ospf nssa区域4类lsa的问题
ospf nssa区域4类lsa的问题：
拓扑
r1----r5----r2
首先将r1与r5的链路配置在区域1中，将r5与r2的链路配置在区域0中，配置几个r1的loopback地址做测试，r5上show ip route和show ip ospf database如下：
R5#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, 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
1.0.0.0/32 is subnetted, 1 subnets
O E2 1.1.1.1 [110/20] via 192.168.1.1, 00:04:24, Serial0/0
5.0.0.0/32 is subnetted, 1 subnets
C 5.5.5.5 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 3 subnets
O E2 10.1.3.0 [110/20] via 192.168.1.1, 00:04:24, Serial0/0
O E2 10.1.2.0 [110/20] via 192.168.1.1, 00:04:24, Serial0/0
O E2 10.1.1.0 [110/20] via 192.168.1.1, 00:04:24, Serial0/0
192.168.1.0/30 is subnetted, 2 subnets
C 192.168.1.0 is directly connected, Serial0/0
C 192.168.1.4 is directly connected, Serial0/1
R5#show ip ospf database
OSPF Router with ID (5.5.5.5) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 300 0x80000002 0x8221 2
5.5.5.5 5.5.5.5 300 0x80000002 0x2C6B 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.1.0 5.5.5.5 321 0x80000001 0xA6DA
Summary ASB Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.10.10.10 5.5.5.5 296 0x80000001 0x9926
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
5.5.5.5 5.5.5.5 317 0x80000003 0xB8C4 2
10.10.10.10 10.10.10.10 298 0x80000003 0x85E3 2
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.1.4 5.5.5.5 312 0x80000001 0x7EFE
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.1 10.10.10.10 288 0x80000001 0x8CE7 0
10.1.1.0 10.10.10.10 288 0x80000001 0x214B 0
10.1.2.0 10.10.10.10 288 0x80000001 0x1655 0
10.1.3.0 10.10.10.10 288 0x80000001 0xB5F 0
可以看到有4类的lsa，link ID为r1的router-id，ADV Router为r5的router-id，表明是由r5产生的这个4类的lsa，用于指定asbr的router-id的地址，然后查看r2的lsa：
R5#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, 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
1.0.0.0/32 is subnetted, 1 subnets
O N2 1.1.1.1 [110/20] via 192.168.1.1, 00:00:01, Serial0/0
5.0.0.0/32 is subnetted, 1 subnets
C 5.5.5.5 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 3 subnets
O N2 10.1.3.0 [110/20] via 192.168.1.1, 00:00:01, Serial0/0
O N2 10.1.2.0 [110/20] via 192.168.1.1, 00:00:01, Serial0/0
O N2 10.1.1.0 [110/20] via 192.168.1.1, 00:00:01, Serial0/0
192.168.1.0/30 is subnetted, 2 subnets
C 192.168.1.0 is directly connected, Serial0/0
C 192.168.1.4 is directly connected, Serial0/1
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 2.2.2.2 484 0x80000002 0x8221 2
5.5.5.5 5.5.5.5 484 0x80000002 0x2C6B 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.1.0 5.5.5.5 505 0x80000001 0xA6DA
Summary ASB Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.10.10.10 5.5.5.5 480 0x80000001 0x9926
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.1 10.10.10.10 471 0x80000001 0x8CE7 0
10.1.1.0 10.10.10.10 472 0x80000001 0x214B 0
10.1.2.0 10.10.10.10 472 0x80000001 0x1655 0
10.1.3.0 10.10.10.10 472 0x80000001 0xB5F 0
也具有4类lsa，并且在5类lsa中link ID是asbr重发布过来的地址，ADV Router全部都是r1的router-id，说明as外部地址都是通过r1学到的,而r1可以通过r5到达。
下面把area 1配置成为nssa区域，然后在观察r5的show ip route和show ip ospf database：
R5#show ip ospf database
