Totally Stubby Area

In OSPF (Open Shortest Path First) for IPv4, a Totally Stubby Area is a special type of OSPF area that limits the information about external routes injected into the area. In a Totally Stubby Area, not only are external routes from other Autonomous Systems (ASes) summarized, but also Type 3 Summary LSAs are further limited, condensing the topology information within the OSPF domain. This design reduces the size of the routing tables within the Totally Stubby Area, promoting scalability and simplifying the routing decision-making process for routers within that area. The Area Border Router (ABR) at the boundary of the Totally Stubby Area injects a default route into the area, allowing routers within the area to reach destinations outside the OSPF domain efficiently. Totally Stubby Areas are particularly beneficial in large networks where efficient space utilization and reduced routing overhead are essential considerations.

Lab:

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Cisco IOS Software, Linux Software (I86BI_LINUX-ADVENTERPRISEK9-M), Version 15.2(4)M1, DEVELOPMENT TEST SOFTWARE

Task 1: Configure OSPF Totally Stubby Area

Step 1: In the configuration mode of router configure loopbacks with network address in sequence & redistribute these connected network in OSPF process

R2:
interface loopback 100
ip address 100.0.0.2 255.255.255.0
interface loopback 101
ip address 100.0.1.2 255.255.255.0
interface loopback 102
ip address 100.0.2.2 255.255.255.0
interface loopback 103
ip address 100.0.3.2 255.255.255.0
exit

R2:
router ospf 2
redistribute connected subnet metric-type 1
exit

R1#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - OSPF, EX - OSPF external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is not set

      11.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
C        11.0.0.0/24 is directly connected, Loopback0
L        11.0.0.1/32 is directly connected, Loopback0
C        11.0.1.0/24 is directly connected, Loopback1
L        11.0.1.1/32 is directly connected, Loopback1
C        11.0.2.0/24 is directly connected, Loopback2
L        11.0.2.1/32 is directly connected, Loopback2
C        11.0.3.0/24 is directly connected, Loopback3
L        11.0.3.1/32 is directly connected, Loopback3
      12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        12.0.0.0/24 is directly connected, Serial2/0
L        12.0.0.1/32 is directly connected, Serial2/0
      22.0.0.0/22 is subnetted, 1 subnets
O IA     22.0.0.0 [110/65] via 12.0.0.2, 00:33:04, Serial2/0
      23.0.0.0/24 is subnetted, 1 subnets
O IA     23.0.0.0 [110/74] via 12.0.0.2, 02:05:41, Serial2/0
      33.0.0.0/32 is subnetted, 3 subnets
O IA     33.0.1.3 [110/75] via 12.0.0.2, 02:05:41, Serial2/0
O IA     33.0.2.3 [110/75] via 12.0.0.2, 02:05:41, Serial2/0
O IA     33.0.3.3 [110/75] via 12.0.0.2, 02:05:41, Serial2/0
      34.0.0.0/24 is subnetted, 1 subnets
O IA     34.0.0.0 [110/138] via 12.0.0.2, 02:05:41, Serial2/0
      44.0.0.0/32 is subnetted, 3 subnets
O IA     44.0.1.4 [110/139] via 12.0.0.2, 02:05:41, Serial2/0
O IA     44.0.2.4 [110/139] via 12.0.0.2, 02:05:41, Serial2/0
O IA     44.0.3.4 [110/139] via 12.0.0.2, 02:05:41, Serial2/0
      100.0.0.0/24 is subnetted, 4 subnets
O E1     100.0.0.0 [110/84] via 12.0.0.2, 00:00:16, Serial2/0
O E1     100.0.1.0 [110/84] via 12.0.0.2, 00:00:16, Serial2/0
O E1     100.0.2.0 [110/84] via 12.0.0.2, 00:00:16, Serial2/0
O E1     100.0.3.0 [110/84] via 12.0.0.2, 00:00:16, Serial2/0

Step 2: Configure OSPF Stub

R2:
router ospf 2
area 1 stub no-summary
exit

R1:
router ospf 1
area 1 stub no-summary
exit

Task 2: Verification:

Step 1: Verify routes on neighbor router routing table

R1#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is 12.0.0.2 to network 0.0.0.0

O*IA  0.0.0.0/0 [110/65] via 12.0.0.2, 00:00:19, Serial2/0
            11.0.0.0/32 is subnetted, 3 subnets
C        11.0.0.0/24 is directly connected, Loopback0
L        11.0.0.1/32 is directly connected, Loopback0
C        11.0.1.0/24 is directly connected, Loopback1
L        11.0.1.1/32 is directly connected, Loopback1
C        11.0.2.0/24 is directly connected, Loopback2
L        11.0.2.1/32 is directly connected, Loopback2
C        11.0.3.0/24 is directly connected, Loopback3
L        11.0.3.1/32 is directly connected, Loopback3
      12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        12.0.0.0/24 is directly connected, Serial2/0
L        12.0.0.1/32 is directly connected, Serial2/0

Total Stubby area is area in which external routes LSA 5 and Inter-area routes LSA3/4 does not propagate, instead it automatically creates default route 0.0.0.0 towards ABR.

R1#ping 100.0.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 100.0.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/9 ms

R1#ping 22.0.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 22.0.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/9 ms