1.只有NSSA区域中才会现LSA7，可以存在ASBR,阻止LSA4/5

2.ABR将LSA7转成LSA5，传播到其他区域,这时，ABR也成为了ASBR，因为它也引入了LSA5,其它路由器看到LSA5的通告路由器是ABR。

 

 

二、实验拓扑如下:R1到R2属区域0，R2到R3属区域1并配置为NSSA区域，R1与R3分别运行RIP与EIGRP模拟OSPF外部路由,接口与IP地址信息如下所示.

 

R1:

Router>
Router>en
Router#conf t
Router(config)#hostname R1
R1(config-line)#exit
R1(config)#interface f0/0
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#no sh
R1(config-if)#exit
R1(config)#interface loopback 0
R1(config-if)#ip address 1.1.1.1 255.255.255.0
R1(config-if)#ip ospf network point-to-point    //防止学习32位的主机路由
R1(config-if)#int lo1
R1(config-if)#ip address 1.1.2.1 255.255.255.0
R1(config-if)#ip ospf network point-to-point    //防止学习32位的主机路由
R1(config-if)#exit
R1(config)#router ospf 1        //启用OSPF路由协议
R1(config-router)#router-id 1.1.1.1    //指定ROUTE-ID
R1(config-router)#network 192.168.1.1 0.0.0.0 area 0    //发布网段到区域0
R1(config-router)#exit
R1(config)#router rip     //启用RIP路由协议
R1(config-router)#version 2     //指定版本2
R1(config-router)#no auto-summary     //不要自动汇总
R1(config-router)#network 1.1.1.0    //发布网段
R1(config-router)#network 1.1.2.0    //同上
R1(config-router)#end
R1#

 

R2:

start
Router>
Router>en
Router#conf t
Router(config)#hostname R2
R2(config)#interface f0/0
R2(config-if)#ip address 192.168.1.2 255.255.255.0
R2(config-if)#no sh
R2(config-if)#exit
R2(config)#interface f0/1
R2(config-if)#ip address 192.168.2.2 255.255.255.0
R2(config-if)#no sh
R2(config-if)#exit
R2(config)#interface loopback 0
R2(config-if)#ip address 2.2.1.1 255.255.255.0
R2(config-if)#ip ospf network point-to-point 
R2(config-if)#int lo1
R2(config-if)#ip address 2.2.2.1 255.255.255.0
R2(config-if)#ip ospf network point-to-point 
R2(config-if)#exit
R2(config)#router ospf 1     //启用OSPF路由协议
R2(config-router)#router-id 2.2.2.2     //同上
R2(config-router)#network 192.168.1.2 0.0.0.0 area 0
R2(config-router)#network 192.168.2.2 0.0.0.0 area 1
R2(config-router)#network 2.2.1.1 0.0.0.0 area 0    
R2(config-router)#network 2.2.2.1 0.0.0.0 area 0
R2(config-router)#end     
R2#

 

R3:

Router>
Router>en
Router#conf t
Router(config)#hostname R3
R3(config)#interface f0/1
R3(config-if)#ip address 192.168.2.1 255.255.255.0
R3(config-if)#no sh
R3(config-if)#exit
R3(config)#interface loopback 0
R3(config-if)#ip address 172.16.1.1 255.255.255.0
R3(config-if)#int lo1
R3(config-if)#ip address 172.16.2.1 255.255.255.0
R3(config-if)#exit
R3(config)#router ospf 1     //启用OSPF路由协议
R3(config-router)#router-id 3.3.3.3     //同上
R3(config-router)#network 192.168.2.1 0.0.0.0 area 1
R3(config-router)#exit 
R3(config)#router eigrp 1
R3(config-router)#no auto-summary 
R3(config-router)#network 172.16.1.0 0.0.0.255
R3(config-router)#network 172.16.2.0 0.0.0.255
R3(config-router)#end
R3#

 

 

 

 

R1(config)#router ospf 1
R1(config-router)#redistribute rip subnets    //将RIP重发布进OSPF
R1(config-router)#exit
R1(config)#router rip
R1(config-router)#redistribute ospf 1 metric 1     //将OSPF重发布进RIP度量为1
R1(config-router)#end
R1#

R3(config)#router ospf 1
R3(config-router)#redistribute eigrp 1 subnets     //将EIGRP重发布进OSPF
R3(config-router)#exit
R3(config)#router eigrp 1
R3(config-router)#redistribute ospf 1 metric 100000 5 255 1 1500
//将OSPF重发布进EIGRP，带宽=100000KM 廷迟=5 可靠性=255 负载=1 最大传输单元=1500
R3(config-router)#end
R3#

 

 

步骤三：将区域1配置为NSSA区域.