OSPF Router with ID (5.5.5.5) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 746 0x80000002 0x8221 2
5.5.5.5 5.5.5.5 16 0x80000003 0x3064 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.1.0 5.5.5.5 767 0x80000001 0xA6DA
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
5.5.5.5 5.5.5.5 10 0x80000005 0x6013 2
10.10.10.10 10.10.10.10 9 0x80000005 0x273A 2
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.1.4 5.5.5.5 16 0x80000002 0x2254
Type-7 AS External Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.1 10.10.10.10 14 0x80000001 0x43BB 0
10.1.1.0 10.10.10.10 14 0x80000001 0xD71F 0
10.1.2.0 10.10.10.10 14 0x80000001 0xCC29 0
10.1.3.0 10.10.10.10 14 0x80000001 0xC133 0
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.1 5.5.5.5 6 0x80000001 0x6EAE 0
10.1.1.0 5.5.5.5 6 0x80000001 0x312 0
10.1.2.0 5.5.5.5 6 0x80000001 0xF71C 0
10.1.3.0 5.5.5.5 6 0x80000001 0xEC26 0
通过路由表和lsa数据库可以看到r5将7类lsa转变成为5类的lsa，注意在转变成为5类lsa的时候ADV Router变为r5的router-id了，再看一下r2的lsa数据库：
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 2.2.2.2 904 0x80000002 0x8221 2
5.5.5.5 5.5.5.5 175 0x80000003 0x3064 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.1.0 5.5.5.5 926 0x80000001 0xA6DA
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.1 5.5.5.5 164 0x80000001 0x6EAE 0
10.1.1.0 5.5.5.5 164 0x80000001 0x312 0
10.1.2.0 5.5.5.5 164 0x80000001 0xF71C 0
10.1.3.0 5.5.5.5 164 0x80000001 0xEC26 0
也同样没有4类lsa了，看一下5类lsa中所有链路地址都是通过r5学到的，所以也就不需要知道真正asbr的位置在哪，只需要把数据转发给r5，由r5根据路由表转发给asbr就可以了，这就是没有4类lsa的原因了。
PS：TCP/IP路由卷一中讲述ospf nssa区域的时候说nssa不拒绝4类lsa，是错误的，看的时候请注意更正！
拓扑
r1----r5----r2
首先将r1与r5的链路配置在区域1中，将r5与r2的链路配置在区域0中，配置几个r1的loopback地址做测试，r5上show ip route和show ip ospf database如下：
R5#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, 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
1.0.0.0/32 is subnetted, 1 subnets
O E2 1.1.1.1 [110/20] via 192.168.1.1, 00:04:24, Serial0/0
5.0.0.0/32 is subnetted, 1 subnets
C 5.5.5.5 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 3 subnets
O E2 10.1.3.0 [110/20] via 192.168.1.1, 00:04:24, Serial0/0
O E2 10.1.2.0 [110/20] via 192.168.1.1, 00:04:24, Serial0/0
O E2 10.1.1.0 [110/20] via 192.168.1.1, 00:04:24, Serial0/0
192.168.1.0/30 is subnetted, 2 subnets
C 192.168.1.0 is directly connected, Serial0/0
C 192.168.1.4 is directly connected, Serial0/1
R5#show ip ospf database
OSPF Router with ID (5.5.5.5) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 300 0x80000002 0x8221 2
5.5.5.5 5.5.5.5 300 0x80000002 0x2C6B 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.1.0 5.5.5.5 321 0x80000001 0xA6DA
Summary ASB Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.10.10.10 5.5.5.5 296 0x80000001 0x9926
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
5.5.5.5 5.5.5.5 317 0x80000003 0xB8C4 2
10.10.10.10 10.10.10.10 298 0x80000003 0x85E3 2
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.1.4 5.5.5.5 312 0x80000001 0x7EFE
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.1 10.10.10.10 288 0x80000001 0x8CE7 0
10.1.1.0 10.10.10.10 288 0x80000001 0x214B 0
10.1.2.0 10.10.10.10 288 0x80000001 0x1655 0
