[ enumerate domains for which a nameserver publishes authoritative data ] Even if the nameserver _did_ allow zone transfers, you _still_ couldn't enumerate its zones. Even if you "parsed all registration sites" you'd still be nowhere near there. Any subdomain at any depth can be delegated, by any nameserver. And a server can offer authoritative data even if nobody delegates it at 'em, this is sometimes a very useful technique, e.g. declaring SOA for a classfully-aligned superset of your real classless delegation in in-addr.arpa. And one of the more popular top-level zones, .com, is jealously guarded as a secret by the lucky bastards who stole it from the public domain, to prevent other folks from stepping in and doing a more responsible job of managing registry for the domain. The place where this question rises routinely is in DNS server sets. It's quite common within organizations to want to maintain sets of domains across some collection of more or less independent nameservers. DNS has a protocol within it, zone transfer, for replicating the contents of a zone; not the best-designed protocol, but occasionally useful. But as it has no mechanism for enumerating the zones that would need to be transferred, some out-of-band mechanism needs to be used to maintain the zone list; and once that's in place, many folks note that using common off-the-shelf components for replication works better than zone xfer even for the zone data. The one place zone xfer is handy is as a rendesvous point; nameservers with different native zone data formats can share zone xfer as a way to convert zones from one format to another. -Bennett
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