OSPF SUTB区域和Total STUB区域的默认路由

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
 area 1 stub

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
 area 1 stub

end

(1)解释在Stub Area 中的OSPF数据库
The ABR for the stub area originates a summary LSA with a link ID of 0.0.0.0. It does this even if it does not have a default route. You can see this happen with the show ip ospf database command.

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     19     0x80000001     0x8F8B         1

                Summary Net Link States (Area 0)

Link ID   ADV Router   Age     Seq#           Checksum
5.0.0.0    2.2.2.2     9       0x80000001     0x8E61

                Router Link States (Area 1)

Link ID   ADV Router   Age     Seq#           Checksum   Link count
1.1.1.1    1.1.1.1     1335    0x80000059     0x56DA         2
2.2.2.2    2.2.2.2     4       0x80000013     0x7FF3         2

                Summary Net Link States (Area 1)

Link ID   ADV Router   Age     Seq#               Checksum
0.0.0.0    2.2.2.2     20      0x80000001         0x75C0
6.0.0.0    2.2.2.2     13      0x80000001         0x2709

r2.2.2.2#show ip ospf database summary 0.0.0.0

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

                Summary Net Link States (Area 1)

  LS age: 184
  Options: (No TOS-capability, DC)
  LS Type: Summary Links(Network)
  Link State ID: 0.0.0.0 (summary Network Number)
 
!--- The ABR (Router 2.2.2.2) injects a default route
  !--- into the stub area.

  Advertising Router: 2.2.2.2
  LS Seq Number: 80000001
  Checksum: 0x75C0
  Length: 28
  Network Mask: /0
        TOS: 0  Metric: 1
 

r2.2.2.2#show ip route 0.0.0.0
% Network not in table

!--- The ABR (Router 2.2.2.2) does not have a default route
!--- in its routing table.

r1.1.1.1#show ip route ospf
O IA 6.0.0.0/8 [110/65] via 5.0.0.2, 00:04:23, Serial2/1/0
O*IA 0.0.0.0/0 [110/65] via 5.0.0.2, 00:04:23, Serial2/1/0

(2)解释在Totally Stub Area 中的OSPF数据库
If you change area 1 in the stub area example from a stub area to a totally stub area, the ABR still injects the 0.0.0.0 summary LSA into area 1. The only difference is that other summary LSAs are not sent into the totally stub area.

Note: The only configuration change made was to the ABR. The no-summary statement was added to its OSPF configuration: area 1 stub no-summary.

This command output shows what the OSPF database looks like in a totally stub area.

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     617     0x80000001   0x8F8B           1

                Summary Net Link States (Area 0)

Link ID   ADV Router   Age     Seq#         Checksum
5.0.0.0    2.2.2.2     608     0x80000001   0x8E61

                Summary ASB Link States (Area 0)

Link ID   ADV Router   Age     Seq#         Checksum
1.1.1.1    2.2.2.2     243     0x80000003   0x8F5E

                Router Link States (Area 1)

Link ID   ADV Router   Age     Seq#         Checksum     Link count
1.1.1.1    1.1.1.1     1934    0x80000059   0x56DA           2
2.2.2.2    2.2.2.2     247     0x80000015   0x7BF5           2

                Summary Net Link States (Area 1)

Link ID   ADV Router   Age     Seq#               Checksum
0.0.0.0    2.2.2.2     249     0x80000003         0x71C2 

!--- Notice that this is the only summary LSA
!--- in the totally stub area.

r1.1.1.1#show ip route ospf
O*IA 0.0.0.0/0 [110/65] via 5.0.0.2, 00:04:11, Serial2/1/0
The ABR does not originate a summary LSA for 6.0.0.0/8. As a result, Router 1.1.1.1 no longer has a route for 6.0.0.0/8. The only inter-area route this router has is the default route.