Domain name as hostname not recommended

I had an interesting support ticket yesterday.

Someone was trying to do an apt-get update via BitFolk‘s apt cache and was ending up connecting to 2607:f0d0:1003:85::c40a:2942, where it was failing to update. This is not a BitFolk IPv6 address, nor is it the IPv6 address of a Debian mirror. Where was it coming from?

I’d asked the customer for the contents of a bunch of config files and output of the dig command, and while I was waiting for that I mentioned the problem on IRC, where Graham said:

<gdb> $ dig -t aaaa +short
<gdb> 2a00:1c10:3:634::3486:75a0
<gdb> 2607:f0d0:1003:85::c40a:2942
<grifferz> interesting
<gdb> Same for
<grifferz> so he's probably got some  search line in
           his resolv.conf
<gdb> I would ask what the search line is
<grifferz> r
<grifferz> search lines always good entertainment for
           those times when wtf moments are scarce
<gdb> Actually it's possible that the hostname is and there's no search line.

It seems that the enterprising folks at have put in wildcard A and AAAA records which basically means that if you try to resolve * you end up at their “search portal”. That’s all web-based of course.

The customer didn’t have a search line, but the issue was that their host had a fully-qualified domain name (FQDN) along the lines of

This meant that according to default resolver settings it considered itself to be inside the domain net, and when searching for hosts (like it would try to find them with .net appended first.

Massively confusing.

It can be fixed by giving the resolver libraries a hint as to which domain you are actually in, in the /etc/resolv.conf:


Having said that, it’s better not to pick your domain as the FQDN for any host and this is just one of the weird issues I have seen.

Sometimes customers order a VPS with a FQDN set to something like this, and I’ve yearned for an authoritative bit of documentation that says it’s not recommended. I asked about it on HantsLUG a while back also, and while it seems there was some agreement, it still seems to be down to preference.

I’ve never really tried to tell a prospective customer that they should pick a host within their domain (e.g. instead of the domain name as the FQDN, because it always seemed like too complicated a subject to explain. Maybe I should try to find a way in future.