1.5        5.5.5.5            105  32    80000002       0
 Sum-Net   0.0.0.0         2.2.2.2            750  28    80000001       1

[R5-ospf-1-area-0.0.0.1]dis ospf routing
         OSPF Process 1 with Router ID 5.5.5.5
                  Routing Tables 
 Routing for Network 
Destination        Cost  Type       NextHop         AdvRouter       Area
5.5.5.5/32         0     Stub       5.5.5.5         5.5.5.5         0.0.0.1
25.0.0.0/8         1     Transit    25.1.1.5        5.5.5.5         0.0.0.1
0.0.0.0/0          2     Inter-area 25.1.1.2        2.2.2.2         0.0.0.1
2.2.2.2/32         1     Stub       25.1.1.2        2.2.2.2         0.0.0.1

4）在 NSSA区域发布默认路由

只包含一类、二类、三类LSA，以及七类LSA
[R3-ospf-1-area-0.0.0.2]network 36.1.1.0 0.255.255.255
[R3-ospf-1-area-0.0.0.2]nssa
[R6]ospf 1 router-id 6.6.6.6
[R6-ospf-1]area 2
[R6-ospf-1-area-0.0.0.2]network 36.1.1.0 0.255.255.255
[R6-ospf-1-area-0.0.0.2]nssa 
[R6-ospf-1]import-route rip 
[R6]rip 1
[R6-rip-1]version 2
[R6-rip-1]network 6.0.0.0             
[R6-rip-1]network 192.168.6.0
[R6-rip-1]import-route ospf

[R6-ospf-1-area-0.0.0.2]display ospf lsdb 
         OSPF Process 1 with Router ID 6.6.6.6
                 Link State Database 
                         Area: 0.0.0.2
 Type      LinkState ID    AdvRouter          Age  Len   Sequence   Metric
 Router    6.6.6.6         6.6.6.6              2  36    80000028       1
 Router    3.3.3.3         3.3.3.3             10  48    8000002C       0
 Network   36.1.1.6        6.6.6.6              4  32    80000002       0
 Sum-Net   5.5.5.5         3.3.3.3             14  28    80000001       3
 Sum-Net   25.0.0.0        3.3.3.3             14  28    80000001       3
 Sum-Net   2.2.2.2         3.3.3.3             14  28    80000001       2
 Sum-Net   13.0.0.0        3.3.3.3             14  28    80000001       1
 Sum-Net   1.1.1.1         3.3.3.3             14  28    80000001       1
 Sum-Net   12.0.0.0        3.3.3.3             14  28    80000001       2
 NSSA      192.168.6.0     6.6.6.6             22  36    80000001       1
 NSSA      6.6.6.6         6.6.6.6             22  36    80000001       1
 NSSA      0.0.0.0         3.3.3.3             12  36    80000004       1


[R6-ospf-1-area-0.0.0.2]display  ip routing-table
 0.0.0.0/0   O_NSSA  150  1           D   36.1.1.3        GigabitEthernet0/0/0
 1.1.1.1/32  OSPF    10   2           D   36.1.1.3        GigabitEthernet0/0/0
        2.2.2.2/32  OSPF    10   3           D   36.1.1.3        GigabitEthernet0/0/0
        3.3.3.3/32  OSPF    10   1           D   36.1.1.3        GigabitEthernet0/0/0
        5.5.5.5/32  OSPF    10   4           D   36.1.1.3        GigabitEthernet0/0/0
            12.0.0.0/8   OSPF    10   3           D   36.1.1.3        GigabitEthernet0/0/0
       13.0.0.0/8   OSPF    10   2           D   36.1.1.3        GigabitEthernet0/0/0
       25.0.0.0/8   OSPF    10   4           D   36.1.1.3        GigabitEthernet0/0/0

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