LAB: OSPF NSSA ABR External Filtering

- Disable R6’s link to VLAN 146 and Loopback0.
- Configure area 2 as an NSSA.
- Configure summarization on R3 so that devices outside of area 2 do not have a route to the network 200.0.0.0/24.
- This filter should not affect any other prefixes.

commands:

R3:
router ospf 1
area 2 nssa

R6:
interface FastEthernet0/0.146
shutdown
!
interface Loopback0
shutdown
!
router ospf 1
area 2 nssa

SW1:
router ospf 1
area 2 nssa

SW3:
router ospf 1
area 2 nssa

summary address can be used to suppress the origination of Type-5 External LSA into Area0, the key difference of this from distribute-list and administrative distance filters is that the prefix is also filtered out in the ospf database not just the routing table.

before the summary-address filters is applied at R3.

Rack1R5#show ip ospf database external 200.0.0.0

            OSPF Router with ID (150.1.5.5) (Process ID 1)

                Type-5 AS External Link States

  Routing Bit Set on this LSA
  LS age: 16
  Options: (No TOS-capability, DC)
  LS Type: AS External Link
  Link State ID: 200.0.0.0 (External Network Number )
  Advertising Router: 150.1.3.3
  LS Seq Number: 80000001
  Checksum: 0x3BFE
  Length: 36
  Network Mask: /24
        Metric Type: 2 (Larger than any link state path)
        TOS: 0
        Metric: 20
        Forward Address: 0.0.0.0
        External Route Tag: 0

  LS age: 627
  Options: (No TOS-capability, DC)
  LS Type: AS External Link
  Link State ID: 200.0.0.0 (External Network Number )
  Advertising Router: 150.1.6.6
  LS Seq Number: 80000005
  Checksum: 0xC24
  Length: 36
  Network Mask: /24
        Metric Type: 2 (Larger than any link state path)
        TOS: 0
        Metric: 20
        Forward Address: 0.0.0.0
        External Route Tag: 0

Rack1R5#
Rack1R5#
Rack1R5#sho ip route | inc E2                  
       E1 - OSPF external type 1, E2 - OSPF external type 2
O E2    51.51.51.51 [110/20] via 155.1.0.2, 00:03:31, Serial0/0
O E2 204.12.1.0/24 [110/20] via 155.1.45.4, 00:03:31, Serial0/1
O E2 200.0.0.0/24 [110/20] via 155.1.0.3, 00:00:19, Serial0/0
O E2    54.1.1.0 [110/20] via 155.1.0.3, 00:03:31, Serial0/0
O E2 200.0.1.0/24 [110/20] via 155.1.0.3, 00:03:31, Serial0/0
O E2 200.0.2.0/24 [110/20] via 155.1.0.3, 00:03:31, Serial0/0
O E2 200.0.3.0/24 [110/20] via 155.1.0.3, 00:03:31, Serial0/0
O E2    9.9.9.9 [110/20] via 155.1.0.3, 00:03:30, Serial0/0
O E2    31.3.0.0 [110/20] via 155.1.45.4, 00:03:31, Serial0/1
O E2    31.2.0.0 [110/20] via 155.1.45.4, 00:03:31, Serial0/1
O E2    31.1.0.0 [110/20] via 155.1.45.4, 00:03:31, Serial0/1
O E2    31.0.0.0 [110/20] via 155.1.45.4, 00:03:31, Serial0/1
O E2    30.2.0.0 [110/20] via 155.1.45.4, 00:03:31, Serial0/1
O E2    30.3.0.0 [110/20] via 155.1.45.4, 00:03:31, Serial0/1
O E2    30.0.0.0 [110/20] via 155.1.45.4, 00:03:31, Serial0/1
O E2    30.1.0.0 [110/20] via 155.1.45.4, 00:03:31, Serial0/1

applying the summary-address filter at R3.

Rack1R3(config)#router ospf 1
Rack1R3(config-router)#summary-address 200.0.0.0 255.255.255.0 not-advertise

 verification:

 Rack1R5#show ip ospf database external 200.0.0.0

            OSPF Router with ID (150.1.5.5) (Process ID 1)

       
Rack1R5#sho ip route | inc E2                 
       E1 - OSPF external type 1, E2 - OSPF external type 2
O E2    51.51.51.51 [110/20] via 155.1.0.2, 00:01:33, Serial0/0
O E2 204.12.1.0/24 [110/20] via 155.1.45.4, 00:01:33, Serial0/1
O E2    54.1.1.0 [110/20] via 155.1.0.3, 00:01:33, Serial0/0
O E2 200.0.1.0/24 [110/20] via 155.1.0.3, 00:01:33, Serial0/0
O E2 200.0.2.0/24 [110/20] via 155.1.0.3, 00:01:33, Serial0/0
O E2 200.0.3.0/24 [110/20] via 155.1.0.3, 00:01:33, Serial0/0
O E2    9.9.9.9 [110/20] via 155.1.0.3, 00:01:33, Serial0/0
O E2    31.3.0.0 [110/20] via 155.1.45.4, 00:01:33, Serial0/1
O E2    31.2.0.0 [110/20] via 155.1.45.4, 00:01:33, Serial0/1
O E2    31.1.0.0 [110/20] via 155.1.45.4, 00:01:33, Serial0/1
O E2    31.0.0.0 [110/20] via 155.1.45.4, 00:01:33, Serial0/1
O E2    30.2.0.0 [110/20] via 155.1.45.4, 00:01:33, Serial0/1
O E2    30.3.0.0 [110/20] via 155.1.45.4, 00:01:33, Serial0/1
O E2    30.0.0.0 [110/20] via 155.1.45.4, 00:01:33, Serial0/1
O E2    30.1.0.0 [110/20] via 155.1.45.4, 00:01:33, Serial0/1