My question is: Why is point-to-point topology configured in loopback? Is it because of the fact that loopback never goes down unless it is manually shut down or if the router crashes, or, is there/are there another explanation(s).
Most case Loopback never go down- also if you have alternative path outside, this will able to take advantage of this.
But again, what IGP and EGP you running very important.
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Keep in mind that using a loopback is only useful when you have more than one WAN link. In the event of a WAN link failure the topology should reconverge to find a alternative path to the loopback.
In a topology with just one link it makes sense to create the peering with the WAN interface IP.