试验目的：熟悉OSPF的特殊区域：NSSA
使用拓扑：
NSSA区域：
说明R5上也起一个LO1接口：Ip地址为100.100.100.100，然后充分布进R5这样R5也就成为了ASBR，
将R1,R2上配置area 1 nssa后，
R2#show ip route os
200.200.200.0/32 is subnetted, 1 subnets
O N2 200.200.200.200 [110/20] via 10.1.12.1, 00:03:17, Serial1/0
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/65] via 10.1.12.1, 00:03:17, Serial1/0
100.0.0.0/32 is subnetted, 1 subnets
O E2 100.100.100.100 [110/20] via 10.1.23.3, 00:03:17, Serial1/1
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/65] via 10.1.23.3, 00:03:17, Serial1/1
4.0.0.0/32 is subnetted, 1 subnets
O IA 4.4.4.4 [110/129] via 10.1.23.3, 00:03:17, Serial1/1
5.0.0.0/32 is subnetted, 1 subnets
O IA 5.5.5.5 [110/193] via 10.1.23.3, 00:03:17, Serial1/1
10.0.0.0/24 is subnetted, 4 subnets
O IA 10.1.45.0 [110/192] via 10.1.23.3, 00:03:17, Serial1/1
O 10.1.34.0 [110/128] via 10.1.23.3, 00:03:17, Serial1/1
R2#show ip ospf database
OSPF Router with ID (2.2.2.2) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 23 0x80000005 0x008FAB 2
3.3.3.3 3.3.3.3 1888 0x80000006 0x003AD4 5
4.4.4.4 4.4.4.4 935 0x80000005 0x008490 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
1.1.1.1 2.2.2.2 8 0x80000001 0x00AB44
2.2.2.2 2.2.2.2 1354 0x80000003 0x00F633
4.4.4.4 4.4.4.4 930 0x80000002 0x0060BA
5.5.5.5 4.4.4.4 159 0x80000001 0x00B621
10.1.12.0 2.2.2.2 1354 0x80000003 0x00B823
10.1.45.0 4.4.4.4 930 0x80000002 0x0012A1
Summary ASB Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
5.5.5.5 4.4.4.4 86 0x80000001 0x009E39
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 17 0x8000000C 0x000934 3
2.2.2.2 2.2.2.2 17 0x8000000B 0x003004 3
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
3.3.3.3 2.2.2.2 24 0x80000003 0x00F0EE
4.4.4.4 2.2.2.2 24 0x80000002 0x004755
5.5.5.5 2.2.2.2 24 0x80000002 0x009BBC
10.1.23.0 2.2.2.2 24 0x80000003 0x00E4E5
10.1.34.0 2.2.2.2 24 0x80000003 0x00ED91
10.1.45.0 2.2.2.2 24 0x80000002 0x00F83C
Type-7 AS External Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Tag
200.200.200.200 1.1.1.1 42 0x80000001 0x005318 0
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
100.100.100.100 5.5.5.5 92 0x80000001 0x0047B3 0
200.200.200.200 2.2.2.2 3 0x80000001 0x00C9A7 0
R1#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 10 0x8000000C 0x000934 3
2.2.2.2 2.2.2.2 11 0x8000000B 0x003004 3
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
3.3.3.3 2.2.2.2 18 0x80000003 0x00F0EE
4.4.4.4 2.2.2.2 18 0x80000002 0x004755
5.5.5.5 2.2.2.2 18 0x80000002 0x009BBC
10.1.23.0 2.2.2.2 18 0x80000003 0x00E4E5
10.1.34.0 2.2.2.2 18 0x80000003 0x00ED91
10.1.45.0 2.2.2.2 18 0x80000002 0x00F83C
Type-7 AS External Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Tag
200.200.200.200 1.1.1.1 34 0x80000001 0x005318 0
R1#ping 100.100.100.100
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 100.100.100.100, timeout is 2 seconds:
.....为什么不通呢？因为没有到200.200.200.200的路由
在R5上R5#p 200.200.200.200
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 200.200.200.200, timeout is 2 seconds:
!!!!!他能通是因为回程路由的地址是R5的出接口地址10.1.45.5，在R1上有这个路由，所以能通。
在R1上没有回程的路由，该怎么解决呢，这个就需要在R2上指定一个回程的默认路由给R1：
R2(config-router)#area 1 nssa default-information-originate
此时在看R1上的路由表：
R1#show ip route os
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 10.1.12.2, 00:12:22, Serial1/1
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [110/129] via 10.1.12.2, 00:12:22, Serial1/1
