FW: DNS Question

Sean Cavanaugh millenia2000 at hotmail.com
Fri Oct 23 16:18:53 UTC 2009

> Date: Fri, 23 Oct 2009 17:17:48 +0200
> From: lconrad at Go2France.com
> To: freebsd-questions at freebsd.org
> Subject: Re: DNS Question
> >
> >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 
> >this.
> >
> >example.com CNAME otherdomain.com
> >www.example.com CNAME otherdomain.com
> >
> >I was taught this was not good form
> worse, it's illegal.

how is this illegal? if you are residing your domain on a hosting service, this makes sense to me. Granted its bad form and should have an A record to the host for the main domain record, but if i had control over "otherdomain.com" and not "example.com" and had to change the IP address, "example.com" would be dead until i was able to reach the owner of that domain and have them change their DNS info. 
> , 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.
> CNAMEs are still evil, unless 
> 1) no other solution exists and 
> 2) the user knows how to use CNAMEs (rare).
> Len

there is nothing that says you HAVE to have your tld labled in DNS. you would just run into issues if someone types http://example.com into their web browser and not get a result in DNS.  

to clarify on CNAME's a bit better. CNAME's are nothing more than DNS aliases. the reason you do not want to overuse them is that you could potentially create a loop if you are not careful
www.site1.com     CNAME    www.host1.com.
www.host1.com    CNAME    www.site1.com.
syntactically, this is correct but would cause an infinite loop until a timeout occurred on your computer.
also you want to limit how many weird names you get associated to one box. it makes sense if you want www.example.com to point to your web server, which you may have officially called "srvWeb", but looking at things like a mail server, would you rather only have the entry:
mail.example.com    CNAME    srvMail.example.com.
or have to edit this:
pop3.example.com    CNAME    srvMail.example.com.
smtp.example.com    CNAME    srvMail.example.com.
imap.example.com    CNAME    srvMail.example.com.
The other interesting side would be reverse DNS lookups. Only one record would be returned, and most likely would be the original A record. A nice example of this is doing a basic "ping -a www.yahoo.com" which you get back that it is resolving "www-real.wa1.b.yahoo.com".


More information about the freebsd-questions mailing list