So welcome back, guys.
Now we enter into the part two of this section.
In this section, we will going to understand deeply regarding how Layer three routing table construction
is done by a layer three device in the topology.
So take away from this section of the course is that you were going to learn how physical topology is
assimilated as graph data structure in local memory of each L3 routing device of a topology.
I explained about this briefly in the previous section.
In this section we will going to discuss in detail regarding what are the steps followed in order to
represent a physical topology as a graph data structure in the local memory of each router present in
the topology.
Then we will discuss the algorithm which is used to construct the routing table.
Needless to say that this algorithm applies on this input graph data structure which has already been
built into the local memory of a layer three router.
The algorithm that we will going to discuss is used by interior gateway routing protocols such as OSPF
or Is-Is.
Right.
And then once we learn the algorithm, then we will discuss the steps regarding how a router computes
its final routing table.
And this routing table constructed by the router will follow all the properties of a typical routing
table, such as ICMP loop free and shortest path.
So going forward.
So let us break down the problem into phases.
In the Phase one, we will discuss how input graph is built into the local memory of each layer three
device of the topology.
Right.
In the phase two, we will going to discuss the shortest path algorithm, famously known as Dijkstra's
algorithm and how this algorithm is applied on the input graph which is built in the phase one.
You must have already come across this algorithm in your academics, so you must revise this Dijkstra
algorithm and refer to your standard book.
Nevertheless, I will going to discuss how this shortest path first algorithm is slightly molded so
that it fits into the networking domain.
But you should refer to your standard book first in order to revise the fundamentals of Dijkstra algorithm.
And finally, in the Phase three, we will going to discuss the steps involved regarding how a L3 device
computes its final routing table from the raw output produced by the Dijkstra algorithm.
Right?
So you can see that all these three phases are connected.
The output of the phase one is used by the phase two, and the output of the phase two is used by the
phase three to produce the final output, which is routing table.
And I'm reiterating once again that this routing table will have the properties such as ICMP loop free,
and every destination should be reachable via shortest path in the topology.
So now in the remaining portion of this section, we will going to discuss each of these phases one
by one in pretty much detail.