OSPF ABR Type 3 LSA Filtering on Cisco IOS

Hello Helen.

I am assuming that you and the ISP are operating completely separate OSPF domains. That is, their OSPF routing is completely autonomous from yours. This means that your area 0 has nothing to do with their area 0. They are two completely separate systems.

If this is the case, then the way one OSPF domain communicates with another OSPF domain is via a router that has two separate OSPF processes running. One interface is using process number 1 for example, this may be your internal OSPF domain, and the outside interface is using process 2, which is part of the ISP’s OSPF domain. This is assuming that the redistribution point is your edge router. You can find detailed information of redistribution between separate OSPF domains at this comprehensive Cisco documentation.

Now if the ISP is participating in the SAME OSPF domain as you (which I consider unlikely, but I’m including this for completion), then there is essentially no redistribution taking place as far as domain to domain is concerned. Both are in the same domain.

I hope this has been helpful!

Laz

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