Hello Jugal
Yes that is correct.
Hmm, it depends on what you mean exactly when you say “control plane looping.” Another phrase for this is “lack of OSPF convergence.” The term “control plane” indicates that OSPF messages are being sent continuously and looping throughout the topology, which indicates a lack of convergence. This is something different from routing loops which direct user traffic to loop indefinitely throughout a topology. Such loops in this context may be considered considered data plane loops. But these phrases aren’t standardized, so that’s why I’m clarifying it here. Is this what you are referring to?
The three points that you mention as methods of mitigation of loops are used to mitigate against routing loops, not lack of OSPF convergence.
What points 2 and 3 are saying is that αn ABR will normally only accept and propagate summary routes from Area 0 to ensure a consistent and loop-free routing environment. By limiting the propagation of summary routes from Area 0 only, OSPF ensures that routing information is disseminated in a hierarchical manner. This reduces the complexity of route propagation and the risk of loops.
However, if an ABR loses all full adjacencies with Area 0, it can accept summary routes from a non-backbone area as a temporary measure to maintain network connectivity. This behavior is designed to preserve the integrity and stability of the OSPF routing domain while providing flexibility to handle exceptional situations where backbone connectivity is temporarily lost.
Take a look at this lesson that talks about he P-bit in detail:
If you still have questions after going through this, let us know and we’ll address them.
I hope this has been helpful!
Laz