>Usually

If only...

BCP 38[0] is nowhere near usual. Lots of networks, including some very problematic big ones (cough Hurricane Electric cough), do not implement it as a matter of course. The AWS Route53 hijack last month which resulted in downtime for a number of sites plus a six figure coin theft[1] could have been prevented by adequate filtering.

0: https://tools.ietf.org/html/bcp38

1: https://arstechnica.com/information-technology/2018/04/suspi...