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Totally STUB

Let’s continue from where we left off in Stub areas, now we will move ahead with TOTALLY STUB Area, as we know by now in totally stub area LSA3, 4, 5 all are blocked , lets verify the same by configuring the same topology as below.

To verify the same, we have configured Area 1 as totally stub area, external routing domain for type 4,5,7 LSA’s.

Lets dig into the lab section:

We are using the same topology throughout for all Stub area articles for simplication.

We will now configure area 1 as totally stub area and see the behaviour.

Let’s see how the routing table, OSPF database looks like before making area 1 as totally Stub area.

1#show ip route ospf 
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
       a - application route
       + - replicated route, % - next hop override

Gateway of last resort is not set

      20.0.0.0/24 is subnetted, 1 subnets
O E2     20.20.20.0 [110/20] via 192.168.12.2, 00:00:12, Ethernet0/0
      21.0.0.0/24 is subnetted, 1 subnets
O E2     21.21.21.0 [110/20] via 192.168.12.2, 00:00:12, Ethernet0/0
      22.0.0.0/24 is subnetted, 1 subnets
O E2     22.22.22.0 [110/20] via 192.168.12.2, 00:00:12, Ethernet0/0
      23.0.0.0/24 is subnetted, 1 subnets
O E2     23.23.23.0 [110/20] via 192.168.12.2, 00:00:12, Ethernet0/0
      40.0.0.0/24 is subnetted, 1 subnets
O E2     40.40.40.0 [110/20] via 192.168.12.2, 00:00:12, Ethernet0/0
      41.0.0.0/24 is subnetted, 1 subnets
O E2     41.41.41.0 [110/20] via 192.168.12.2, 00:00:12, Ethernet0/0
      42.0.0.0/24 is subnetted, 1 subnets
O E2     42.42.42.0 [110/20] via 192.168.12.2, 00:00:12, Ethernet0/0
      43.0.0.0/24 is subnetted, 1 subnets
O E2     43.43.43.0 [110/20] via 192.168.12.2, 00:00:12, Ethernet0/0
O IA  192.168.23.0/24 [110/20] via 192.168.12.2, 00:00:22, Ethernet0/0
O IA  192.168.34.0/24 [110/30] via 192.168.12.2, 00:00:22, Ethernet0/0
R1#

R1#show ip ospf database 

            OSPF Router with ID (13.13.13.13) (Process ID 1)

                Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
13.13.13.13     13.13.13.13     66          0x80000014 0x00744A 1
23.23.23.23     23.23.23.23     65          0x80000012 0x008EDF 1

                Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
192.168.12.2    23.23.23.23     65          0x8000000F 0x0022A5

                Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
192.168.23.0    23.23.23.23     70          0x8000000A 0x0077D5
192.168.34.0    23.23.23.23     70          0x8000000A 0x0062D5

                Summary ASB Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
43.43.43.43     23.23.23.23     70          0x80000001 0x00CD51

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
1.1.1.0         13.13.13.13     71          0x80000001 0x003C2D 0
5.0.0.0         13.13.13.13     71          0x80000001 0x001F48 0
10.10.10.0      13.13.13.13     71          0x80000001 0x00F657 0
11.11.11.0      13.13.13.13     71          0x80000001 0x00D278 0
12.12.12.0      13.13.13.13     71          0x80000001 0x00AE99 0
13.13.13.0      13.13.13.13     71          0x80000001 0x008ABA 0
20.20.20.0      23.23.23.23     1409        0x80000002 0x005EA8 0
21.21.21.0      23.23.23.23     1409        0x80000002 0x003AC9 0
22.22.22.0      23.23.23.23     1409        0x80000002 0x0016EA 0
23.23.23.0      23.23.23.23     1409        0x80000002 0x00F10C 0
40.40.40.0      43.43.43.43     1279        0x80000002 0x003149 0
41.41.41.0      43.43.43.43     1279        0x80000002 0x000D6A 0
42.42.42.0      43.43.43.43     1279        0x80000002 0x00E88B 0
43.43.43.0      43.43.43.43     1279        0x80000002 0x00C4AC 0
51.51.51.0      13.13.13.13     71          0x80000001 0x002DA5 0
R1#

As we see from the above output, LSA 3, 4, 5 are all present, and inter area and external routes traverse into area 1.

Now let’s making area 1 as stub and see how the router behaves.

R1(config)#router ospf 1
R1(config-router)#
R1(config-router)#area 1 stub
R1(config-router)#area 1 stub ?
  no-ext-capability  Do not send domain specific capabilities into stub area
  no-summary         Do not send summary LSA into stub area
  <cr>

R1(config-router)#area 1 stub no 
R1(config-router)#area 1 stub no-su
R1(config-router)#area 1 stub no-summary 
R1(config-router)#
*Jan 17 08:55:15.223: %OSPF-4-ASBR_WITHOUT_VALID_AREA: Router is currently an ASBR while having only one area which is a stub area
R1(config-router)#
*Jan 17 08:55:15.227: %OSPF-5-ADJCHG: Process 1, Nbr 23.23.23.23 on Ethernet0/0 from FULL to DOWN, Neighbor Down: Adjacency forced to reset
R1(config-router)#
*Jan 17 08:55:24.742: %OSPF-5-ADJCHG: Process 1, Nbr 23.23.23.23 on Ethernet0/0 from LOADING to FULL, Loading Done
R1(config-router)#

As you can see as soon i make area 1 as totally stub area, neighborship goes down and comes up, both routers in area 1 should match the same stub areas, lets check the database and route table now, LSA 3, 4, 5 should be gone now.

R1#
R1#show ip
*Jan 17 08:57:15.958: %SYS-5-CONFIG_I: Configured from console by console
R1#show ip route ospf
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
       a - application route
       + - replicated route, % - next hop override

Gateway of last resort is 192.168.12.2 to network 0.0.0.0

O*IA  0.0.0.0/0 [110/11] via 192.168.12.2, 00:01:46, Ethernet0/0
R1#
R1#

R1#show ip ospf da
R1#show ip ospf database 

            OSPF Router with ID (13.13.13.13) (Process ID 1)

                Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
13.13.13.13     13.13.13.13     128         0x80000016 0x008838 1
23.23.23.23     23.23.23.23     126         0x80000014 0x00A2CD 1

                Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
192.168.12.2    23.23.23.23     126         0x80000011 0x003C8B

                Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         23.23.23.23     131         0x80000001 0x00FCE4
R1#

As you can see there is no external LSA, not even LSA3 ( it just default), nor LSA 4 ( Summary LSA). also routing table shows only default entry which is given by ABR (R2), so it verifies our theory, Totally STUB area blocks LSA3, 4, 5.

I hope this has been informative to you and seen you in the next article !!!

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