OSPF Areas: Totally Stubby Area:
· Totally stubby areas are areas into which external LSAs and summary LSAs are not flooded.
· The only route injected into the totally-stubby-area is the default-route by an ABR.
· **Intra-routes will be there as they are local to this area.
Network topology and Configs are same as the previous post (Stub Area).
· In the previous post, we have observed that, after configuring Area 1 as Stub area, External LSAs were blocked by an ABR to enter the Stub Area.
· But we still observed Inter-area routes. (Summary LSAs were still allowed)
Now, let me configure Area 1 as Totally Stubby Area:
R2(config)#router ospf 1
R2(config-router)#area 1 stub no-summary
R2(config-router)#
Now, if we see the Routing table of R3, we shouldn’t see External and Inter-area routes (LSA 5 and LSA 3). Let’s check that:
R3#show ip route
Codes: 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
Gateway of last resort is 20.1.1.2 to network 0.0.0.0
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
20.0.0.0/24 is subnetted, 1 subnets
C 20.1.1.0 is directly connected, Serial1/1
O*IA 0.0.0.0/0 [110/65] via 20.1.1.2, 00:01:53, Serial1/1
R3#
· We don’t see any External routes and Inter-area routes.
· We just see a default route injected by an ABR into TotallY Stbby Area.
· I haven’t configured any intra-routes, otherwise they should still be appearing
· To check this, let me create a new loopback on R2 and advertise it into Area1, so that we see it on R3.
R2(config)#int loop22
R2(config-if)#ip add
*Jun 15 14:10:21.947: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback22, changed state to up
R2(config-if)#ip add 22.22.22.22 255.255.255.255
R2(config-if)#router ospf 1
R2(config-router)#net 22.22.22.22 0.0.0.0 area 1
R2(config-router)#
Now, let’s check the R3’s Routing Table:
R3#show ip route
Codes: 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
Gateway of last resort is 20.1.1.2 to network 0.0.0.0
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
20.0.0.0/24 is subnetted, 1 subnets
C 20.1.1.0 is directly connected, Serial1/1
22.0.0.0/32 is subnetted, 1 subnets
O 22.22.22.22 [110/65] via 20.1.1.2, 00:00:55, Serial1/1
O*IA 0.0.0.0/0 [110/65] via 20.1.1.2, 00:00:55, Serial1/1
R3#
Yes, we see R2’ loopback as intra-area route!!!
We will learn about NSSA area in the next post à
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