How to configure OSPF Totally Stub Area

In the first lesson I gave an overview of the different OSPF special area types. I also covered the OSPF stub area and now it’s time to demonstrate the totally stub area.  This is the network topology that we will use:

ospf stub area
Above you see two areas, 0 and 1. This is the configuration that we will use:

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

All the networks are advertised in the correct OSPF areas with the exception of the loopback0 interface on R1. We will redistribute it so it becomes a LSA type 5. Let’s take a look at the routing table of R3:

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Forum Replies

  1. Hi Rene,

    As I read some article about STUB, Stub-Summary, NSSA, NSSA-Summary. It just block External Route or Internal Route or Both to advertise, but it always inject default route to destination. the purpose the new these feature to reduce amount of cpu hit. Am i right ?

    Please explain more about it.

  2. Hi Palani,

    It does sound conflicting yes but that’s how it works. The default route is advertised as a LSA type 3 (summary LSA) in the totally stub area. All other summary LSAs are not permitted though.

    Rene

  3. Why exactly is the ABR the only one in a stub area to require the “no summary” keyword?
    I lab’d it up in GNS3 and your right the others dont need it to work and be a stub area, I was just curious as to why?
    Why dont the others in the stub area require “no summary”?
    Thanks

  4. Rafael,
    The difference between a Stub and a Totally Stubby Area occurs only at the ABR (the ABR determines what type of LSAs to allow into the Stub / Totally Stubby area). Since from the perspective of routers within the area there is no functional difference, there was no need to have extra information which might otherwise break the routers from forming a neighbor relationship.

  5. Rene,

    Got my response to the question which I posted in the stub area page.

    Love your work, as always…

    I have learned most of my topics by watching your gns3vault & now network lesson is to the next level.

    Kudos to you for all your efforts!

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