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Totally NSSA

Last but not the least Totally NSSA, it is exactly same as Totally Stub area, just type 7 LSA is allowed here.

Totally NSSA will block 3,4,5 but will allow type 7, ABR will convert this type 7 LSA to type LSA5 exactly the same way which we discussed in NSSA with capture by flipping P bit ( N or NSSA bit ).

Also we don’t need to manually give default route for reaching external routes which was the case in NSSA.

Lets check the behavior of Totally NSSA area.

Configuration is same just we add no-summary to NSSA config.

R1(config)#router ospf 1
R1(config-router)#area 1 stub
R1(config-router)#area 1 nssa no
R1(config-router)#area 1 nssa no-su
R1(config-router)#area 1 nssa no-summary 
R1(config-router)#
*Jan 17 10:11:23.037: %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 10:11:39.247: %OSPF-5-ADJCHG: Process 1, Nbr 23.23.23.23 on Ethernet0/0 from LOADING to FULL, Loading Done
R1(config-router)#

Let’s check the database, routing tables before and making Totally NSSA.

Before making Area 1 as Totally NSSA, we do have all the external routes in database as well routing table.

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 not set

      20.0.0.0/24 is subnetted, 1 subnets
O E2     20.20.20.0 [110/20] via 192.168.12.2, 00:00:10, Ethernet0/0
      21.0.0.0/24 is subnetted, 1 subnets
O E2     21.21.21.0 [110/20] via 192.168.12.2, 00:00:10, Ethernet0/0
      22.0.0.0/24 is subnetted, 1 subnets
O E2     22.22.22.0 [110/20] via 192.168.12.2, 00:00:10, Ethernet0/0
      23.0.0.0/24 is subnetted, 1 subnets
O E2     23.23.23.0 [110/20] via 192.168.12.2, 00:00:10, Ethernet0/0
      40.0.0.0/24 is subnetted, 1 subnets
O E2     40.40.40.0 [110/20] via 192.168.12.2, 00:00:10, Ethernet0/0
      41.0.0.0/24 is subnetted, 1 subnets
O E2     41.41.41.0 [110/20] via 192.168.12.2, 00:00:10, Ethernet0/0
      42.0.0.0/24 is subnetted, 1 subnets
O E2     42.42.42.0 [110/20] via 192.168.12.2, 00:00:10, Ethernet0/0
      43.0.0.0/24 is subnetted, 1 subnets
O E2     43.43.43.0 [110/20] via 192.168.12.2, 00:00:10, Ethernet0/0
O IA  192.168.23.0/24 [110/20] via 192.168.12.2, 00:00:10, Ethernet0/0
O IA  192.168.34.0/24 [110/30] via 192.168.12.2, 00:00:10, Ethernet0/0
R1#show ip ospf data
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     30          0x80000029 0x004A5F 1
23.23.23.23     23.23.23.23     27          0x80000025 0x0068F2 1

                Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
192.168.12.2    23.23.23.23     27          0x80000021 0x00FDB7

                Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
192.168.23.0    23.23.23.23     32          0x80000002 0x0087CD
192.168.34.0    23.23.23.23     32          0x80000002 0x0072CD

                Summary ASB Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
43.43.43.43     23.23.23.23     32          0x80000001 0x00CD51

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
1.1.1.0         13.13.13.13     35          0x80000001 0x003C2D 0
5.0.0.0         13.13.13.13     35          0x80000001 0x001F48 0
10.10.10.0      13.13.13.13     35          0x80000001 0x00F657 0
11.11.11.0      13.13.13.13     35          0x80000001 0x00D278 0
12.12.12.0      13.13.13.13     35          0x80000001 0x00AE99 0
13.13.13.0      13.13.13.13     35          0x80000001 0x008ABA 0
20.20.20.0      23.23.23.23     222         0x80000005 0x0058AB 0
21.21.21.0      23.23.23.23     222         0x80000005 0x0034CC 0
22.22.22.0      23.23.23.23     222         0x80000005 0x0010ED 0
23.23.23.0      23.23.23.23     222         0x80000005 0x00EB0F 0
40.40.40.0      43.43.43.43     470         0x80000005 0x002B4C 0
41.41.41.0      43.43.43.43     470         0x80000005 0x00076D 0
42.42.42.0      43.43.43.43     470         0x80000005 0x00E28E 0
43.43.43.0      43.43.43.43     470         0x80000005 0x00BEAF 0
51.51.51.0      13.13.13.13     35          0x80000001 0x002DA5 0
R1#

As you can see below, once we make Area 1 as totally NSSA, the O*E2 or the external routes are now seen as ON2 routes, also the default route is now injected into R1 by ABR.

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, 00:00:00, Ethernet0/0
      20.0.0.0/24 is subnetted, 1 subnets
O N2     20.20.20.0 [110/20] via 192.168.12.2, 00:00:00, Ethernet0/0
      21.0.0.0/24 is subnetted, 1 subnets
O N2     21.21.21.0 [110/20] via 192.168.12.2, 00:00:00, Ethernet0/0
      22.0.0.0/24 is subnetted, 1 subnets
O N2     22.22.22.0 [110/20] via 192.168.12.2, 00:00:00, Ethernet0/0
      23.0.0.0/24 is subnetted, 1 subnets
O N2     23.23.23.0 [110/20] via 192.168.12.2, 00:00:00, Ethernet0/0
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     15          0x8000002B 0x00EBB5 1
23.23.23.23     23.23.23.23     16          0x80000027 0x000A49 1

                Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
192.168.12.2    23.23.23.23     16          0x80000023 0x009F0E

                Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         23.23.23.23     22          0x80000001 0x008455

                Type-7 AS External Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Tag
1.1.1.0         13.13.13.13     26          0x80000001 0x008266 0
5.0.0.0         13.13.13.13     26          0x80000001 0x006581 0
10.10.10.0      13.13.13.13     26          0x80000001 0x003D90 0
11.11.11.0      13.13.13.13     26          0x80000001 0x0019B1 0
12.12.12.0      13.13.13.13     26          0x80000001 0x00F4D2 0
13.13.13.0      13.13.13.13     26          0x80000001 0x00D0F3 0
20.20.20.0      23.23.23.23     21          0x80000001 0x0044C1 0
21.21.21.0      23.23.23.23     21          0x80000001 0x0020E2 0
22.22.22.0      23.23.23.23     21          0x80000001 0x00FB04 0
23.23.23.0      23.23.23.23     21          0x80000001 0x00D725 0
51.51.51.0      13.13.13.13     26          0x80000001 0x0073DE 0
R1#

Rest all is same as NSSA, point to note here are

Only NSSA doesn’t inject default route, we need to manually give the default route in NSSA Stub area on ABR, rest all the types of Stub areas ABR injects the default route.

In, Totally NSSA area ABR does inject the default route, no manual intervention is needed.

ABR (R2) who knows the ASBR (R1) will do convert the Type 7 to Type 5 conversion and propagate further into ospf domain

ASBR (R1) will flip a pit bit ( N or NSSA) so that ABR ( R2) comes to know it has to do the conversion for this type 7 routes.

This is all about Totally Stub area, hope you like, stay tuned for more articles !!!!

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