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:
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 subnetsR2(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 1R3(config)#router ospf 1
R3(config-router)#network 192.168.23.0 0.0.0.255 area 1All 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:
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.
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
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.
Hello Po
First of all, all four stub area types (Stub, Totally stub, NSSA, and totally NSSA) are characterized by the fact that they only have a single ABR. Remember, an ABR is an OSPF router that has two or more areas connected to it. This essentially means that there is only one entry and exit point from that particular area. This also means that area 0 can never be a stub network, because it is the backbone network to which all stubs connect. Remember that all ABRs must have at least one interface in area 0 for OSPF to function correctly. For a refreshe
... Continue reading in our forumThank you very much for your detailed explanation!