So guys, now we are done with the phase two of procedure of construction of layer three routing table.
Now, we entered into the phase three where we will eventually compute the final routing table.
So phase three uses the output of the phase two as an input for the construction or calculation of actual
routing table.
So, guys, on this slide, you can see that this is the output that is produced as a result of execution
of SPF algorithm on this input graph data structure by taking the source node as as the starting node.
So this table is the SPF result of the node as.
Now computation of the routing table from this raw table is just one step process.
You can see that the final routing table can be computed by simply replacing the destination node names
with their respective loopback address.
Right.
So it is just a matter of replacing the destination nodes with their respective addresses.
We will get the final routing table of the nodes.
So for the node AZ, in order to reach the following IP address, the outgoing interface is Ethernet
one that is this and the gateway IP address is 2.2.2.2 and outgoing interface and Gateway is the minimal
information which is required by the router to know how to forward the traffic.
The rest of the information for each entry in this routing table serves the purpose of only additional
information.
So with this, we finish with the computation of routing table from beginning to end.
We have discussed the procedure of computation of the routing table while at the same time respecting
the constraints of leveraging ICMP if present in the topology.
The routing table should be loop free.
And each destination in the topology should be reachable via minimum cost.
Right.
Now, I hope you have got a clear understanding regarding how layer three routers of the topology computes
their respective routing tables.