Comment by mesrik

>or even by normal load from someone deciding to split a /8 prefix into /24's

If that kind of happening directly from load of added 25 routes it's quite hard to believe it.

  # 10/8 prefix here only to show how to get number of new routes added.

  $ sipcalc -n 24 10.0.0.0/8 | grep -c Network   
  25
  $

BGP peering routing policies have then been for the good reason constructed in way that they expect advertisements "exact accept" with a prefix-list with that /8 prefix, because that's is expected when peering is agreed even when not explicitly stated by many. This expected best practice following goal to manage and prevent internet routing table being filled with superfluous routes.

But anyway, sudden change from /8 to 25 x /24 without first noticing your peers and giving them time to change that "exact accept;" to "orlonger accept;" is quite sure footgun if you don't know common principles of network management. But usually that kind of screwup blast radius is local mostly local only to that /8 prefix.

Not sure though how that could be technically avoided in BGP protocol or router control-plane (router OS config) design. Policy filters and best practices how to use them have been set for good reason. Not just to irritate and make things harder than they need to be. We certainly did not do that while I was still working.

Right, something else what could happen with that kind of sudden change is. If that peered had also other peers which had instead "orlonger" in place traffic would then switch to that, what could have some side effects like saturated links, slowness or even increased costs. Too bad, and may happen. But principle is that communicate your routing changes in good time before you actually make the changes. That will prevent most of this kind of problems ever happening to you.