Network technologies and trends

Jan 24 2016   5:33AM GMT

How to configure Stub Area in OSPF – Series 2?

Yasir Irfan Yasir Irfan Profile: Yasir Irfan

Tags:
Cisco
Cisco IOS
Dynamic Routing
IP routing protocols
Loopback
OSPF
OSPF protocol
Routing

In my previous post we studied the topology and saw how Type 5 LSA routes are installed in non 0 Area. Now lets configure Area 5 as a stub area.

Its very easy to configure a stub area , by enabling the Cisco IOS Command  ” area X stub ” in OSPF process one can enable Stub area ,X is the area number.

In our case we need to configure Area 5 as a stub area by using the below Cisco IOS command in Routers R2 and R3

router ospf 1

area 5 stub

R2 Stub

 

 

R3 Stub

 

Now lets examine how R4 loopback interface networks are installed in R3 router

R3 -R4 Routes

We can see there are no specific routes for R4 loopback interfaces, networks 10.0.1.0 , 10.0.2.0, 10.0.3.0 and 10.0.4.0 are replaced by a default route.

We cannot see a specific route for the R4 Loopback interface 1 , its not in the routing table, however when we examine the CEF table we can discover the nexthop  for the network 10.0.1.0 is 192.168.23.3 which happens to be the R2 interface connecting to R3 and also there is a reachability.

R3 CEF

 

 

 

R3-R4 Reachability

 

 

 

By configuring a Stub Area one can install all the external routes ( type 5 LSAs) using a default route, the greatest advantage one could see is the size of routing table and OSPF database is reduced to a smaller size

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