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Date:      Sun, 12 Mar 2000 12:13:55 -0800 (PST)
From:      Ken Bolingbroke <hacker@bolingbroke.com>
To:        FreeBSD Questions List <freebsd-questions@FreeBSD.ORG>
Cc:        Matthew Joseff <mjoseff@hellenco.com>
Subject:   Re: CNAME vs A records (clarification)
Message-ID:  <Pine.BSF.4.21.0003121200150.70708-100000@fremont.bolingbroke.com>
In-Reply-To: <Pine.BSF.4.10.10003121426540.79357-100000@retribution.net>

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On Sun, 12 Mar 2000, Matthew Joseff wrote:

> Can someone correct and/or confirm my understanding of CNAME vs A records:
> 
> CNAME should be used for a host that exists on (potentially) another
> server but uses that domain.
> 
> A records should be used as an alias for a host but co-exists with other
> hosts.
> 
> So:
> 
> www	IN	A	(IP address)
> foo	IN	A	(same IP as www)
> bar	IN	CNAME	(some other IP or hostname)
> etc	IN	A	(bar's hostname)

No, A records are the host addresses, and can only point to an IP
address.  CNAME records are aliases for A records.

A more correct example would be:

 foo	IN	A	192.168.0.1
 www	IN	CNAME	foo
 bar	IN	A	10.0.0.1
 etc	IN	CNAME	bar

And then in your reverse lookup zones, you'd have a PTR record for
192.168.0.1 -> foo and 10.0.0.1 -> bar.

Normally, you should only have a single A record for any specific IP
address and a correponding PTR record that reverses the A's IP and
hostname.  CNAMEs are aliases for 'extra' hostnames on the same IP
address.


> I think I'm confusing myself.

O'Reilly's 'DNS and BIND' is an excellent reference.

Ken Bolingbroke
hacker@bolingbroke.com



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