Favorite DNS?

Lonnie Olson lists at kittypee.com
Mon Jul 30 14:30:55 MDT 2007


Jonathan Duncan wrote:
>> athena    IN    A    192.168.1.1
>> www    IN    CNAME    athena
>>
>> We imprecisely say stuff like "www is a CNAME for athena."  If we think
>> about the two lines together, though, we will say "192.168.1.1 is the
>> address for athena, and athena is the CNAME for www."  So www is the
>> alias, and athena is the canonical name.

> To quote DJB:
> 
> Don't use [CNAME] if there are any other records for [the fully 
> qualified domain name]. Don't use [CNAME] for common aliases; use [the 
> fully qualified domain name] instead. Remember the wise words of Inigo 
> Montoya: ``You keep using CNAME records. I do not think they mean what 
> you think they mean.''  (http://cr.yp.to/djbdns/tinydns-data.html)

What you say here sounds like you are confusing terms.  It totally 
confused me.

A FQDN (Fully Qualified Domain Name) has nothing to do with the type of 
DNS record you use.

athena (NOT fully qualified)
athena.domain.com. (fully qualified)

Bind format zone snippet

# NOT fully qualified
athena	IN	A	192.168.1.1
www	IN	CNAME	athena

# fully qualified
athena.domain.com.	IN	A	192.168.1.1
www.domain.com.		IN	CNAME	athena.domain.com.

As you can see FQDN is not directly related to the type of DNS record 
you use.  Whether or not you should use a CNAME can be debated, and has 
been.  However the mention of using FQDN names is another discussion 
altogether.

My Opinions:

Re: CNAMEs
CNAMEs are fine to use as long as they don't point to other CNAME 
records.  (See bottles-of-beer example)  They are meant to simplify 
management.  Example: I have to change my IP for my server.  If I use 
CNAME records for www, smtp, pop3, secure, etc, etc, etc.  I only have 
one record to change.  Really it is just a personal preference.

Re: FQDNs
Using an FQDN in a zone file is rarely necessary, unless pointing to a 
name outside the zone the file is for.  Refraining from using FQDN names 
on all records keeps the zone file simple, easy to manage, and does not 
incur much, if any, additional processing to parse.

--lonnie



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