So guys, now we will start with the discussion on how we can build the input graph that is phase one.
So you can see on the right hand side is a diagram which represents a physical network topology.
When I say a word physical, it simply means that the nodes of this diagram represents actual network
devices and they are connected via physical wires, right?
So it's a physical network topology.
So the phase one is all about building the input graph data structure in the local memory of each L3
device, which is running in this topology, Right?
So you can see that this particular cloud represents a data structures which exist in the local memory
of the device.
S And this data structure is nothing, but it is a representation of the actual physical network topology.
And we already know that network topology are best represented using graph data structures.
So the phase one involves four basic steps in the step one each routing device in the topology exchange
Hello packets.
By exchanging these hello packets, each routing device in the topology came to know about its neighbors.
For example, routing device A would know about neighbor B and neighbor S right.
Neighbors are those devices which are directly connected.
So by exchanging these hello packets, each device in the topology builds up its neighbor database.
A neighbor database is nothing, but it is just a database which contains information about neighbors.
Right?
In the Step three.
Once the L3 divides builds its neighbor database in its local memory.
Then it floods its Neighborship database so that every other device in the topology come to know that
who is neighbor of whom, Right?
So, for example, device device would know that C is the neighbor of D, Right.
And device S would also know that B is the neighbor of A right.
So flooding of the Neighborship database means that every device in the topology makes every other device
in the topology aware of its neighborship.
Right.
And then in final step number for each routing device in the topology builds up the cumulative Neighborship
database.
And this cumulative neighborship database is nothing, but it is the network graph data structure which
represents the actual physical topology.
Right?
So in the subsequent portion of this section, we will going to understand that how each of these steps
are accomplished as a part of phase one, building the input graph.
For now, I have just given you an overview regarding what we will going to deal in the next couple
of lecture videos.