Hour 40: OSPF an advanced link-state protocol

EIGRP is often called an advanced distance vector protocol because it has distance vector routing protocol AND link-state protocol properties. But wait a second… OSPF also has a mix of link-state and distance-vector protocol properties… So why is OSPF not called an “advanced link-state routing protocol”?

Let’s determine the properties of EIGRP that makes it an advanced distance protocol and then compare it to OSPF.

EIGRP distance-vector properties:

  • An EIGRP router only advertises its best route to its neighbor, not every route that it is aware of.
  • An EIGRP router does not have a complete map of the topology , it is only aware of what its neighbors have told it ( routing by rumor )

Now to prove that OSPF also has distance-vector properties, let’s look at OSPF’s Network Summary LSA (Type 3) characteristics:

In OSPF, when an ABR originates a Type 3 LSA and knows multiple paths to a destination, it will only advertise the lowest cost route into the backbone. When a router receives a Type 3 LSA from an ABR, it does not run the SPF algorithm. Rather, it simply adds the cost of the route to the ABR and the cost included in the LSA. Depending on another router instead of determining the full route to the destination is a distance-vector protocol behavior.

Now let’s compare these characteristics to the EIGRP distance-vector properties:

  • Type 3 LSA’s in an OSPF router only advertise its best route to the backbone, not every route that it is aware of.
  • Type 3 LSA’s in an OSPF router do not have a complete map of the topology, since it does not run the SPF algorithm. It is only aware of what the ABR originating the type 3 LSA told it.

These distance-vector properties are similar and we can conclude that OSPF also has distance-vector properties. By this logic, if we can call EIGRP an advanced distance vector protocol because it has link-state properties, can we then not also call OSPF an “advanced link-state protocol” since OSPF has distance vector properties?

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