ospf之nssa區域

首先作為nssa區域需要滿足以下條件：

2.該區域不能存在虛鏈路

3.和stub區域類似，該區域只有一個出口，只不過這個區域是ASBR

網絡拓撲

配置ospf，如拓撲，全網運行ospf，R1將環回口100-102重分佈直連進ospf100，R5將200-202環回口重分佈直連進ospf，根據最開始提到的條件，本拓撲的area1中[R1(ASBR),R2(ASBR]，area2中[R3(ABR),R4,R5(ASBR)]均滿足，那麼本節以area2中的R3-R4-R5為例，首先查看路由表：

R3#

102.0.0.0/24 is subnetted, 1 subnets

O E2 102.1.1.0 [110/20] via 23.1.1.1, 00:00:04, FastEthernet0/0

1.0.0.0/32 is subnetted, 1 subnets

O IA 1.1.1.1 [110/3] via 23.1.1.1, 00:00:04, FastEthernet0/0

2.0.0.0/32 is subnetted, 1 subnets

O IA 2.2.2.2 [110/2] via 23.1.1.1, 00:00:04, FastEthernet0/0

100.0.0.0/24 is subnetted, 1 subnets

O E2 100.1.1.0 [110/20] via 23.1.1.1, 00:00:04, FastEthernet0/0

101.0.0.0/24 is subnetted, 1 subnets

O E2 101.1.1.0 [110/20] via 23.1.1.1, 00:00:04, FastEthernet0/0

4.0.0.0/32 is subnetted, 1 subnets

O 4.4.4.4 [110/2] via 34.1.1.2, 00:00:04, FastEthernet1/0

O E2 201.1.1.0/24 [110/20] via 34.1.1.2, 00:00:04, FastEthernet1/0

5.0.0.0/32 is subnetted, 1 subnets

O 5.5.5.5 [110/3] via 34.1.1.2, 00:00:04, FastEthernet1/0

O E2 200.1.1.0/24 [110/20] via 34.1.1.2, 00:00:04, FastEthernet1/0

O E2 202.1.1.0/24 [110/20] via 34.1.1.2, 00:00:04, FastEthernet1/0

12.0.0.0/24 is subnetted, 1 subnets

O IA 12.1.1.0 [110/2] via 23.1.1.1, 00:00:06, FastEthernet0/0

45.0.0.0/24 is subnetted, 1 subnets

O 45.1.1.0 [110/2] via 34.1.1.2, 00:00:06, FastEthernet1/0

R4#

102.0.0.0/24 is subnetted, 1 subnets

O E2 102.1.1.0 [110/20] via 34.1.1.1, 00:01:30, FastEthernet0/0

1.0.0.0/32 is subnetted, 1 subnets

O IA 1.1.1.1 [110/4] via 34.1.1.1, 00:01:30, FastEthernet0/0

2.0.0.0/32 is subnetted, 1 subnets

O IA 2.2.2.2 [110/3] via 34.1.1.1, 00:01:30, FastEthernet0/0

100.0.0.0/24 is subnetted, 1 subnets

O E2 100.1.1.0 [110/20] via 34.1.1.1, 00:01:30, FastEthernet0/0

3.0.0.0/32 is subnetted, 1 subnets

O IA 3.3.3.3 [110/2] via 34.1.1.1, 00:01:30, FastEthernet0/0

101.0.0.0/24 is subnetted, 1 subnets

