OSPF Stub Area Sim configuration on GNS3:

Question

A company has three  routers Protland, Amsni and Lynaic. OSPF is configured on routers Amani and Lynaic. Amani’s S0/0 interface and Lynaic’s S0/1 interface are in Area 0. Lynaic’s Loopback0 interface is in Area 2. Details of configuration are as follow:

Portland’s S1/0 interface in Area 1
Amani’s S1/0 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).

GNS3 Configurations:

First you need to create this topology in GNS3 as show above with following configurations.

Portland Router:

R1#config t

R1 (config)# hostname Portland

Portland (config)# enable secret cisco

Portland (config)#interface Serial1/0

Portland (config-if)# ip address 192.168.4.5 255.255.255.252

Portland (config-if)#no shutdown

Anami Router:

R2#config t

R2 (config)# hostname Anami

Anami (config)# enable secret cisco

Anami (config)#interface Serial1/0

Anami (config-if)# ip address 192.168.4.6 255.255.255.252

Anami (config-if)# no shutdown

Anami (config)#interface Serial1/1

Anami (config-if)# ip address 192.168.72.6 255.255.255.252

Anami (config-if)#no shutdown

Anami (config)#exit

Anami (config)#router ospf 1

Anami (config-router)# network 192.168.4.4 0.0.0.3 area 1

Anami (config-router)# network 192.168.72.4 0.0.0.3 area 0

Lynaic Router:

R3#config t

R3 (config)# hostname Lynaic

Lynaic (config)# enable secret cisco

Lynaic (config)#interface loopback 1

Lynaic (config-if)# ip address 239.239.239.239 255.255.255.255

Lynaic (config-if)# ex

Lynaic (config)#interface Serial1/0

Lynaic (config-if)# ip address 192.168.72.5 255.255.255.252

Lynaic (config-if)#no shutdown

Lynaic (config)#exit

Lynaic (config)#router ospf 1

Lynaic (config-router)# network 239.239.239.239 0.0.0.0 area 2

Lynaic (config-router)# network 192.168.72.4 0.0.0.3 area 0

Configuratio that you need  in real exam:

From above configuration you have notice that Portland router and Anami’s S1/0 interface is not running OSPF that way they are not able to communicate with other. In order to complete the configuration you need to run OSPF on these. For appropriate mask for 192.168.4.5\30 you need to find out the network ID for this subnet.

1	2	3	4	5	6	7	8
128	64	32	16	8	4	2	0

As we know that \30 is 6^th bit of 4^th octet that way from above table these subnets are divided into four number differences as follow.

Subet IDs for \30	Broadcast Address
0	3
4	7
8	11
12	15
And so on…….	……..

And from above we can see that 192.168.4.5 lie in 4-7 range therefore

Subnet ID=192.168.4.4

Portland#configure terminal
Portland(config)#router ospf 1

Portland(config-router)#network 192.168.4.4 0.0.0.3 area 1

“Area 1 should not receive any external or inter-area routes” configure area 1 as totally stubby area.

Portland(config-router)#area 1 stub

Portland(config-router)#end
Portland#copy running-config startup-config

Amani#configure terminal
Amani(config)#router ospf 1
Amani(config-router)#network 192.168.4.4 0.0.0.3 area 1

Amani(config-router)#area 1 stub no-summary

Testing:

Ping from Lynaic to Portland should be successful and Lynaic have all route in its routing table.

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