10.1.3.0 10.10.10.10 288 0x80000001 0xB5F 0
可以看到有4类的lsa，link ID为r1的router-id，ADV Router为r5的router-id，表明是由r5产生的这个4类的lsa，用于指定asbr的router-id的地址，然后查看r2的lsa：
R5#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, 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
1.0.0.0/32 is subnetted, 1 subnets
O N2 1.1.1.1 [110/20] via 192.168.1.1, 00:00:01, Serial0/0
5.0.0.0/32 is subnetted, 1 subnets
C 5.5.5.5 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 3 subnets
O N2 10.1.3.0 [110/20] via 192.168.1.1, 00:00:01, Serial0/0
O N2 10.1.2.0 [110/20] via 192.168.1.1, 00:00:01, Serial0/0
O N2 10.1.1.0 [110/20] via 192.168.1.1, 00:00:01, Serial0/0
192.168.1.0/30 is subnetted, 2 subnets
C 192.168.1.0 is directly connected, Serial0/0
C 192.168.1.4 is directly connected, Serial0/1
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 2.2.2.2 484 0x80000002 0x8221 2
5.5.5.5 5.5.5.5 484 0x80000002 0x2C6B 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.1.0 5.5.5.5 505 0x80000001 0xA6DA
Summary ASB Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.10.10.10 5.5.5.5 480 0x80000001 0x9926
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.1 10.10.10.10 471 0x80000001 0x8CE7 0
10.1.1.0 10.10.10.10 472 0x80000001 0x214B 0
10.1.2.0 10.10.10.10 472 0x80000001 0x1655 0
10.1.3.0 10.10.10.10 472 0x80000001 0xB5F 0
也具有4类lsa，并且在5类lsa中link ID是asbr重发布过来的地址，ADV Router全部都是r1的router-id，说明as外部地址都是通过r1学到的,而r1可以通过r5到达。
下面把area 1配置成为nssa区域，然后在观察r5的show ip route和show ip ospf database：
R5#show ip ospf database
OSPF Router with ID (5.5.5.5) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 746 0x80000002 0x8221 2
5.5.5.5 5.5.5.5 16 0x80000003 0x3064 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.1.0 5.5.5.5 767 0x80000001 0xA6DA
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
5.5.5.5 5.5.5.5 10 0x80000005 0x6013 2
10.10.10.10 10.10.10.10 9 0x80000005 0x273A 2
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
192.168.1.4 5.5.5.5 16 0x80000002 0x2254
Type-7 AS External Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.1 10.10.10.10 14 0x80000001 0x43BB 0
10.1.1.0 10.10.10.10 14 0x80000001 0xD71F 0
10.1.2.0 10.10.10.10 14 0x80000001 0xCC29 0
10.1.3.0 10.10.10.10 14 0x80000001 0xC133 0
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.1 5.5.5.5 6 0x80000001 0x6EAE 0
10.1.1.0 5.5.5.5 6 0x80000001 0x312 0
10.1.2.0 5.5.5.5 6 0x80000001 0xF71C 0
10.1.3.0 5.5.5.5 6 0x80000001 0xEC26 0
通过路由表和lsa数据库可以看到r5将7类lsa转变成为5类的lsa，注意在转变成为5类lsa的时候ADV Router变为r5的router-id了，再看一下r2的lsa数据库：
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 2.2.2.2 904 0x80000002 0x8221 2
5.5.5.5 5.5.5.5 175 0x80000003 0x3064 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.1.0 5.5.5.5 926 0x80000001 0xA6DA
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
1.1.1.1 5.5.5.5 164 0x80000001 0x6EAE 0
10.1.1.0 5.5.5.5 164 0x80000001 0x312 0
10.1.2.0 5.5.5.5 164 0x80000001 0xF71C 0
10.1.3.0 5.5.5.5 164 0x80000001 0xEC26 0
也同样没有4类lsa了，看一下5类lsa中所有链路地址都是通过r5学到的，所以也就不需要知道真正asbr的位置在哪，只需要把数据转发给r5，由r5根据路由表转发给asbr就可以了，这就是没有4类lsa的原因了。
PS：TCP/IP路由卷一中讲述ospf nssa区域的时候说nssa不拒绝4类lsa，是错误的，看的时候请注意更正！