Sites that points their A Record to localhost
Kevin Darcy
kcd at chrysler.com
Wed Jan 15 00:55:44 UTC 2014
If the domain owner *really* feels that they have to publish *some*
address record for a particular name, but there is no available service
at that name, then the null or "unspecified" address (IPv4 = 0.0.0.0,
IPv6 = ::0) is the appropriate value to put there.
Loopback is anti-social; an apparent attempt to make the client waste
resources connecting to itself. In legal terms, one might call this an
"attractive nuisance".
- Kevin
P.S. I wish more load-balancer vendors would understand, appreciate and
adopt the use of the null/unspecified address to mean "no service
available here".
P.P.S. I credit Mark Andrews for opening my eyes to the proper use of
null/unspecified.
On 1/10/2014 11:36 PM, Joseph S D Yao wrote:
> On 2014-01-10 15:01, Eduardo Bonsi wrote:
> ...
>> It seems like they have their domain configuration A Record pointed
>> to the localhost. We all know that the localhost is not routable
>> outside of the internet. Therefore I am sure their website cannot
>> resolve out of the 127.0.0.1.
>> In addition to that, it is possible that this is happening only here
>> because of the way our Server configuration is setup in the OS X to
>> bring the resolver to the localhost first before it can go out to the
>> distributed domains/websites through the Apache conf.
> ...
>
>
> There seems to be a pile of misconceptions here.
>
> (1) There is no requirement at all that a domain name have an A
> record. It does not have to resolve to an IP address at all. It only
> has to have an SOA record and an NS record (preferably more than one);
> and not even that, if it is a subdomain that is not a separate zone.
>
> (2) There is no requirement that a domain name refer to the Web site
> for that domain. I personally don't like that (for no special
> reason), and neither apparently does the owner of this domain, who
> forces people to go to the trouble of typing in www.p3net.net to get
> to his or her Web site. Incidentally, there is no requirement that
> the domain name refer to a mail server, either (which used to be
> common before the Web existed), or to an FTP server, or to a Telnet
> server, or to a nuclear reactor control device. Or to anything.
>
> (3) However, any name MAY resolve to any IP address, routable or not.
> That doesn't mean there's anything useful, or even related to that
> domain, at that IP address.
>
> (4) "127.0.0.1" is the IP equivalent of the English language word
> "me". If I say, "me", I am referring to myself. If you say, "me", you
> are referring to yourself. It cannot be used to direct anyone to
> somewhere else. In fact, some use it to deflect probers AWAY from
> themselves, and back on the prober's own server. (E.g., if I wanted
> to probe "p3net.net", my server would be probing itself!)
>
> (5) 127.0.0.1 is not among the IP addresses mislabeled as
> "unroutable". It is always routable. To right here. Well, for you,
> right there.
>
> (6) Just because OS X has 127.0.0.1 as the resolver has no effect on
> what that resolver returns. Don't confuse the concepts.
>
> I think there were some others, but it's getting late.
>
> Joe Yao
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