[merlyn]

Correct, what RFC2317 brings you, is an example of you creating a new namespace in some structured format (IIRC, there are three different example formats given in this RFC), and you just have the upstream ISP, which has the reverse delegation done on the zone cut boundary for the IP ranges it controls inserting a CNAME out to your new namespace on nameservers you control for the reverse PTRs so the reverse PTRs can be formed that way.

Running a long time ISP, I found extremely few customers wanting to do something like RFC2317, or could actually figure out and do it effectively. Almost all were content with control panel/API and having the ISP do it after I pointed them to this informational RFC asking them if this is what they wanted.

[anonymousiam]

I think part of the reason most ISPs don't support RFC2317 or reverse delegation is that it makes it easy for a bad actor who's in charge of the DNS server being delegated to, to spoof any domain they want. The consequences of this sort of spoofing have now been limited by other systems and protocols anyway, so it's not as big of a deal.

ISPs prefer to have direct control of the reverse lookups within their IP blocks so they can ensure the integrity of the information.