向OSPF区域注入一条默认路由

爱是王道

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