On 22 Jan 2018, at 22:31 (-0500), li...@lazygranch.com wrote:
So if I do a reverse DNS lookup on some IP addresses, I will get multiple domains?
Yes, as long as you use a DNS resolution tool and not a client of the abstracted name resolver of your OS (which may use a complex federation of naming services.) I had multiple PTRs for a dozen years on my external NAT addresses when my IP provider was willing to delegate authority for my in-addr.arpa space to my nameserver. It never caused any problem more significant than confused humans. The legacy standard resolver functions (gethostbyname & gethostbyaddr) accommodate the potential many-to-many mapping of addresses and names, but for reasons I don't understand, the modern standard reverse resolution function (getnameinfo) does not.
There is imprecise language in RFC1035 (1987) implying that there should be only one PTR per IP but it depends on the idea of a "primary host name" for an IP, which is not universally meaningful or useful as a naming concept.
-- Bill Cole b...@scconsult.com or billc...@apache.org (AKA @grumpybozo and many *@billmail.scconsult.com addresses) Currently Seeking Steady Work: https://linkedin.com/in/billcole
