CName Terminology Question

[Hongbo Shi]

From: Jeremy Lunn <jeremyl at vicnet.net.au>
Subject: Re: CName Terminology Question
Date: Thu, 13 Apr 2000 21:13:44 +1000

> bar.com               IN A      37.124.19.7
> foo.bar.com           IN CNAME  bar.com.
> > 
> > These will all work, but is the "Cname" the part on the left or the part on
> > the right in the line above?
> 
> I still don't understand you...
 
 If I am not wrong, I think maybe he or she wants to describe in 
 "foo.bar.com IN CNAME bar.com."which one is the alias and which one is 
 the canonical name. And if his or her question is this, the answer is 
 foo.bar.com is the alias of the domain name bar.com. Also we can say, 
 the domain name bar.com is the canonical name of the domain name 
 foo.bar.com. 

From: "Walt Brannon" <walt at web-3.com>
Subject: CName Terminology Question
Date: Thu, 13 Apr 2000 06:03:56 -0500

> 
> 	I know this is a very small point, but I see this used in ways that is
> ambiguous on this list so I thought I would ask to get it straight.
> 
> 	In the zone file for bar.com we can have these two types of records (among
> others):  A records and Cname records.
> 
> 	I have alwyas thought that an A record pointed TO an IP address  ie,
> 37.124.19.7 and I thought that a CName record pointed to the Cannocical
> Name, ie, domain.com  so then "foo" in foo.bar.com is not the CName but the
> alias to the Canonical Name.
> 
> 	I see the use of "the alias (cname) ...." that it is confusing.
> 
> For example:
> 
> bar.com 		IN A 37.124.19.7
> foo.bar.com.  	IN A 37.124.19.7
> 
> foo.bar.com.   	IN CName   bar.com
> ...
> Which is correct?

 About the zone file what you said above, I think it is a very 
 interesting question and also very important. If they all work,
 I think they works differently.
 If you set your zone file in this way,
 bar.com        IN A 37.124.19.7
 foo.bar.com.  	IN A 37.124.19.7
 When you send a query for asking the corresponding IP address for 
 foo.bar.com, you will find the nameserver looks up the foo.bar.com
 as a canonical name in the zone file you set, not an alias. Then 
 the namesever will just get the IP address and give you the reply.
 So the relation of your set is 
  "foo.bar.com -> 37.124.19.7" .

 On the other hand, if you set your zone file in this way, 
 bar.com       IN  A      37.124.19.7
 foo.bar.com.  IN  CNAME  bar.com
 When you send a query for the same domain name foo.bar.com, you will 
 find the nameserver looks up the foo.bar.com as a canonical name in 
 the zone file you set in the first time, but it will finally find out 
 the domain name is a alias of domain name bar.com. So the nameserver 
 will reset the query for asking the corresponding IP address for bar.com.
 It is also meaning that the relation is 
  "foo.bar.com -> bar.com -> 37.124.19.7". 
                    
 About the detail of how the nameserver works, maybe you can refer the 
 RFC1034, DOMAIN NAMES - CONCEPTS AND FACILITIES.

SHI