Lab 17 - OSPF NSSA Totally Stub Area

Prerequisites: CCNP level skills.

Note!
Use topology Lab14. OSPF should be enabled on all interfaces with the most specific wildcard mask.

Topology

Pic. 1 - OSPF Multi-Area Topology.

Icons designed by: Andrzej Szoblik - http://www.newo.pl

Task List

Task 1
On R1 create a new loopback interface with the IP address 192.168.1.1/24. Advertise this network in OSPF as external prefix. Make sure that no other interfaces created in the future will get advertised.

Task 2
On R5 create a new loopback interface with IP address 192.168.5.5/24. Advertise this network as external E2 into OSPF domain. 

Task 3
Configure routers in the area 1 so they do not accept any external and inter-area prefixes. Routers in area 1 must be able to reach the newly created networks. Routers in area 2 should be able to reach these networks as well.

Lab Solution

Task 1

On R1 create a new loopback interface with the IP address 192.168.1.1/24. Advertise this network in OSPF. Make sure that no other interfaces created in the future will get advertised.

R1 Configuration:

!
interface Loopback1
 ip address 192.168.1.1 255.255.255.0
!

route-map CONNECTED permit 10
 match interface Loopback1
!
router ospf 1
 router-id 1.1.1.1
 log-adjacency-changes
 redistribute connected subnets route-map CONNECTED
 network 10.1.12.1 0.0.0.0 area 0
 network 10.1.13.1 0.0.0.0 area 1
 network 172.16.101.1 0.0.0.0 area 0

!

Verification:

Pic. 2 - R2 Receives External E2 Prefix.

Task 2
On R5 create a new loopback interface with IP address 192.168.5.5/24. Advertise this network as external E2 into OSPF domain.

R5 Configuration:

!

interface Loopback1
 ip address 192.168.5.5 255.255.255.0

!

router ospf 1
 router-id 5.5.5.5
 log-adjacency-changes
 redistribute connected subnets
 network 10.1.35.5 0.0.0.0 area 1
 network 172.16.105.5 0.0.0.0 area 1

!

Verification:

Pic. 3 - R6 Receives External E2 Prefixes.

Task 3

Configure routers in area 1 so they do not accept any external and inter-area prefixes. Routers in area 1 must be able to reach the newly created networks. Routers in area 2 should be able to reach these networks as well.

Note!
Area 1 must filter LSA5 but also introduces external prefixes (192.168.5.0/24, 192.168.5.0/24). Area 1 CANNOT be configured as totally stubby area then. NSSA totally stub area is the solution. ABR will inject a default route into area that is NSSA totally stubby area (default behavior).

R1 Configuration:

!

router ospf 1
 router-id 1.1.1.1
 log-adjacency-changes
 area 1 nssa no-summary
 redistribute connected subnets route-map CONNECTED
 network 10.1.12.1 0.0.0.0 area 0
 network 10.1.13.1 0.0.0.0 area 1
 network 172.16.101.1 0.0.0.0 area 0

!

R3 Configuration:

!

router ospf 1
 router-id 3.3.3.3
 log-adjacency-changes
 area 1 nssa
 network 0.0.0.0 255.255.255.255 area 1

!

R5 Configuration:

!

router ospf 1
 router-id 5.5.5.5
 log-adjacency-changes
 area 1 nssa
 redistribute connected subnets
 network 10.1.35.5 0.0.0.0 area 1
 network 172.16.105.5 0.0.0.0 area 1

!

Verification:

Pic. 4 - R5's Routing Table.

External and Inter-Area prefixes are gone (no E2 or 0 IA).

Pic. 5 - R3's Routing Table.

Pic. 6 - R1's Routing Table.

Final ping tests.

Pic. 7 - Ping Between R5 and R1 NSSA Prefixes.

Pic. 8 - R6's Routing Table.

Both prefixes show as LSA5 in the area 2.

Pic. 9 - R6 Pings Both Networks.