OSPF stub area configuration example

As shown in Figure 27:

• Enable OSPF on all switches, and split the AS into three areas.

• Configure Switch A and Switch B as ABRs to forward routing information between areas.

• Configure Switch D as the ASBR to redistribute static routes.

• Configure Area 1 as a stub area to reduce advertised LSAs without influencing reachability.

1. Configure IP addresses for interfaces. (Details not shown.)

2. Enable OSPF (see "Basic OSPF configuration example").

3. Configure route redistribution:

   # Configure Switch D to redistribute static routes.

   <SwitchD> system-view
   [SwitchD] ip route-static 3.1.2.1 24 10.5.1.2
   [SwitchD] ospf
   [SwitchD-ospf-1] import-route static
   [SwitchD-ospf-1] quit
   

   # Display ABR/ASBR information on Switch C.

   <SwitchC> display ospf abr-asbr
   
             OSPF Process 1 with Router ID 10.4.1.1
                     Routing Table to ABR and ASBR
   
   
                   Topology base (MTID 0)
    Type        Destination     Area            Cost  Nexthop         RtType
    Intra       10.2.1.1        0.0.0.1         3     10.2.1.1        ABR
    Inter       10.5.1.1        0.0.0.1         7     10.2.1.1        ASBR
   

   # Display OSPF routing table on Switch C.

   <SwitchC> display ospf routing
   
             OSPF Process 1 with Router ID 10.4.1.1
                      Routing Table
   
                   Topology base (MTID 0)
   
    Routing for network
    Destination        Cost     Type    NextHop         AdvRouter       Area
    10.2.1.0/24        3        Transit 0.0.0.0         10.2.1.1        0.0.0.1
    10.3.1.0/24        7        Inter   10.2.1.1        10.2.1.1        0.0.0.1
    10.4.1.0/24        3        Stub    10.4.1.1        10.4.1.1        0.0.0.1
    10.5.1.0/24        17       Inter   10.2.1.1        10.2.1.1        0.0.0.1
    10.1.1.0/24        5        Inter   10.2.1.1        10.2.1.1        0.0.0.1
   
    Routing for ASEs
    Destination        Cost     Type    Tag         NextHop         AdvRouter
    3.1.2.0/24         1        Type2   1           10.2.1.1        10.5.1.1
   
    Total nets: 6
    Intra area: 2  Inter area: 3  ASE: 1  NSSA: 0
   

   The output shows that Switch C's routing table contains an AS external route.

4. Configure Area 1 as a stub area:

   # Configure Switch A.

   <SwitchA> system-view
   [SwitchA] ospf
   [SwitchA-ospf-1] area 1
   [SwitchA-ospf-1-area-0.0.0.1] stub
   [SwitchA-ospf-1-area-0.0.0.1] quit
   [SwitchA-ospf-1] quit
   

   # Configure Switch C.

   <SwitchC> system-view
   [SwitchC] ospf
   [SwitchC-ospf-1] area 1
   [SwitchC-ospf-1-area-0.0.0.1] stub
   [SwitchC-ospf-1-area-0.0.0.1] quit
   [SwitchC-ospf-1] quit
   

   # Display OSPF routing information on Switch C

   [SwitchC] display ospf routing
   
             OSPF Process 1 with Router ID 10.4.1.1
                      Routing Table
   
                   Topology base (MTID 0)
   
    Routing for network
    Destination        Cost     Type    NextHop         AdvRouter       Area
    0.0.0.0/0          4        Inter   10.2.1.1        10.2.1.1        0.0.0.1
    10.2.1.0/24        3        Transit 0.0.0.0         10.2.1.1        0.0.0.1
    10.3.1.0/24        7        Inter   10.2.1.1        10.2.1.1        0.0.0.1
    10.4.1.0/24        3        Stub    10.4.1.1        10.4.1.1        0.0.0.1
    10.5.1.0/24        17       Inter   10.2.1.1        10.2.1.1        0.0.0.1
    10.1.1.0/24        5        Inter   10.2.1.1        10.2.1.1        0.0.0.1
   
    Total nets: 6
    Intra area: 2  Inter area: 4  ASE: 0  NSSA: 0
   

   The output shows that a default route replaces the AS external route.

   # Configure Area 1 as a totally stub area.

   [SwitchA] ospf
   [SwitchA-ospf-1] area 1
   [SwitchA-ospf-1-area-0.0.0.1] stub no-summary
   [SwitchA-ospf-1-area-0.0.0.1] quit
   [SwitchA-ospf-1] quit
   

   # Display OSPF routing information on Switch C.

   [SwitchC] display ospf routing
   
             OSPF Process 1 with Router ID 10.4.1.1
                      Routing Table
   
                   Topology base (MTID 0)
   
    Routing for network
    Destination        Cost     Type    NextHop         AdvRouter       Area
    0.0.0.0/0          4        Inter   10.2.1.1        10.2.1.1        0.0.0.1
    10.2.1.0/24        3        Transit 0.0.0.0         10.4.1.1        0.0.0.1
    10.4.1.0/24        3        Stub    10.4.1.1        10.4.1.1        0.0.0.1
   
    Total nets: 3
    Intra area: 2  Inter area: 1  ASE: 0  NSSA: 0
   

   The output shows that inter-area routes are removed, and only one external route (a default route) exists on Switch C.