4.0.0.0/32 is subnetted, 1 subnets
O IA 4.4.4.4 [110/193] via 10.1.12.2, 00:12:22, Serial1/1
5.0.0.0/32 is subnetted, 1 subnets
O IA 5.5.5.5 [110/257] via 10.1.12.2, 00:12:22, Serial1/1
10.0.0.0/24 is subnetted, 4 subnets
O IA 10.1.23.0 [110/128] via 10.1.12.2, 00:12:22, Serial1/1
O IA 10.1.45.0 [110/256] via 10.1.12.2, 00:12:22, Serial1/1
O IA 10.1.34.0 [110/192] via 10.1.12.2, 00:12:22, Serial1/1
O*N2 0.0.0.0/0 [110/1] via 10.1.12.2, 00:10:25, Serial1/1
总结：NSSA区域是不能有LSA5产生的，但是由于存在ASBR，他必定会产生LSA5，这样怎么办呢，这个就产生了一个新的区域类型：NSSA，他允许ASBR产生外部的LSA7,在连接到骨干区域的路由器将其转换成LSA5（因为骨干区域不能识别LSA7），从而也就不能通告给其他区域了，在这个拓扑中，完成这个转换的是R2（他既是ABR又是ASBR）
R2#show ip ospf database router 2.2.2.2
OSPF Router with ID (2.2.2.2) (Process ID 1)
Router Link States (Area 0)
LS age: 1018
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 2.2.2.2
Advertising Router: 2.2.2.2
LS Seq Number: 80000005
Checksum: 0x8FAB
Length: 48
Area Border Router
AS Boundary Router //因为将外部的LSA转换成了LSA5,所以他也就成了双重身份。
在R2上R2(config-router)#area 1 nssa no-summary （不通告LSA3）后，R1的路由表条目更加的少了：
R1# show ip route os
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 10.1.12.2, 00:27:48, Serial1/1
O*IA 0.0.0.0/0 [110/65] via 10.1.12.2, 00:01:18, Serial1/1
如果在R2上做了一下配置的话;
R2(config-router)#int lo1
R2(config-if)#ip add 22.22.22.22 255.255.255.255
R2(config-if)#router rip
R2(config-router)#ver 2
R2(config-router)#no au
R2(config-router)#net 22.0.0.0
R2(config-router)#redistribute rip subnets
在R1上的数据库会产生
Type-7 AS External Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Tag
0.0.0.0 2.2.2.2 88 0x80000002 0x00336D 0
22.22.22.22 2.2.2.2 2 0x80000001 0x00FB3A 0
200.200.200.200 1.1.1.1 245 0x80000002 0x005119 0
R1#show ip route os
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 10.1.12.2, 00:35:27, Serial1/1
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [110/129] via 10.1.12.2, 00:05:06, Serial1/1
4.0.0.0/32 is subnetted, 1 subnets
O IA 4.4.4.4 [110/193] via 10.1.12.2, 00:05:06, Serial1/1
5.0.0.0/32 is subnetted, 1 subnets
O IA 5.5.5.5 [110/257] via 10.1.12.2, 00:05:06, Serial1/1
22.0.0.0/32 is subnetted, 1 subnets
O N2 22.22.22.22 [110/20] via 10.1.12.2, 00:01:49, Serial1/1
10.0.0.0/24 is subnetted, 4 subnets
O IA 10.1.23.0 [110/128] via 10.1.12.2, 00:05:06, Serial1/1
O IA 10.1.45.0 [110/256] via 10.1.12.2, 00:05:06, Serial1/1
O IA 10.1.34.0 [110/192] via 10.1.12.2, 00:05:06, Serial1/1
O*N2 0.0.0.0/0 [110/1] via 10.1.12.2, 00:05:01, Serial1/1
然而在R2上做了如下配置后：
R2(config-router)#area 1 nssa no-redistribution
R1上的路由表中将缺少22.22.22.22的路由，到达外部的路由全部走缺省的路由条目。
R1#show ip route os
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 10.1.12.2, 00:36:56, Serial1/1
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [110/129] via 10.1.12.2, 00:06:35, Serial1/1
4.0.0.0/32 is subnetted, 1 subnets
O IA 4.4.4.4 [110/193] via 10.1.12.2, 00:06:35, Serial1/1
5.0.0.0/32 is subnetted, 1 subnets
O IA 5.5.5.5 [110/257] via 10.1.12.2, 00:06:35, Serial1/1
10.0.0.0/24 is subnetted, 4 subnets
O IA 10.1.23.0 [110/128] via 10.1.12.2, 00:06:35, Serial1/1
O IA 10.1.45.0 [110/256] via 10.1.12.2, 00:06:35, Serial1/1
O IA 10.1.34.0 [110/192] via 10.1.12.2, 00:06:35, Serial1/1
O*N2 0.0.0.0/0 [110/1] via 10.1.12.2, 00:06:30, Serial1/1
本文转自 gehailong 51CTO博客，原文链接：http://blog.51cto.com/gehailong/297394，如需转载请自行联系原作者