 

R2(config)#router ospf 1
R2(config-router)#area 1 nssa     //将区域1配置为NSSA
R2(config-router)#end
R2#

R3(config)#router ospf 1
R3(config-router)#area 1 nssa     //将区域1配置为NSSA
R3(config-router)#end
R3#

 

 

步骤四：在R1，R2与R3上分别验证

 

查看R1路由表：
R1#show ip route 
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
       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

Gateway of last resort is not set

     1.0.0.0/24 is subnetted, 2 subnets
C       1.1.1.0 is directly connected, Loopback0
C       1.1.2.0 is directly connected, Loopback1
     2.0.0.0/24 is subnetted, 2 subnets
O       2.2.1.0 [110/2] via 192.168.1.2, 00:08:29, FastEthernet0/0
O       2.2.2.0 [110/2] via 192.168.1.2, 00:08:29, FastEthernet0/0
     172.16.0.0/24 is subnetted, 2 subnets
O E2    172.16.1.0 [110/20] via 192.168.1.2, 00:07:34, FastEthernet0/0
O E2    172.16.2.0 [110/20] via 192.168.1.2, 00:07:34, FastEthernet0/0
C    192.168.1.0/24 is directly connected, FastEthernet0/0
O IA 192.168.2.0/24 [110/2] via 192.168.1.2, 00:08:04, FastEthernet0/0
R1#     
//R1上可以学习到所有路由，因为它是正常区域，没有做任何配置，可以学习所以类型的LSA

 

查看R2路由表：
R2#show ip route 
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
       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

Gateway of last resort is not set

     1.0.0.0/24 is subnetted, 2 subnets
O E2    1.1.1.0 [110/20] via 192.168.1.1, 00:04:19, FastEthernet0/0
O E2    1.1.2.0 [110/20] via 192.168.1.1, 00:04:19, FastEthernet0/0
     2.0.0.0/24 is subnetted, 2 subnets
C       2.2.1.0 is directly connected, Loopback0
C       2.2.2.0 is directly connected, Loopback1
     172.16.0.0/24 is subnetted, 2 subnets
O N2    172.16.1.0 [110/20] via 192.168.2.1, 00:04:19, FastEthernet0/1
O N2    172.16.2.0 [110/20] via 192.168.2.1, 00:04:19, FastEthernet0/1
C    192.168.1.0/24 is directly connected, FastEthernet0/0
C    192.168.2.0/24 is directly connected, FastEthernet0/1
R2#
//有人肯定会说NSSA区域不是不会学习5类LSA吗，怎么多了2条E2的路由？
因为R2是NSSA的ABR，它所要做的事情就是将7类型LSA转成5类LSA并传播到区域间每个路由器，还有NSSA区域可以学习本区域引入的外部路由，上面两条N2的路由为从R3上EIGRP所学的外部路由.

查看R3路由表：
R3#show ip route 
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
       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

Gateway of last resort is not set

     2.0.0.0/24 is subnetted, 2 subnets
O IA    2.2.1.0 [110/2] via 192.168.2.2, 00:13:21, FastEthernet0/1
O IA    2.2.2.0 [110/2] via 192.168.2.2, 00:13:21, FastEthernet0/1
     172.16.0.0/24 is subnetted, 2 subnets
C       172.16.1.0 is directly connected, Loopback0
C       172.16.2.0 is directly connected, Loopback1
O IA 192.168.1.0/24 [110/2] via 192.168.2.2, 00:13:21, FastEthernet0/1
C    192.168.2.0/24 is directly connected, FastEthernet0/1
R3#
//R3属于NSSA区域内，而非NSSA区域ABR，所以它就验证了NSSA区域不能学习其它区域引入的外部路由。

 

 

 

疑问：为什么在R2上面会发生7类LSA转5类LSA？
我们来看看R2的OSPF链路状态数据库:
R2#show ip ospf database

                Type-7 AS External Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Tag
172.16.1.0      3.3.3.3         1501        0x80000001 0x00C09F 0
172.16.2.0      3.3.3.3         1501        0x80000001 0x00B5A9 0

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
1.1.1.0         1.1.1.1         483         0x80000002 0x00A3F4 0
1.1.2.0         1.1.1.1         484         0x80000002 0x0098FE 0
172.16.1.0      2.2.2.2         1495        0x80000001 0x0073FA 0
172.16.2.0      2.2.2.2         1495        0x80000001 0x006805 0
R2#

注：前面说过，只有NSSA区域存放7类LSA，所以7类LSA传播到其它区域根本就不识别，仔细看R2上5类与7类LSA的摘要，都存放了172.16.1.0与172.16.2.0，所以这就7类变5类LSA的转折点.