O E2 101.1.1.0 [110/20] via 34.1.1.1, 00:01:30, FastEthernet0/0

O E2 201.1.1.0/24 [110/20] via 45.1.1.2, 00:01:30, FastEthernet1/0

5.0.0.0/32 is subnetted, 1 subnets

O 5.5.5.5 [110/2] via 45.1.1.2, 00:01:30, FastEthernet1/0

O E2 200.1.1.0/24 [110/20] via 45.1.1.2, 00:01:30, FastEthernet1/0

23.0.0.0/24 is subnetted, 1 subnets

O IA 23.1.1.0 [110/2] via 34.1.1.1, 00:01:30, FastEthernet0/0

O E2 202.1.1.0/24 [110/20] via 45.1.1.2, 00:01:32, FastEthernet1/0

12.0.0.0/24 is subnetted, 1 subnets

O IA 12.1.1.0 [110/3] via 34.1.1.1, 00:01:32, FastEthernet0/0

R5#

34.0.0.0/24 is subnetted, 1 subnets

O 34.1.1.0 [110/2] via 45.1.1.1, 00:13:03, FastEthernet0/0

102.0.0.0/24 is subnetted, 1 subnets

1.0.0.0/32 is subnetted, 1 subnets

O IA 1.1.1.1 [110/5] via 45.1.1.1, 00:13:03, FastEthernet0/0

2.0.0.0/32 is subnetted, 1 subnets

O IA 2.2.2.2 [110/4] via 45.1.1.1, 00:13:03, FastEthernet0/0

100.0.0.0/24 is subnetted, 1 subnets

O E2 100.1.1.0 [110/20] via 45.1.1.1, 00:13:03, FastEthernet0/0

3.0.0.0/32 is subnetted, 1 subnets

O IA 3.3.3.3 [110/3] via 45.1.1.1, 00:13:03, FastEthernet0/0

101.0.0.0/24 is subnetted, 1 subnets

O E2 101.1.1.0 [110/20] via 45.1.1.1, 00:13:03, FastEthernet0/0

4.0.0.0/32 is subnetted, 1 subnets

O 4.4.4.4 [110/2] via 45.1.1.1, 00:13:03, FastEthernet0/0

23.0.0.0/24 is subnetted, 1 subnets

O IA 23.1.1.0 [110/3] via 45.1.1.1, 00:13:03, FastEthernet0/0

12.0.0.0/24 is subnetted, 1 subnets

O IA 12.1.1.0 [110/4] via 45.1.1.1, 00:13:04, FastEthernet0/0

其中R3從兩個方向收到了6條OE2的路由條目，R4也從兩個方向收到了6條OE2的路由條目，R5從一個方向收到了3條路由條目，接下來做一下nssa，如果要將該區域作為nssa區域，那麼在本區域內的每一臺設備都需要做nssa的配置，從ASBR（R5)一直做到ABR(R3):

R3#

router ospf 100

area 2 nssa default-information-originate

R4#

router ospf 100

area 2 nssa

R5#

router ospf 100

area 2 nssa

可以看到，這邊在該區域的ABR設備上敲的命令和其他設備上的不一樣，這個是為了保證路由可達，很多地方在講解ospf的nssa區域的時候都出現了類似的錯誤，如果只在R3（ABR）配置命令area 2 nssa 命令，會出現的情況是，當R1要去往R5上的環回口的時候，那麼會導致沒有回包路由的情況出現，所以為了能夠保證路由的可達性，需要R3在作為nssa區域的同時下方默認路由，查看R3-R5的路由表：

