FW: DNS Question

[Sean Cavanaugh]

> Date: Fri, 23 Oct 2009 08:30:08 -0400
> From: dave.list at pixelhammer.com
> To: freebsd-questions at freebsd.org
> 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