Your task is to configure the following:
Portland's S0/0 interface in Area 1
Amani's S0/1 interface in Area 1
Use the appropriate mask such that ONLY Portland's S0/0 and Amnani's S0/1 could be in Area 1.
Area 1 should not receive any external or inter-area routes (except the default route).
First, we configure Portland's S0/0 interface so that it belongs to Area 1. So, we have to find out which sub-network the IP address 192.168.4.5/30 (the IP of interface S0/0 of Portland) belongs to. This address belongs to a subnetwork which has:
Increment: 4 (/30 = 255.255.255.252 or 1111 1111.1111 1111.1111 1111.1111 1100)
The question also requires that "Area 1 should not receive any external or inter-area routes (except the default route)". Recall that if we don't want the router to receive external routes, we have to stop LSA Type 5. And if we don't want to receive inter-area routes, we have to stop LSA Type 3 and Type 4. Therefore we have to configure area 1 as a totally stubby area. For your information, here is the definition of a totally stubby area:
"Totally stubb area - This area does not accept summary LSAs from other areas (types 3 or 4) or external summary LSAs (Type 5). Types 3,4 and 5 LSAs are replaced by the Area Border Router(ABR) with a default router. Totally stubby areas protect internal routers by minimizing the routing table and summarizing everything outside the area with a default route." (CCNP BSCI Official Exam Certification Guide, Fourth Edition)
In conclusion, we have to configure area 1 as a totally stubby area. We do that by configuring Portland as stub and configuring Amani (ABR router) as a stub + "no-summary"suffix.
+ Configure Portland router as a stub:
Portland#configure terminal
Portland(config)#router ospf 1
Allow network 192.168.4.4/30 to join Area 1, notice that you have to convert subnet mask into wildcard mask:
Portland(config-router)#network 192.168.4.4 0.0.0.3 area 1
Configure Portland as a stub:
Portland(config-router)#area 1 stub
Portland(config-router)#end
Portland#copy running-config startup-config
+ Configure Amani router as a "totally stub":
Amani#configure terminal
Amani(config)#router ospf 1
Amani(config-router)#network 192.168.4.4 0.0.0.3 area 1
Make area 1 become a totally stubby area, notice that we can only use this command on ABR router:
Amani(config-router)#area 1 stub no-summary
Amani(config-router)#end
Amani#copy running-config startup-config
Using GNS3 to simulate this OSPF lab:
Attached file: BSCI_Pass4sure_040_OSPF.rar
After configure the Area 1 is a totally stubby area, show routes on Portland router is as following:
Portland#show ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
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 192.168.4.6 to network 0.0.0.0
172.30.0.0/24 is subnetted, 1 subnets
C 172.30.49.0 is directly connected, Loopback1
192.168.4.0/30 is subnetted, 1 subnets
C 192.168.4.4 is directly connected, Serial0/0
O*IA 0.0.0.0/0 [110/65] via 192.168.4.6, 00:03:25, Serial0/0