R3#

102.0.0.0/24 is subnetted, 1 subnets

O E2 102.1.1.0 [110/20] via 23.1.1.1, 00:07:24, FastEthernet0/0

1.0.0.0/32 is subnetted, 1 subnets

O IA 1.1.1.1 [110/3] via 23.1.1.1, 00:07:24, FastEthernet0/0

2.0.0.0/32 is subnetted, 1 subnets

O IA 2.2.2.2 [110/2] via 23.1.1.1, 00:07:24, FastEthernet0/0

100.0.0.0/24 is subnetted, 1 subnets

O E2 100.1.1.0 [110/20] via 23.1.1.1, 00:07:24, FastEthernet0/0

101.0.0.0/24 is subnetted, 1 subnets

O E2 101.1.1.0 [110/20] via 23.1.1.1, 00:07:24, FastEthernet0/0

4.0.0.0/32 is subnetted, 1 subnets

O 4.4.4.4 [110/2] via 34.1.1.2, 00:07:24, FastEthernet1/0

O N2 201.1.1.0/24 [110/20] via 34.1.1.2, 00:07:24, FastEthernet1/0

5.0.0.0/32 is subnetted, 1 subnets

O 5.5.5.5 [110/3] via 34.1.1.2, 00:07:24, FastEthernet1/0

O N2 200.1.1.0/24 [110/20] via 34.1.1.2, 00:07:24, FastEthernet1/0

O N2 202.1.1.0/24 [110/20] via 34.1.1.2, 00:07:24, FastEthernet1/0

12.0.0.0/24 is subnetted, 1 subnets

O IA 12.1.1.0 [110/2] via 23.1.1.1, 00:07:26, FastEthernet0/0

45.0.0.0/24 is subnetted, 1 subnets

O 45.1.1.0 [110/2] via 34.1.1.2, 00:07:26, FastEthernet1/0

R4#

1.0.0.0/32 is subnetted, 1 subnets

O IA 1.1.1.1 [110/4] via 34.1.1.1, 00:08:37, FastEthernet0/0

2.0.0.0/32 is subnetted, 1 subnets

O IA 2.2.2.2 [110/3] via 34.1.1.1, 00:08:37, FastEthernet0/0

3.0.0.0/32 is subnetted, 1 subnets

O IA 3.3.3.3 [110/2] via 34.1.1.1, 00:08:37, FastEthernet0/0

O N2 201.1.1.0/24 [110/20] via 45.1.1.2, 00:08:37, FastEthernet1/0

5.0.0.0/32 is subnetted, 1 subnets

O 5.5.5.5 [110/2] via 45.1.1.2, 00:08:37, FastEthernet1/0

O N2 200.1.1.0/24 [110/20] via 45.1.1.2, 00:08:37, FastEthernet1/0

23.0.0.0/24 is subnetted, 1 subnets

O IA 23.1.1.0 [110/2] via 34.1.1.1, 00:08:37, FastEthernet0/0

O N2 202.1.1.0/24 [110/20] via 45.1.1.2, 00:08:37, FastEthernet1/0

12.0.0.0/24 is subnetted, 1 subnets

O IA 12.1.1.0 [110/3] via 34.1.1.1, 00:08:37, FastEthernet0/0

O*N2 0.0.0.0/0 [110/1] via 34.1.1.1, 00:08:37, FastEthernet0/0

R5#

34.0.0.0/24 is subnetted, 1 subnets

O 34.1.1.0 [110/2] via 45.1.1.1, 00:09:21, FastEthernet0/0

1.0.0.0/32 is subnetted, 1 subnets

O IA 1.1.1.1 [110/5] via 45.1.1.1, 00:09:21, FastEthernet0/0

2.0.0.0/32 is subnetted, 1 subnets

O IA 2.2.2.2 [110/4] via 45.1.1.1, 00:09:21, FastEthernet0/0

3.0.0.0/32 is subnetted, 1 subnets

O IA 3.3.3.3 [110/3] via 45.1.1.1, 00:09:21, FastEthernet0/0

4.0.0.0/32 is subnetted, 1 subnets

O 4.4.4.4 [110/2] via 45.1.1.1, 00:09:21, FastEthernet0/0

23.0.0.0/24 is subnetted, 1 subnets

O IA 23.1.1.0 [110/3] via 45.1.1.1, 00:09:21, FastEthernet0/0

12.0.0.0/24 is subnetted, 1 subnets

O IA 12.1.1.0 [110/4] via 45.1.1.1, 00:09:21, FastEthernet0/0

O*N2 0.0.0.0/0 [110/1] via 45.1.1.1, 00:09:21, FastEthernet0/0

當將該區域area2作為nssa區域可以發現，在ABR（R3）設備上，將從ASBR傳過來的OE2（五類LSA）的條目轉換為了ON2（七類的LSA）的條目；在R4上，優化掉了從左邊的ABR傳過來的100-102的條目（5類的LSA），產生了一條由ABR下放的O*N2的默認路由指向ABR；R5在優化掉左邊ABR傳過來的路由條目（100-102）的同時也產生了一條由ABR下放的O*N2默認路由指向R4，當然，優化掉五類LSA的同時其實也優化掉了4類的LSA，因為5類的LSA由4類LSA通告的，也就是ASBR通告的，而4類的LSA就是指出誰是ASBR，既然沒有了5類LSA的存在，那麼4類LSA自然而然也就沒有了。

