How to configure OSPF Stub Area

Previously I explained the different OSPF special area types called “stub areas”. In the next series of lessons I will show you the configuration of each OSPF stub type. Let’s start with the “normal” stub type. This is the topology that we will use:

ospf stub area

In the picture above we have 2 areas…area 0 and area 1. I’ll use this topology to demonstrate all the OSPF area types to you. Let me show you the configuration:

R1(config)#router ospf 1
R1(config-router)#network 192.168.12.0 0.0.0.255 area 0
R1(config-router)#redistribute connected subnets
R2(config)#router ospf 1
R2(config-router)#network 192.168.12.0 0.0.0.255 area 0
R2(config-router)#network 192.168.23.0 0.0.0.255 area 1
R3(config)#router ospf 1
R3(config-router)#network 192.168.23.0 0.0.0.255 area 1

I advertised all the interfaces in the correct OSPF areas with the exception of the loopback0 interface on R1. This interface is redistributed into OSPF so it becomes a LSA Type 5.

R3#show ip route ospf 
O IA 192.168.12.0/24 [110/2] via 192.168.23.2, 00:08:53, FastEthernet0/0
     1.0.0.0/24 is subnetted, 1 subnets
O E2    1.1.1.0 [110/20] via 192.168.23.2, 00:01:16, FastEthernet0/0

When we look at R3 you’ll see network 192.168.12.0 /24 as inter-area (LSA Type 3) and 1.1.1.0 /24 as external type 2 (LSA Type 5). Now let’s change area 1 in a stub area:

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Forum Replies

  1. Udaya,
    A type-3 default route generated by an ABR into its directly attached totally stubby area is an exception to the no LSA type 3 rule. This is the only type-3 route allowed within an totally stubby area.

  2. Hello Yamini

    Rene’s lesson on types of stub areas very clearly indicates the functionality of each. You can find it here.

    However, I’ll try to give you a quick summary of why you would use each case in a real life scenario.

    A stub area would be configured if a network segment had only one choice for routing all traffic. An example of this would be a branch office that has only one gateway. There is no need for LSAs of type 5 to be advertised within this network since all routes will point to the local default gateway.

    A totally stubby area would be configure

    ... Continue reading in our forum

  3. Let me use another topology to explain where/why you could use stub areas:

    //cdn-forum.networklessons.com/uploads/default/original/1X/26cb0f0874dbfe65180eceffe6b3778afc22b1a1.png

    OSPF is our “campus” network. Area 0 is the main network, area 1,2, and 3 are branch offices. BGP routes are redistributed into OSPF, RIP routes are also redistributed into OSPF.

    With regular areas, all routers will learn about all prefixes out there. When you look at this picture…why would area 1, 2, or 3 need to know the prefixes from BGP? There is only one path, and that is through

    ... Continue reading in our forum

  4. ah don’t do that Rene you already are very responsive and take care of the website. Save your time for important stuff it was small inconvenience only I just glossed over the names and focused on specific granular that I was having problems with but makes

    ... Continue reading in our forum

  5. Hi Rene,
    That was mind blowing. Clear concept indeed . The stub/Totally Stub concerned to how many exit point from a area .The NSSA/Totally NSSA needed when ASBR needed on a area .Thx

    br//zaman

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