Hello David
This is a great experiment to determine how these routing protocols behave when there is more than one entry point between multiple routing domains.
Let me say first of all that a routing loop is not necessarily present simply because there are two entries in the routing table. Yes, in your first scenario, R1 sees a valid route to the 192.168.1.0/24 network via R5 as well as R2. A routing loop will only be confirmed if you take a look at the routing tables of all routers in the alleged loop and see that they route to each other.
For example, for the 192.168.1.0/24 destination,
- if R1 routes traffic to R2,
- and R2 routes this traffic to R4,
- and if R4 routes this traffic to R3,
- and if R3 routes this traffic back to R1,
…only then will you confirm a routing loop.
Having said that however, what you see in the routing table of R1 would be considered sub optimal routing at best.
This depends upon the metric of the route learned from R3. Remember, RIP will only install routes of equal cost. R1 may have received the route from R3, but the metric may be higher for some reason, and it was not installed. You can use debugs or packet captures to determine if such RIP updates were sent from R3.
Again, the fact that you see only one next hop doesn’t mean that the destination wasn’t re-redistributed into the EIGRP domain. It simply means that the metric was not the same, so it was not installed in the routing table.
I hope this has been helpful!
Laz