下面測試一下路由可達性:

R1#ping 200.1.1.1 source 100.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 200.1.1.1, timeout is 2 seconds:

Packet sent with a source address of 100.1.1.1

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 64/157/276 ms

沒有問題，現在R1上用源100.1.1.1 去ping 200.1.1.1 可以通信。

當然，nssa區域其實算不上最大化的ospf優化，要做到最大化的優化，還需要用到完全nssa區域（完全非完全末節區域），配置完全nssa，只需要基於nssa區域的基礎之上，在本區域的ABR上敲上area 2 nssa no-summary命令即可：

R3(config)#router ospf 100

R3(config-router)#no area 2 nssa defa

R3(config-router)#no area 2 nssa default-information-originate

R3(config-router)#no area 2 nssa

*Mar 1 00:47:15.855: %OSPF-5-ADJCHG: Process 100, Nbr 4.4.4.4 on FastEthernet1/0 from FULL to DOWN, Neighbor Down: Adjacency forced to reset

R3(config-router)#area 2 nssa no-summary

*Mar 1 00:47:25.615: %OSPF-5-ADJCHG: Process 100, Nbr 4.4.4.4 on FastEthernet1/0 from DOWN to DOWN, Neighbor Down: Adjacency forced to reset

*Mar 1 00:47:29.935: %OSPF-5-ADJCHG: Process 100, Nbr 4.4.4.4 on FastEthernet1/0 from LOADING to FULL, Loading Done

