OSPF NSSA area configuration example

As shown in Figure 28:

• Configure OSPF on all switches and split AS into three areas.

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

• Configure Area 1 as an NSSA area and configure Switch C as an ASBR to redistribute static routes into the AS.

1. Configure IP addresses for interfaces.

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

3. Configure Area 1 as an NSSA area:

   # Configure Switch A.

   <SwitchA> system-view
   [SwitchA] ospf
   [SwitchA-ospf-1] area 1
   [SwitchA-ospf-1-area-0.0.0.1] nssa
   [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] nssa
   [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
    10.2.1.0/24        3        Transit 10.2.1.2        10.4.1.1        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: 5
    Intra area: 2  Inter area: 3  ASE: 0  NSSA: 0
   

4. Configure route redistribution:

   # Configure Switch C to redistribute static routes.

   [SwitchC] ip route-static 3.1.3.1 24 10.4.1.2
   [SwitchC] ospf
   [SwitchC-ospf-1] import-route static
   [SwitchC-ospf-1] quit
   

   # Display OSPF routing information on Switch D.

   <SwitchD> display ospf routing
   
             OSPF Process 1 with Router ID 10.5.1.1
                      Routing Table
   
                   Topology base (MTID 0)
   
    Routing for network
    Destination        Cost     Type    NextHop         AdvRouter       Area
    10.2.1.0/24        22       Inter   10.3.1.1        10.3.1.1        0.0.0.2
    10.3.1.0/24        10       Transit 10.3.1.2        10.3.1.1        0.0.0.2
    10.4.1.0/24        25       Inter   10.3.1.1        10.3.1.1        0.0.0.2
    10.5.1.0/24        10       Stub    10.5.1.1        10.5.1.1        0.0.0.2
    10.1.1.0/24        12       Inter   10.3.1.1        10.3.1.1        0.0.0.2
   
    Routing for ASEs
    Destination        Cost     Type    Tag         NextHop         AdvRouter
    3.1.3.0/24         1        Type2   1           10.3.1.1        10.2.1.1
   
    Total nets: 6
    Intra area: 2  Inter area: 3  ASE: 1  NSSA: 0
   

   The output shows that an external route imported from the NSSA area exists on Switch D.