Parent is a CNAME

[Chris Buxton]

On Dec 1, 2009, at 7:50 PM, Joseph S D Yao wrote:
> On Tue, Dec 01, 2009 at 04:59:16PM -0800, Hans Jacobsen wrote:
>> If a.stanford.edu is a cname (say to b.stanford.edu)
>> can I delegate subdomain.a.stanford.edu?  Are there documents that  
>> point to this being an ok or bad practice?
>> 
>> I know all records for a.stanford.edu are relegated to records for  
>> b.stanford.edu
>> What about subdomains?
> 
> 
> No.
> 
> The domain that has a CNAME must never appear on the left-hand side of
> another record.
> 
> If you delegate, the domain appears on the left side of NS records.

That is incorrect. The child of the alias does not equal the alias.

The following is absolutely correct:

a	CNAME	b
sub.a	NS	some.host.

Just to be sure, I tested it before composing this message.

Joseph, I used to have the same misconception as you, that an alias couldn't have children (subdomains) of its own. Someone on this very list sorted it out for me, years ago, with a working example that looked roughly like this:

gw	CNAME	a.gw
a.gw	A	192.0.2.1
b.gw	A	192.0.2.2
c.gw	A	192.0.2.3

The purpose of this was to enumerate all of the available routers, as {a,b,c}.gw, and then have the currently active router referenced as simply gw. The solution used involved an alias name that had three children.

Chris Buxton
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