[dns-operations] Why are cnames called "canonical" names?

[Mark Andrews]

In message <55272FE8.4060408 at easydns.com>, "Mark E. Jeftovic" writes:
> Again, I'm not explaining myself clearly.
> 
> The question isn't "which side of a cname is the canonical name", the
> question is "why did they decide to call it 'canonical'" (as opposed to
> calling it some other word than 'canonical' that meant exactly the same
> thing as what 'canonical' means.
> 
> It's just not intuitive (to me) as to why that specific actual word
> (which has biblical meanings but no ostensible technical ones, read on)
> was selected.
>
> In other words my question is "what is the etymology of the term
> 'canonical' in the sense that it's used in the DNS CNAME RR"
> 
> I hope the person who emailed me off-list does not mind that I paste a
> snippet of what he told me here:
> 
> --begin
> 
> ""canonicalizing" can be found mentioned as early as K&R's _C_ at least
> as a concept (pre-dating the patent nonsense about number formats on the
> wire). It's mentioned in the sense of promotion of numbers.
> 
> In essence the general concept (as it pertains to numbers anyway) is
> that it's a lot easier to write N*2 convertors (one each way) to a
> representational format powerful enough to represent all N formats than
> it is to write N*(N-1) convertors to convert directly between them.
> 
> 
> So "canonicalizing" names doesn't mean quite the same thing but the
> concept is that "WWW" should work everywhere, it's a canonical name for
> a service. They could have just used A RRs, but the responsibility for
> maintaining the service might not be the same as that for infrastructure."
> 
> ---end
> 
> That's the sort of explanation I was after.
> 
> - mark

If you are thinking about "www.example.net CNAME some.hoster" then
CNAME is actually being mis-used.  HTTP developers really should
have requested a new type for this behaviour similar to MX and no
it would not be slower.

In email the MUA was actually required to re-write the RHS of the
address to the canonical name of the host so the renaming would
work.

CNAME records are supposed to be temporary records for transitioning
one name to another.  Well at least that is what the early examples
used them for.  Re-writing of elements was expected to happen when
CNAME records were encountered.

Mark

> Mark Andrews wrote:
> > In message <55272759.9030605 at easydns.com>, "Mark E. Jeftovic" writes:
> >> 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".
> >>
> >> Somebody did send me a very comprehensive background off list which goes
> >> back to Kernighan & Ritchie's "C" book.
> >>
> >> - mark
> > 
> > The target (RHS) of the CNAME is supposed to be the official
> > (canonical) name of the entity (though nameservers are required to
> > handle CNAME chains when this requirement is not being met).
> > 
> > The LHS is the alias.
> > The RHS is the canonical name.
> > 
> > Think of CNAME as "the canonical name of this alias is ..."
> > 
> > Now if were providing a list of alias for this entity then ALIAS would be
> > the right name for the record and more than one of them would be supported.
> > 
> > Mark
> > 
> >> Roland Dobbins wrote:
> >>> On 10 Apr 2015, at 6:26, Mark E. Jeftovic wrote:
> >>>
> >>>> Is it in the "accepted as genuine" sense of "included in the list of
> >>>> sacred books officially accepted as genuine" definition of "canonical"
> >>>> that led to this?
> >>> <http://en.wikipedia.org/wiki/CNAME_record>
> >>>
> >>> -----------------------------------
> >>> Roland Dobbins <rdobbins at arbor.net>
> >>> _______________________________________________
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> >>>
> >> -- 
> >> Mark E. Jeftovic <markjr at easydns.com>
> >> Founder & CEO, easyDNS Technologies Inc.
> >> +1-(416)-535-8672 ext 225
> >> Read my blog: http://markable.com
> >>
> >> _______________________________________________
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> 
> -- 
> Mark E. Jeftovic <markjr at easydns.com>
> Founder & CEO, easyDNS Technologies Inc.
> +1-(416)-535-8672 ext 225
> Read my blog: http://markable.com
> 
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org