DNS Question

DAve dave.list at pixelhammer.com
Fri Oct 23 15:12:34 UTC 2009

Sean Cavanaugh wrote:
>  > 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 <http://www.bobshosting.com>    A
> www.vhost1.com <http://www.vhost1.com>          CNAME  
> www.bobshosting.com <http://www.bobshosting.com>.
> www.vhost2.com <http://www.vhost2.com>          CNAME  
> www.bobshosting.com <http://www.bobshosting.com>.
> www.vhost3.com <http://www.vhost3.com>          CNAME  
> www.bobshosting.com <http://www.bobshosting.com>.
> www.vhost4.com <http://www.vhost4.com>          CNAME  
> www.bobshosting.com <http://www.bobshosting.com>.
> -Sean

All true, and I did not do a very good job of explaining it. My issue 
was that we have requests to use a CNAME for the domain record. Such as 

example.com  CNAME  otherdomain.com
www.example.com  CNAME   otherdomain.com

I was taught this was not good form, but allowed. I can deal with it. 
But what of having a SOA record for example.com, no A or CNAME record 
for the TLD example.com, only hosts such as www, ns1, ftp, etc.

I tried it an it seems to work fine, but doesn't look proper to me. Then 
again I remember when CNAME were considered evil.


"Posterity, you will know how much it cost the present generation to
preserve your freedom.  I hope you will make good use of it.  If you
do not, I shall repent in heaven that ever I took half the pains to
preserve it." John Quincy Adams


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