[dns-operations] Why are cnames called "canonical" names?
Kumar.Ashutosh at microsoft.com
Fri Apr 10 16:59:42 UTC 2015
Because the RDATA contains the true name.
The record name is an alias to the true name.
From: dns-operations [mailto:dns-operations-bounces at dns-oarc.net] On Behalf Of Mark Andrews
Sent: Friday, April 10, 2015 08:33
To: Evan Hunt
Cc: dns-operations at lists.dns-oarc.net
Subject: Re: [dns-operations] Why are cnames called "canonical" names?
In message <20150410023644.GA24751 at isc.org>, Evan Hunt writes:
> On Thu, Apr 09, 2015 at 09:28:57PM -0400, Mark E. Jeftovic wrote:
> > Thanks but that page doesn't go into why the term "canonical" was
> > adopted, as opposed to "alias" (which makes sense), or even
> > "knickname", "doppelganger" or something like "pointer".
> Read it as: (thing on the right) is the (type) of (thing on the left).
> "example.com. IN A 192.0.2.20" means "192.0.2.20 is the address of
> example.com". Similarly, "www.example.com. IN CNAME xyzzy.example.com."
> means "xyzzy is the canonical name for www" (i.e., the true and
> correct name).
> If CNAME had been called ALIAS, then the line above would have been
> saying "xyzzy is an alias for www", but that's the opposite of what it's saying.
> www is the alias, and xyzzy is the real name of the server hosting it.
> I doubt anybody was anticipating CDNs in those days; everybody
> probably figured a CNAME RR would always point to the *one and only*
> true and correct hostname, instead of having multiple levels of
> indirection like you see if you look at "dig www.paypal.com" nowadays,
> so it made sense to refer to that as canonical. (Add it to the list of
> ways the DNS might have come out differently if we'd had a crystal
CNAME is not "IS-HOSTED-BY" but it is used like IS-HOSTED-BY for HTTP.
If you http://LHS/foo and http://RHS/foo do not get the same thing for all possible foo then you are mis-using CNAME. Yes, there is a lot of mis-use of CNAME.
> Evan Hunt -- each at isc.org
> Internet Systems Consortium, Inc.
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Mark Andrews, ISC
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