向OSPF区域注入一条默认路由

Default routes injected into a normal area can be originated by any OSPF router. The OSPF router does not, by default, generate a default route into the OSPF domain. In order for OSPF to generate a default route, you must use the default-information originate command.

有两张方法向OSPF区域注入一条默认路由
(1) The first is to advertise 0.0.0.0 into the OSPF domain, provided the advertising router already has a default route.
(2)The second is to advertise 0.0.0.0 regardless of whether the advertising router already has a default route. The second method can be accomplished by adding the keyword always to the default-information originate command.

Router 1.1.1.1

Current configuration:

hostname r1.1.1.1

interface Loopback0
 ip address 1.1.1.1 255.0.0.0

interface Serial2/1/0
 ip address 5.0.0.1 255.0.0.0
 
router ospf 2
 network 5.0.0.0 0.255.255.255 area 1

end

Router 2.2.2.2

Current configuration:

hostname r2.2.2.2

interface Loopback0
 ip address 2.2.2.2 255.0.0.0
 
interface Serial0/1/0
 ip address 5.0.0.2 255.0.0.0

interface ATM1/0.20
 ip address 6.0.0.2 255.0.0.0
 
router ospf 2
 network 5.0.0.0 0.255.255.255 area 1
 network 6.0.0.0 0.255.255.255 area 0
 default-information originate
 
ip route 0.0.0.0 0.0.0.0 6.0.0.3

end

r2.2.2.2#show ip ospf database 

       OSPF Router with ID (2.2.2.2) (Process ID 2) 

                Router Link States (Area 0) 

Link ID   ADV Router   Age     Seq#          Checksum   Link count 
2.2.2.2    2.2.2.2     600     0x80000001    0x9583          1 

                Summary Net Link States (Area 0) 

Link ID    ADV Router   Age     Seq#          Checksum 
5.0.0.0     2.2.2.2     600     0x80000001    0x8E61 

                Router Link States (Area 1) 

Link ID   ADV Router   Age     Seq#           Checksum   Link count 
1.1.1.1    1.1.1.1     864     0x8000005E     0xD350         2 
2.2.2.2    2.2.2.2     584     0x8000001E     0xF667         2 

                Summary Net Link States (Area 1) 

Link ID   ADV Router   Age     Seq#          Checksum 
6.0.0.0    2.2.2.2     585     0x80000004    0xA87C 

                Type-5 AS External Link States 

Link ID   ADV Router   Age     Seq#          Checksum    Tag 
0.0.0.0    2.2.2.2     601     0x80000001    0xD0D8       0 

Because it has a default route, Router 2.2.2.2 originates a type 5 LSA with a link ID of 0.0.0.0. This is the result of the default-information originate command in its OSPF configuration.

r2.2.2.2#show ip ospf database external 0.0.0.0 

       OSPF Router with ID (2.2.2.2) (Process ID 2) 

                Type-5 AS External Link States  

  LS age: 650 
  Options: (No TOS-capability, DC) 
  LS Type: AS External Link 
  Link State ID: 0.0.0.0 (External Network Number ) 
  Advertising Router: 2.2.2.2 
  LS Seq Number: 80000001 
  Checksum: 0xD0D8 
  Length: 36 
  Network Mask: /0 
        Metric Type: 2 (Larger than any link state path) 
        TOS: 0 
        Metric: 1 
        Forward Address: 0.0.0.0 
        External Route Tag: 0 


r2.2.2.2#show ip route 0.0.0.0 
S* 0.0.0.0/0 [1/0] via 6.0.0.3, 00:28:00, ATM1/0.20  


r1.1.1.1#show ip route ospf 
O IA 6.0.0.0/8 [110/65] via 5.0.0.2, 00:00:18, Serial2/1/0 
O*E2 0.0.0.0/0 [110/1] via 5.0.0.2, 00:00:18, Serial2/1/0