R3(config-router)#exit

102.0.0.0/24 is subnetted, 1 subnets

O E2 102.1.1.0 [110/20] via 23.1.1.1, 00:01:33, FastEthernet0/0

1.0.0.0/32 is subnetted, 1 subnets

O IA 1.1.1.1 [110/3] via 23.1.1.1, 00:01:33, FastEthernet0/0

2.0.0.0/32 is subnetted, 1 subnets

O IA 2.2.2.2 [110/2] via 23.1.1.1, 00:01:33, FastEthernet0/0

100.0.0.0/24 is subnetted, 1 subnets

O E2 100.1.1.0 [110/20] via 23.1.1.1, 00:01:33, FastEthernet0/0

101.0.0.0/24 is subnetted, 1 subnets

O E2 101.1.1.0 [110/20] via 23.1.1.1, 00:01:33, FastEthernet0/0

4.0.0.0/32 is subnetted, 1 subnets

O 4.4.4.4 [110/2] via 34.1.1.2, 00:01:33, FastEthernet1/0

O N2 201.1.1.0/24 [110/20] via 34.1.1.2, 00:01:33, FastEthernet1/0

5.0.0.0/32 is subnetted, 1 subnets

O 5.5.5.5 [110/3] via 34.1.1.2, 00:01:33, FastEthernet1/0

O N2 200.1.1.0/24 [110/20] via 34.1.1.2, 00:01:33, FastEthernet1/0

O N2 202.1.1.0/24 [110/20] via 34.1.1.2, 00:01:33, FastEthernet1/0

12.0.0.0/24 is subnetted, 1 subnets

O IA 12.1.1.0 [110/2] via 23.1.1.1, 00:01:35, FastEthernet0/0

45.0.0.0/24 is subnetted, 1 subnets

O 45.1.1.0 [110/2] via 34.1.1.2, 00:01:35, FastEthernet1/0

R4#

O N2 201.1.1.0/24 [110/20] via 45.1.1.2, 00:02:23, FastEthernet1/0

O 5.5.5.5 [110/2] via 45.1.1.2, 00:02:23, FastEthernet1/0

O N2 200.1.1.0/24 [110/20] via 45.1.1.2, 00:02:23, FastEthernet1/0

O N2 202.1.1.0/24 [110/20] via 45.1.1.2, 00:02:23, FastEthernet1/0

O*IA 0.0.0.0/0 [110/2] via 34.1.1.1, 00:02:23, FastEthernet0/0

R5#

34.0.0.0/24 is subnetted, 1 subnets

O 34.1.1.0 [110/2] via 45.1.1.1, 00:03:01, FastEthernet0/0

4.0.0.0/32 is subnetted, 1 subnets

O 4.4.4.4 [110/2] via 45.1.1.1, 00:03:01, FastEthernet0/0

O*IA 0.0.0.0/0 [110/3] via 45.1.1.1, 00:03:01, FastEthernet0/0

當做了完全nssa區域之後，可以看到，原本的R5基於nssa區域的情況下，並沒有產生多大的變化，但是看R4上，優化掉了從左邊ABR傳過來的3類，4類，5類的LSA，從本區域的ASBR傳過來的OE2的條目被轉換為了ON2的路由條目，取而代之的是一條3類的O*IA的條目指向ABR，R5上同樣也是優化掉了從左邊ABR傳過來的3類，4，5類LSA，並且也產生了一條指向R4的O*IA的默認，實現了最大化的路由條目優化。

接下來再次測試：

R1#ping 200.1.1.1 source 100.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 200.1.1.1, timeout is 2 seconds:

