I have an understanding about RIP options that to some extent contradicts with the text books.
I understand that the hold-time is used to give the network enough time to converge so to avoid false updates that may cause loops. Hold-time is one of the reasons for which RIP is considered as a slow protocol.
That is fine up to now. However, the split-horizon option can take care of loops problem, then why do we need the hold-time which causes latency. The answer can be that the hold-time is required in case of circular topology where the false update about a down route may still reach the router from the other side even if split-horizon is used.
Okay, that is fine. However, as far as hold-down time is used along with the split horizon, this means that the hold-down is preventing loops not the split-horizon as even if there is no split horizon, hold-down time will be good enough to stop the loops alone.
In other words, split-horizon is good enough to avoid loops in non-circular topologies while hold-down can stop loops in both cases (circular and non-circular). That means there is no advantage in stopping the loops by applying both methods. Split-horizon alone will be good enough for non-circular topologies (so RIP can work faster without the hold-time here). While hold-time is good enough to stop the loops in circular topologies (so no more advantage in stopping loops by having split-horizon also applied in this scenario).
Then why we get both of them usually applied? The only thing I can find here is that split-horizon saves the bandwidth but does not help in stopping the loops if the hold-down timer is used. Am I right?
Generally, according to my understanding, I am advising to use split-horizon alone for non-circular topology by making the hold-timer = 0. Is it possible? And in case of circular topologies, we need to apply both, hold-timer to prevent loops and split-horizon to save the bandwidth NOT to stop the loops. Am I right?
The other issue is about poison-reverse. I do not understand how it can help by breaking the split-horizon rule and advertising infinite routes to the same interface from where it got the update. I hope you can help me in that.