I briefly wrote about OSPF previously. As we saw OSPF packets are encapsulated in the IP Packets with protocol number 89. But how does OSPF establishes adjacency and how does it exchanges the Database? The process is part of another post. But before we go into those details, we must first know how the OSPF packets look like. This will give us an insight of what information they carry and later we can put all these pieces together and get to know when and why each of these packet contents are used?

So first what are the various types…

Lets jump into OSPF today and get to know few basics. OSPF stands for Open Shortest Path First. It is classified under IGP group of protocols. It is an example of a link-state routing protocol. Specifically the name of the algorithm used in OSPF is Dijkstra’s Algorithm. We will talk about it in a later post. The major way of functioning of a Link State Protocol (and hence OSPF), is exchanging the topology information using the “link states”. The link state implies that we include information about the link as well as the current state of the link. All the link states together form the Link State Database (LSDB).

Let me point out the steps into enabling and running OSPF in a network: