课题内容:

将 area 1 配置为stub和totally stub区域,观察链路状态数据库及路由表

将 area 2 配置为nssa和totally nssa区域,观察链路状态数据库及路由表

配置强制由R1执行7转5的动作

在R4上将环回口重分布进OSPF特殊区域2,不允许该路由信息进入骨干区域

在R2上向特殊区域2内注入默认路由,该默认路由仅仅允许在特殊区域2内存在

拓扑图:

OSPF特殊区域研究_CCIE培训

接上回,将area 1 配置为stub和totally stub区域

Stub:

R5(config)#router ospf 110

R5(config-router)#area 1 stub

R3(config)#router ospf 110

R3(config-router)#area 1 stub

观察链路状态数据库及路由表

R5#show ip route ospf | begin Gateway

Gateway of last resort is 10.1.35.3 to network 0.0.0.0

O*IA 0.0.0.0/0 [110/11] via 10.1.35.3, 00:00:23, Ethernet0/3

10.0.0.0/8 is variably subnetted, 6 subnets, 2 masks

O IA 10.1.1.1/32 [110/74] via 10.1.35.3, 00:00:23, Ethernet0/3

O IA 10.1.1.3/32 [110/10] via 10.1.35.3, 00:00:23, Ethernet0/3

O IA 10.1.1.4/32 [110/74] via 10.1.35.3, 00:00:23, Ethernet0/3

O IA 10.1.124.0/24 [110/84] via 10.1.35.3, 00:00:23, Ethernet0/3

172.16.0.0/32 is subnetted, 5 subnets

O IA 172.16.1.1 [110/75] via 10.1.35.3, 00:00:23, Ethernet0/3

O IA 172.16.1.2 [110/85] via 10.1.35.3, 00:00:23, Ethernet0/3

O IA 172.16.1.3 [110/11] via 10.1.35.3, 00:00:23, Ethernet0/3

O IA 172.16.1.4 [110/75] via 10.1.35.3, 00:00:23, Ethernet0/3

// R5上没有收到来自R2重分布进OSPF的外部路由 //

证明了 stub区域是不允许五类LSA进入的;

收到了一个来自ABR生成的三类LSA,内容为一条默认路由的链路状态;

Totally Stub:

R3(config)#router ospf 110

R3(config-router)#area 1 stub no-summary

验证:

R5#show ip route ospf | begin Gateway

Gateway of last resort is 10.1.35.3 to network 0.0.0.0

O*IA 0.0.0.0/0 [110/11] via 10.1.35.3, 00:00:15, Ethernet0/3

// area 1 的区域内路由器在刚才的基础之上,路由器再次精简了,其中OSPF的路由只剩下一条默认了;

将 area 2 配置为nssa和totally nssa区域

Nssa:

R2(config)#router ospf 110

R2(config-router)#area 2 nssa

R1(config)#router ospf 110

R1(config-router)#area 2 nssa

R4(config)#router ospf 110

R4(config-router)#area 2 nssa

验证:

R2#show ip ospf database | begin Type-7

Type-7 AS External Link States (Area 2)

Link ID ADV Router Age Seq# Checksum Tag

10.2.0.0 172.16.1.2 57 0x80000001 0x0059B4 0

R2#show ip ospf database nssa-external

OSPF Router with ID (172.16.1.2) (Process ID 110)

Type-7 AS External Link States (Area 2)

LS age: 87

Options: (No TOS-capability, Type 7/5 translation, DC, Upward)

LS Type: AS External Link

Link State ID: 10.2.0.0 (External Network Number )

Advertising Router: 172.16.1.2

LS Seq Number: 80000001

Checksum: 0x59B4

Length: 36

Network Mask: /22

Metric Type: 2 (Larger than any link state path)

MTID: 0

Metric: 20

Forward Address: 172.16.1.2

External Route Tag: 0

转发地址字段,选举自ASBR设备上最大的环回口IP地址;

R1#show ip route ospf | include O N

O N2 10.2.0.0/22 [110/20] via 10.1.124.2, 00:03:17, Ethernet0/1

R3#show ip route ospf | include O E

O E2 10.2.0.0/22 [110/20] via 10.1.1.4, 00:03:47, Serial1/2

R3#show ip ospf database external

OSPF Router with ID (172.16.1.3) (Process ID 110)

Type-5 AS External Link States

Routing Bit Set on this LSA in topology Base with MTID 0

LS age: 253

Options: (No TOS-capability, DC, Upward)

LS Type: AS External Link

Link State ID: 10.2.0.0 (External Network Number )

