DNS loop

[Simon Waters]

Jeffrey Keil wrote:
> 
> The SOA line reads:
> 
> @       IN      SOA     mail.gcs-usa.com. dalton.gcs-usa.com.
> 
> The same machine is listed as one of the DNS servers with the
> following line:
> 
> IN    NS    ns1.gcs-usa.com.
> 
> He has the different machine names and the same IP address listed
> three times in the list of addresses for canonical names:
> 
> mail                    IN      A       192.168.1.32    ; Mail Server
> for GCS
> osx                     IN      A       192.168.1.32    ; Mail Server
> for GCS
> ns1                     IN      A       192.168.1.32    ; DNS Primary
> Server
> 
> I didn't think you were allowed to use the same IP address more than
> once. I'm a little surprised that BIND allows something like this in
> the configuration file. Wouldn't this create a DNS look?
No this is perfectly valid as far as I can see.

How would it create a loop, DNS looks up the left hand side and returns
the right, and A records are always a terminal node, only CNAMEs (or
similar) can lead to problems which is why they are so restricted in
their use.

> I think the best way to fix this would be to change the DNS server
> designation from ns1.gcs-usa.com to mail.gcs-usa.com with a line like
> this:
> 
> IN    NS    mail.gcs-usa.com.
> 
> I could then list the two other names (osx and ns1) as aliases with
> lines that look like this:
> 
> osx                   IN   CNAME   mail
> ns1                   IN   CNAME   mail

ns1 is a delegated name server from the .com servers, so you should
update them to delegate to "mail" if you did this, to avoid delegating
to something that is a CNAME.

> Does anyone have a better suggestion?

I'd be tempted to leave it as is, or maybe change the SOA record to
refer to NS1, CNAMEs are evil(ish)


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