Hello,
You have a nice topology there. Let's see about your questions!
1. Why both the paths in the topology table have the same Feasible Distance and Administrative Distance?
I believe that you are in fact asking about why they have the same Computed Distance and Reported (or Advertised) Distance. We need to clarify a common misunderstanding on the distances seen in an EIGRP topology table:
P 192.168.1.0/24, 2 successors, FD is 3072
via 192.168.2.1 (3072/2816), GigabitEthernet0/1
via 192.168.3.1 (3072/2816), GigabitEthernet0/0
Green => Feasible Distance
Red => Computed Distance
Blue => Reported Distance
There is only one Feasible Distance for the destination network - the one indicated above in the green color. Contrary to the popular explanation, it is not the current best distance to the destination. In reality, the Feasible Distance is the smallest known distance to the destination since the last time the destination went from Active to Passive state (when the last diffusing computation for that destination ended). The Feasible Distance may be equal to the momentary best distance, or may be even smaller than the momentary best distance, but they are otherwise independent. There is no "feasible distance through a neighbor" - this is wrong. For a given destination, there is exactly one Feasible Distance, not tied to any specific neighbor. Therefore, there is no such thing as "two paths having the same feasible distance". What we really want to say in that case is that the two paths have the same Computed Distance.
The momentary distance through a given neighbor is called the Computed Distance, indicated above in the red color, and that neighbor's own last known distance is called the Reported Distance, indicated in blue. In older materials, the Reported Distance was also called the Advertised Distance, but this name is discouraged because it can be confused with Administrative Distance which is entirely unrelated.
So, in your topology, for the 192.168.1.0/24 destination, Router2 can see the same Computed Distance and Reported Distance through both Router0 and Router1 because both Router0 and Router1 are directly connected to 192.168.1.0/24 and each of them is advertising it with the same metric of 2816 (this is the Reported Distance), and the links of Router2 toward Router0 and Router1 have the same metric themselves (causing the overall Computed Distance to be the same for both neighbors). Indeed, from Router2's perspective, 192.168.1.0/24 can be reached equally either through Router0 or Router1, since you always need to traverse two links - to Router0/Router1, and from that router into the 192.168.1.0/24.
2. To reach 192.168.1.0 network Router2 can also use Router3. Then why is that path not shown in the topology table?
It seems that this is an imperfection in Packet Tracer. On real routers, the show ip eigrp topology all-links on Router2 would show something similar to this:
P 192.168.1.0/24, 2 successors, FD is 3072
via 192.168.2.1 (3072/2816), GigabitEthernet0/1
via 192.168.3.1 (3072/2816), GigabitEthernet0/0
via 192.168.5.2 (3328/3072), GigabitEthernet0/2
Green => Feasible Distance
Red => Computed Distance
Blue => Reported Distance
Note that Router3 would be just as far from the 192.168.1.0/24 as Router2 since it also has to traverse two links before hitting the destination network 192.168.1.0/24. But because of this, Router3 would no longer satisfy the Feasibility Condition that says that we can only use neighbors whose Reported Distance is strictly smaller than our own Feasible Distance. Since it is not true that 3072 < 3072, it means that the Router3 is neither a Successor nor a Feasible Successor, and so cannot be safely used because there is a risk of creating a routing loop this way.
Please feel welcome to ask further!
Best regards,
Peter
