There are domains, that are registered in DNS with a SOA-record only, but without any A-record (or any other records):
> dig wien.eu
; <<>> DiG 9.9.7-P3 <<>> wien.eu
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51354
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;wien.eu. IN A
;; AUTHORITY SECTION:
wien.eu. 1922 IN SOA dns1.magwien.gv.at. hostmaster.magwien.gv.at. 2013082700 10800 3600 604800 86400
;; Query time: 134 msec
;; SERVER: 192.168.0.1#53(192.168.0.1)
;; WHEN: Sat Dec 02 19:45:19 CET 2017
;; MSG SIZE rcvd: 101
What looks like an A record is just a comment (it starts with a semicolon). Even if it wasn't a comment, it would be malformed (i.e. not an A record) because it contains no IP address.
Most commands, that usually resolve domain-names (like ping, telnet and others) using DNS will fail if there is nothing but a SOA entry (and lots of comments and empty lines).
Also many webbrowsers are unable to open a website on such a SOA-only-domain, like http://wien.eu, among them:
- Google Chrome
- Opera
- Tor Browser
But there are browsers that will open a website if you enter such a domain name:
- Safari
- Firefox
I couldn't test Internet Explorer, because I use Mac OS, and it's not available there.
In case of the given example they redirect to another URL (which btw. looks like a meaningful way to resolve the given URL, which makes me believe to be the desired behavior).
I wonder, what Safari and Firefox do to perform this miracle, that other browsers and tools can't do.
btw: I thought to know how DNS works, and I thought, this would mean, that SOA-only-domains like wien.eu can't be resolved to an IP-address. But Safari and Firefox prove the opposite.
Addendum in reaction to an answer.
All 5 browsers used in my test are the newest versions, and all of them run on the same computer (iMac with Mac OS X 10.13 High Sierra). So they all use exactly the same Operating System and they also use exactly the same DNS-Server.
And there is no AAAA-Record in the zone-file (as you can see in the quoted output of dig above).
And if you can't believe it: Try it out. Use any tool you want to check the DNS settings of wien.eu and try to open it in two different browser that belong to each of the both groups listed above.
https://www.wien.gv.at/
. I understand the redirection, but I do not understand how the domain name resolution works in this case.