CNAME RRs

[Terrence Koeman]

Hello,

I have been following this discussion, and I'm really consufed now :)

As I see it, Men&Mice states:

--- CUT ---
A domain name that has a CNAME record can't have any children. So if glossary.example.com has a CNAME record, Then jobs.glossary.example.com is improper.
--- CUT ---

This means for me that when you have this:

subdomain.domain.tld.  IN  CNAME  host.domain.tld.

You cannot have any records for "host.subdomain.domain.tld.", thus anything ending in "subdomain.domain.tld.". OK, at first sight this could be true, as CNAMEs are strange records and there are all sorts of things you cannot, and must not do with them.

I have been reading some RFCs that deal with RRs, but I coudn't find anything about this. But there isn't a single example in a RFC that violates the above statement

Now a very wild guess, I'm not a DNS expert so correct me if I'm wrong:

Isn't

subdomain.domain.tld.  IN  CNAME  host.domain.tld.
host.subdomain.domain.tld.  IN  A  0.0.0.0

the same thing as:

[zone - domain.tld.]
subdomain  IN  CNAME  host.domain.tld.
subdomain  IN  NS  <same nameserver as domain.tld.>

[zone - subdomain.domain.tld.]
host  IN  A  0.0.0.0

If it is, then the statement of Men&Mice is correct as there cannot be any other record besides a CNAME, and in this case there is a NS record and a CNAME record for the subdomain.domain.tld. zone.

I guess this depends on how a DNS server handles the "subdomain.domain.tld." and "host.subdomain.domain.tld." in the same zonefile internally. Does a DNS server assume a 'delegation' to itself for the "subdomain.domain.tld."?

-- 
Regards,

Terrence Koeman

Technical Director/Administrator
MediaMonks B.V. (www.mediamonks.nl)

Please quote all replies in correspondence. 

> -----Original Message-----
> From: bind-users-bounce at isc.org [mailto:bind-users-bounce at isc.org]On
> Behalf Of pelln at icke-reklam.ipsec.nu.invalid
> Sent: Thursday, September 20, 2001 9:59 PM
> To: comp-protocols-dns-bind at moderators.isc.org
> Subject: Re: CNAME RRs
> 
> 
> 
> Barry Margolin <barmar at genuity.net> wrote:
> > In article <9oddtg$12q at pub3.rc.vix.com>,
> >  <pelln at icke-reklam.ipsec.nu.invalid> wrote:
> >>
> >>Richard Willmann <mailinglists at nocomment.sk> wrote:
> >>
> >>> hello,
> >>
> >>>  i would like to ask according to DNS glossary founded on 
> Men&Mice web site
> >>> about CNAME RRs. The CNAME RR according to RFC1035 can not 
> share owner name
> >>> with any other RR. But, this time I have found following statement:
> >>
> >>> --- CUT ---
> >>> A domain name that has a CNAME record can't have any children. So if
> >>> glossary.example.com has a CNAME record, Then 
> jobs.glossary.example.com is
> >>> improper.
> >>> --- CUT ---
> >>
> >>It means that one cannot have a subdomain glossary.example.com 
> ( or antithing
> >>else named "glossary.example.com"
> >>
> >>In the zonefile for example.com it's perfectly ok to have :
> >>glossary.example.com.	IN	CNAME <somewhere else>
> >>jobs.glossary.example.com IN    A	1.2.3.4
> 
> > Isn't that exactly what the second sentence in the quote says 
> is *not* OK?
> > So are you agreeing with the quote or disagreeing with it?
> No. there is no zone "glossary.example.com", and nothing else called
> "glossary.example.com" 
> 
> 
> If there was a delegated zone by the name "glossary.example.com" it would
> conflict with the cname.
> 
> > As I wrote earlier, I believe that these entries are OK, and 
> the claim from
> > Men&Mice is wrong.
> Again, there is exactly one item called "glossary.example.com" and that
> is a cname. Nothing violated here.
> 
> 
> > -- 
> > Barry Margolin, barmar at genuity.net
> > Genuity, Woburn, MA
> > *** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to 
> newsgroups.
> > Please DON'T copy followups to me -- I'll assume it wasn't 
> posted to the group.
> 
> 
> 
> -- 
> Peter Håkanson         
>         IPSec  Sverige      (At the Riverside of Gothenburg, home 
> of Volvo)
>            Sorry about my e-mail address, but i'm trying to keep spam out.
> 	   Remove "icke-reklam"and "invalid"  and it works.
> 
> 
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