Re: FW: DNS Question
- From: "Len Conrad" <lconrad@xxxxxxxxxxxxx>
- Date: Fri, 23 Oct 2009 17:15:09 +0200
---------- Original Message ----------------------------------
From: krad <kraduk@xxxxxxxxxxxxxx>
Date: Fri, 23 Oct 2009 15:56:40 +0100
2009/10/23 Sean Cavanaugh <millenia2000@xxxxxxxxxxx>
Date: Fri, 23 Oct 2009 08:30:08 -0400
From: dave.list@xxxxxxxxxxxxxxx
To: freebsd-questions@xxxxxxxxxxx
Subject: DNS Question
Good morning.
I have been asked by my co-workers and sales why I always create a A
record for new domains we host instead of a CNAME.
The issue I run into lately with some domains is that a client has a
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
client does not want an A record for frank.com.
Somewhere, in a class far far away, I was taught a DNS zone had to have
a A record to function properly. I can't seem to locate anything in the
RFCs.
Am I wrong?
I think you are confusing basics of DNS records. you are partially correct
in that a DNS zone needs an initial A record to be able to translate a name
to an IP, but there is nothing wrong about setting up a CNAME to point to a
record in a different zone instead. you just cannot do a zone that has a
CNAME only that does not at some point to a valid A record. CNAMEs are
forwarders only whereas A records are actual lookups.
for proper way to set this up....
The A record would be assigned for the main name that you want to associate
to an IP address.
The CNAME record just relates a different name to that original name. this
allows you to change the IP address of the server and only have to update
the original A record instead of every DNS record for that server.
for small number of vhosts, this would not really be an issue, but imagine
if you were hosting a couple hundred vhosts from a single IP and then had to
change that IP because you switched your ISP. It would take you a LONG time
to update them if they were all A records, but only a couple of seconds if
you had it properly set up as CNAME's
www.bobshosting.com A 192.168.0.1
www.vhost1.com CNAME www.bobshosting.com.
www.vhost2.com CNAME www.bobshosting.com.
www.vhost3.com CNAME www.bobshosting.com.
www.vhost4.com CNAME www.bobshosting.com.
-Sean
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I try to use CNAMES as much as possible, for one very good reason. If say I
have web server with 1000 vhost on it. I have one A record for the server
and all the cnames point at that A record. Now i need to change the ip of
the server. I update the A record and add a reverse record and im done. IF I
had done it your way with all A records I would now have to go and edit
another 1000 records. Even worse if some of these domains are not under my
control I have to go and liaise with customers, or other third parties, and
it becomes a complete mess. The chances of me convincing them all and
coordinated it correctly are minimal 8(
domains sharing records is better handled by $INCLUDE
$INCLUDE /path/db.ttl, which contains
$TTL 6h
$INCLUDE /path/db.ns, which contains
@ ns ns1.domain.tld.
@ ns ns2.domain.tld.
$INCLUDE /path/db.www, which contains
@ a ip.ad.re.ss
www a ip.ad.re.ss
etc.
Changing an include file changes all the zone files that include it, giving enormous leverage, while removing the extra query required to resolve a CNAME to canonical.
Len
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