Packet sent with a source address of 100.1.1.1

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 88/152/208 ms

可以通信，沒有問題，那麼Area1呢，這裡直接做完全nssa區域優化，在做之前，先簡單的查看一下R1和R2的路由表：

R1#

34.0.0.0/24 is subnetted, 1 subnets

O IA 34.1.1.0 [110/3] via 12.1.1.2, 00:00:40, FastEthernet0/0

2.0.0.0/32 is subnetted, 1 subnets

O 2.2.2.2 [110/2] via 12.1.1.2, 00:00:40, FastEthernet0/0

3.0.0.0/32 is subnetted, 1 subnets

O IA 3.3.3.3 [110/3] via 12.1.1.2, 00:00:40, FastEthernet0/0

4.0.0.0/32 is subnetted, 1 subnets

O IA 4.4.4.4 [110/4] via 12.1.1.2, 00:00:40, FastEthernet0/0

O E2 201.1.1.0/24 [110/20] via 12.1.1.2, 00:00:40, FastEthernet0/0

5.0.0.0/32 is subnetted, 1 subnets

O IA 5.5.5.5 [110/5] via 12.1.1.2, 00:00:40, FastEthernet0/0

O E2 200.1.1.0/24 [110/20] via 12.1.1.2, 00:00:40, FastEthernet0/0

23.0.0.0/24 is subnetted, 1 subnets

O IA 23.1.1.0 [110/2] via 12.1.1.2, 00:00:40, FastEthernet0/0

O E2 202.1.1.0/24 [110/20] via 12.1.1.2, 00:00:40, FastEthernet0/0

45.0.0.0/24 is subnetted, 1 subnets

O IA 45.1.1.0 [110/4] via 12.1.1.2, 00:00:40, FastEthernet0/0

R2#

34.0.0.0/24 is subnetted, 1 subnets

O IA 34.1.1.0 [110/2] via 23.1.1.2, 00:01:15, FastEthernet1/0

102.0.0.0/24 is subnetted, 1 subnets

O E2 102.1.1.0 [110/20] via 12.1.1.1, 00:01:15, FastEthernet0/0

1.0.0.0/32 is subnetted, 1 subnets

O 1.1.1.1 [110/2] via 12.1.1.1, 00:01:15, FastEthernet0/0

100.0.0.0/24 is subnetted, 1 subnets

O E2 100.1.1.0 [110/20] via 12.1.1.1, 00:01:15, FastEthernet0/0

3.0.0.0/32 is subnetted, 1 subnets

O 3.3.3.3 [110/2] via 23.1.1.2, 00:01:15, FastEthernet1/0

101.0.0.0/24 is subnetted, 1 subnets

O E2 101.1.1.0 [110/20] via 12.1.1.1, 00:01:15, FastEthernet0/0

4.0.0.0/32 is subnetted, 1 subnets

O IA 4.4.4.4 [110/3] via 23.1.1.2, 00:01:15, FastEthernet1/0

O E2 201.1.1.0/24 [110/20] via 23.1.1.2, 00:01:15, FastEthernet1/0

5.0.0.0/32 is subnetted, 1 subnets

O IA 5.5.5.5 [110/4] via 23.1.1.2, 00:01:15, FastEthernet1/0

O E2 200.1.1.0/24 [110/20] via 23.1.1.2, 00:01:15, FastEthernet1/0

O E2 202.1.1.0/24 [110/20] via 23.1.1.2, 00:01:16, FastEthernet1/0

45.0.0.0/24 is subnetted, 1 subnets

O IA 45.1.1.0 [110/3] via 23.1.1.2, 00:01:16, FastEthernet1/0

可以看到，一大堆的路由條目，那麼接下來開始配置：

R1(config)#router ospf 100

R1(config-router)#area 1 nssa

R1(config)#end

R2(config)#router ospf 100

R2(config-router)#area 1 nssa no-summary

R2(config-router)#end

配置後的路由信息：

R1#

2.0.0.0/32 is subnetted, 1 subnets

O 2.2.2.2 [110/2] via 12.1.1.2, 00:01:21, FastEthernet0/0

O*IA 0.0.0.0/0 [110/2] via 12.1.1.2, 00:01:21, FastEthernet0/0

R2#

34.0.0.0/24 is subnetted, 1 subnets

O IA 34.1.1.0 [110/2] via 23.1.1.2, 00:02:22, FastEthernet1/0

102.0.0.0/24 is subnetted, 1 subnets

O N2 102.1.1.0 [110/20] via 12.1.1.1, 00:02:22, FastEthernet0/0

1.0.0.0/32 is subnetted, 1 subnets

O 1.1.1.1 [110/2] via 12.1.1.1, 00:02:22, FastEthernet0/0

100.0.0.0/24 is subnetted, 1 subnets

O N2 100.1.1.0 [110/20] via 12.1.1.1, 00:02:22, FastEthernet0/0

3.0.0.0/32 is subnetted, 1 subnets

O 3.3.3.3 [110/2] via 23.1.1.2, 00:02:32, FastEthernet1/0

101.0.0.0/24 is subnetted, 1 subnets

O N2 101.1.1.0 [110/20] via 12.1.1.1, 00:02:22, FastEthernet0/0

4.0.0.0/32 is subnetted, 1 subnets

O IA 4.4.4.4 [110/3] via 23.1.1.2, 00:02:22, FastEthernet1/0

O E2 201.1.1.0/24 [110/20] via 23.1.1.2, 00:02:22, FastEthernet1/0

5.0.0.0/32 is subnetted, 1 subnets

O IA 5.5.5.5 [110/4] via 23.1.1.2, 00:02:22, FastEthernet1/0

O E2 200.1.1.0/24 [110/20] via 23.1.1.2, 00:02:22, FastEthernet1/0

O E2 202.1.1.0/24 [110/20] via 23.1.1.2, 00:02:24, FastEthernet1/0

45.0.0.0/24 is subnetted, 1 subnets

O IA 45.1.1.0 [110/3] via 23.1.1.2, 00:02:24, FastEthernet1/0

可以看到，R2上雖然變化並不大，但是在R1上，優化掉了3，4，5類的LSA，由10條路由條目變為了2條路由條目，並且產生了一條O*IA的默認，指向ABR。

至此，nssa區域的優化示例結束，歡迎大家共同探討技術問題，關注瞭解更多，thank you !

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