Yeah it's bonkers they allow this still. No good actor ISP is going to knowingly let improperly sourced traffic transit networks...

Oh how I wish that was actually true.

I mean, yes there are bad actor ISP's that allow it, but his statement is accurate due to the caveat.

The middle (ntt, gtt, tata, etc) of the internet doesn't know what is or isn't spoofed. The folks at the edge own that responsibility and most colo/hosting shops allow their customers to spoof. Their upstreams are powerless against them since they'll take their money elsewhere.

Lol, that’s not the definition of “powerless”. There are many ISPs more than willing to reject peering with dumpsters.

Not talking about peering. Talking about transit-customer relationships. Think large hosting shops who say they can't afford to do uRPF on their customers because they've got so many multihomed users and the IP address space is fluid. Or smaller regional networks selling low cost transit. Some folks just have arbitrary limits (you must have x asns behind you for us to remove urpf)

Yeah, one would think that a national phone carrier would only send through properly sourced data. But I can tell you from experience that no, they let through garbage. I regularly see "phone numbers" like "11111111111111" or "0000000000" or even "01120155512121234". They act like they're the phone company and don't have to care ...