Icelandic domains (.is) require that their domains support reverse DNS, which means configuring PTR records on the hosting server.
Is it possible to set up a PTR record for GitHub Pages site hosting?
Background:
I have an Icelandic top-level domain - petejones.is - and am using CloudFlare for DNS and GitHub Pages for hosting. Icelandic domains are a little unusual in that .is domains must be registered through the national registrar ISNIC, and they have some tougher (it seems) requirements that the registered domains must comply with.
Apparently my setup is not quite up to snuff, as I've just gotten a notice from them that my DNS is not configured correctly. Here's the key bit:
Test results for "DREW.NS.CLOUDFLARE.COM": The IP address
2400:cb00:2049:########## of nameserver jasmine.ns.cloudflare.com
is missing its PTR record or has an incorrect PTR record. The IP
address 2400:cb00:2049:########## of nameserver
drew.ns.cloudflare.com is missing its PTR record or has an incorrect
PTR record. Test results for "JASMINE.NS.CLOUDFLARE.COM":
My sophisticated research (quick googling) indicates that ISNIC is testing to make sure the domain supports reverse DNS - you can resolve the IP from the domain name and vice versa - which seems to be a way of discouraging spam email domains.
Apparently this is configured on the host, rather than the DNS, which makes sense given that the goal is to find the domain from the host.
Is this possible on GitHub Pages? I've seen plenty of info on adding A or CNAME records but nothing about PTR records. I suspect GitHub doesn't get a lot of requests for this because they aren't concerned with email delivery.
Answer
The warning that you're seeing there isn't actually about GitHub or GitHub pages at all, but about CloudFlare's name servers.
Personally, I'd argue that accurate PTR on a name server's IPv6 address really isn't a problem, per se - email is going to care about reverse resolution for the mail server, not the DNS server. We know the DNS server is valid for the domain because it's been delegated to; ensuring the owner of the IP space has named it identically is a pointless exercise.
However, CloudFlare would probably be interested in being compatible with the .is registrar's desires; you should drop them a note and they might happily fix.
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