Define a domains addresses sole in terms of another

[Stephane Bortzmeyer]

On Mon, Jul 09, 2007 at 08:48:00PM -0400,
 Barry Margolin <barmar at alum.mit.edu> wrote 
 a message of 46 lines which said:

> The RFC recommends against it for performance reasons, but doesn't
> prohibit it.

Yes, it does.

RFC 1034, 3.6.2 "Aliases and canonical names" :

> Domain names in RRs which point at another name should always point at
> the primary name and not the alias.  This avoids extra indirections in
> accessing information.  For example, the address to name RR for the
> above host should be:
>
>    52.0.0.10.IN-ADDR.ARPA  IN      PTR     C.ISI.EDU
>
> rather than pointing at USC-ISIC.ARPA.  Of course, by the robustness
> principle, domain software should not fail when presented with CNAME
> chains or loops; CNAME chains should be followed and CNAME loops
> signalled as an error.

BIND follows the advice, it works with CNAME chains. Not all resolvers do.

> It even mentions that resolvers must follow CNAME chains,

Not "must", "should".