Advertising Router: 172.16.1.4

LS Seq Number: 80000001

Checksum: 0xE134

Length: 36

Network Mask: /22

Metric Type: 2 (Larger than any link state path)

MTID: 0

Metric: 20

Forward Address: 172.16.1.2

External Route Tag: 0

//转发地址在nssa区域注入进来的外部路由中有重要意义,标识出了真实的ASBR究竟在哪里 //

Totally NSSA:

R1(config)#router ospf 110

R1(config-router)#area 2 nssa no-summary

R4(config)#router ospf 110

R4(config-router)#area 2 nssa no-summary

验证:

R2#show ip route ospf | begin Gateway

Gateway of last resort is 10.1.124.4 to network 0.0.0.0

O*IA 0.0.0.0/0 [110/11] via 10.1.124.4, 00:00:22, Ethernet0/2

[110/11] via 10.1.124.1, 00:00:39, Ethernet0/2

10.0.0.0/8 is variably subnetted, 11 subnets, 3 masks

O 10.2.0.0/22 is a summary, 00:09:16, Null0

R2#show ip ospf database database-summary

OSPF Router with ID (172.16.1.2) (Process ID 110)

Area 2 database summary

LSA Type Count Delete Maxage

Router 3 0 0

Network 1 0 0

Summary Net 2 0 0

Summary ASBR 0 0 0

Type-7 Ext 1 0 0

Prefixes redistributed in Type-7 1

Opaque Link 0 0 0

Opaque Area 0 0 0

Subtotal 7 0 0

Process 110 database summary

LSA Type Count Delete Maxage

Router 3 0 0

Network 1 0 0

Summary Net 2 0 0

Summary ASBR 0 0 0

Type-7 Ext 1 0 0

Opaque Link 0 0 0

Opaque Area 0 0 0

Type-5 Ext 0 0 0

Prefixes redistributed in Type-5 0

Opaque AS 0 0 0

Non-self 5

Total 7 0 0

// R2作为Totally NSSA区域的区域内路由器,LSDB已经进行了必要的精简和瘦身 //

配置强制由R1执行7转5的动作

R1#show run | s r o

router ospf 110

area 2 nssa translate type7 always

R3#show ip ospf database | begin Type-5

Type-5 AS External Link States

Link ID ADV Router Age Seq# Checksum Tag

10.2.0.0 172.16.1.1 24 0x80000001 0x00F325 0

在R4上将环回口重分布进OSPF特殊区域2,不允许该路由信息进入骨干区域

R4(config)#interface loopback 1

R4(config-if)#ip address 10.4.1.1 255.255.255.255

R4(config)#router ospf 110

R4(config-router)#redistribute connected nssa-only subnets

验证:

R4#show ip ospf database nssa-external self-originate

OSPF Router with ID (172.16.1.4) (Process ID 110)

Type-7 AS External Link States (Area 2)

LS age: 16

Options: (No TOS-capability, No Type 7/5 translation, DC, Upward)

LS Type: AS External Link

Link State ID: 10.4.1.1 (External Network Number )

Advertising Router: 172.16.1.4

LS Seq Number: 80000001

Checksum: 0x527A

Length: 36

Network Mask: /32

Metric Type: 2 (Larger than any link state path)

MTID: 0

Metric: 20

Forward Address: 0.0.0.0

External Route Tag: 0

// 注意:红字标识,标识该LSA不允许被执行 七转五的操作 //

因此,除了区域2之外,其它区域均无法收到该外部路由;

在R2上向特殊区域2内注入默认路由,该默认路由仅仅允许在特殊区域2内存在

R2(config-router)#area 2 nssa default-information-originate nssa-only

// 注意,该命令与参数仅仅在本地已经有一条默认路由的情况下才生效,能够在本地LADB中形成一条七类LSA,内容为默认路由;

R2#show ip ospf database nssa-external 0.0.0.0

OSPF Router with ID (172.16.1.2) (Process ID 110)

Type-7 AS External Link States (Area 2)

LS age: 71

Options: (No TOS-capability, No Type 7/5 translation, DC, Upward)

LS Type: AS External Link

Link State ID: 0.0.0.0 (External Network Number )

Advertising Router: 172.16.1.2

LS Seq Number: 80000001

Checksum: 0xBC75

Length: 36

Network Mask: /0

Metric Type: 2 (Larger than any link state path)

MTID: 0

Metric: 1

Forward Address: 172.16.1.2

External Route Tag: 0

一旦特殊区域与骨干区域失联,则会失去ABR,这时本区域的所有设备即可通过这条备用的默认路由出去;



谢谢大家!