Date: Fri, 23 Oct 2009 13:49:19 +0100 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: DAve <dave.list@pixelhammer.com> Cc: 'User Questions' <freebsd-questions@freebsd.org> Subject: Re: DNS Question Message-ID: <4AE1A64F.1000405@infracaninophile.co.uk> In-Reply-To: <4AE1A1D0.8060402@pixelhammer.com> References: <4AE1A1D0.8060402@pixelhammer.com>
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DAve wrote:
> Good morning.
>=20
> I have been asked by my co-workers and sales why I always create a A=20
> record for new domains we host instead of a CNAME.
>=20
> The issue I run into lately with some domains is that a client has a=20
> website with a industry host such as frank.relator.com and he wants to =
> have DNS point www.frank.com to frank.relator.com with a CNAME. The=20
> client does not want an A record for frank.com.
>=20
> Somewhere, in a class far far away, I was taught a DNS zone had to have=
=20
> a A record to function properly. I can't seem to locate anything in the=
=20
> RFCs.
>=20
> Am I wrong?
Yes, you're wrong.
In terms of web service, you can use either an A record or a CNAME record=
to provide the address part of a site's URL[*]. As far as the web server=
is
concerned, it looks for the 'Host=3D' line in the HTTP packet to decide w=
hat
name-based VHOST to dispatch the query to internally, and doesn't necessa=
rily
do any DNS lookups at all. Web clients just do a gethostbyname(3) or get=
addrinfo(3) call to resolve the site name into an IP, and anything suppo=
rted by those (/etc/hosts, NIS, LDAP, DNS) will do the trick.
In terms of the DNS a 'Zone' is a delegated block of the name space under=
a single administrative control. Typically with BIND this maps onto a si=
ngle
'Zone file' containing all of the DNS resource records for the zone. The=
only records a zone *has* to have are:
* 1 SOA record, with the zone serial number
* Some number of NS records giving the nameservers for the zone.
It's perfectly permissible to have a zone that doesn't contain any A
records (or AAAA records) and in fact, reasonably common: reverse domains=
generally contain mostly PTR records.=20
Cheers,
Matthew
[*] Possibly others, but A and CNAME are the vast majority. Being able t=
o
use SRV for webservers would be cool.
--=20
Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard
Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate
Kent, CT11 9PW
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