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Re: New Internet Draft on registering IDNs



Martin Duerst <duerst@xxxxxx> wrote:

> CNAME or DNAME?

CNAME and DNAME mean different things.  CNAME defines an alias for a
particular name (the alias is a leaf in the tree).  DNAME defines an
alias for a domain suffix (the alias effectively creates a mirror of a
whole subtree).  Paul's draft describes three different methods to get
www.foo.example.com and www.bar.example.com to refer to the same server:

parallel delegations and resource records:

    example.com zone:
        foo.example.com. NS <nameserver>
        bar.example.com. NS <nameserver>
    foo.example.com zone:
        www.foo.example.com. A 1.2.3.4
    bar.example.com zone:
        www.bar.example.com. A 1.2.3.4

parallel delegations with CNAME:

    example.com zone:
        foo.example.com. NS <nameserver>
        bar.example.com. NS <nameserver>
    foo.example.com zone:
        www.foo.example.com. A 1.2.3.4
    bar.example.com zone:
        www.bar.example.com. CNAME www.foo.example.com

single delegation with DNAME:

    example.com zone:
        foo.example.com. NS <nameserver>
        bar.example.com. DNAME foo.example.com.
    foo.example.com zone:
        www.foo.example.com. A 1.2.3.4

The last method is the simplest, because there is no bar zone to manage.
On the other hand, it's less flexible--the manager of the foo zone
no longer has the ability to cause www.bar.example.com to refer to a
distinct server, except by asking the manager of example.com to change
the DNAME to an NS.

Hmmm, is there a fourth method?

parallel delegations with DNAME:

    example.com zone:
        foo.example.com. NS <nameserver>
        bar.example.com. NS <nameserver>
    foo.example.com zone:
        www.foo.example.com. A 1.2.3.4
    bar.example.com zone:
        bar.example.com. DNAME foo.example.com

Is that allowed?  This way the foo manager wouldn't need to update the
bar zone whenever a new host gets added to the foo zone, and would still
have the power to fork off the bar.example.com domain without having to
wait for updates in the example.com zone.

AMC