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Comment by hmart | Hacker News Reader

Look dk domain http://dk resolves even without the subdomain.How's that possible?

Nothing special about a tld resolving. You can put an A record on anything. Many companies set up internal DNS names like "go" or "wiki" so that they resolve to helpful internal tools. This is like a public version of that.

The global top-level domain is a dot (.)

Point your browser to www.google.com. and it will resolve the same.

com. and net. and dk. are top-level domains, but still are "subdomains" under the global ".".

The administrator of the dk tld just pointed a dns record at it.

Just wonder whenever http://./ could exist.

Theoretically, I suspect, this should be possible, as an empty-named A/AAAA records on root DNS servers, although dig(1) and host(1) failed to produce such query for me.

It's owned by the danish top level register. I guess they just added a dns entry for that.

It is "just a domain". Top level at that. If you control it, you can point it to an IP.

There are more, http://shii.org/tech/tld.html

The "to" TLD used to resolve to an URL shortener, producing http://to/xxx urls.

Now it still resolves, however the server doesn't accepts http connections anymore.

The browser is automatically putting "www." in front of "dk" allowing it to resolve. Although the root DNS zone (the implied dot at the end of DNS names) can have A records in it, the current policy only allows A records for (some) nameservers. As a result, the new gTLD program, for example, does not currently allow "bareword domains" because you can't put an A record for the domain by itself in the root zone. (The policy doesn't allow an MX record, either, so email to someone@shop wouldn't be possible without a policy change.) The policy is aimed at keeping the root zone simple, and minimizing the volume of changes.

I don't know a lot about DNS, so correct me if I'm wrong, but this looks like a case where the TLD does have an A record:

    dk.       86400	IN	A	193.163.102.24

In fact, www.dk resolves to a different IP:

    www.dk.   86400	IN	A	212.242.42.44

You're right -- dk. has an A record. It's coming from the dk name servers, though, not from the root zone. (I should have run the query the first time.) You're also absolutely correct that dk and www.dk resolve to different IP addresses. So the root name servers are returning a redirect to the dk name servers, which are providing an A record. (You can see it with "dig +trace dk.") The dk name servers can return whatever they want. I believe the behavior is undefined, though -- where a zone and a parent zone have records in common, they should be consistent. So you may get different behavior from different resolver implementations. (This may help to explain why some people see something at http://dk and some don't.)

Doesn't resolve for me.

http://www.dk redirects to http://www.telenor.dk

This is strange. I was able to resolve the IP using the host command. But curl and ping won't work.

    $ host dk
    dk has address 193.163.102.24
    dk has IPv6 address 2a01:630:0:40:b1a:b1a:2011:1
    $ curl dk
    curl: (6) Couldn't resolve host 'dk'
    $ ping dk
    ping: unknown host dk
    $

EDIT: Putting a . behind dk solves the problem.

working here , thanks for sharing .

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