Chaining CNAMEs?

[Barry Margolin]

In article <ecdm8l$274b$1 at sf1.isc.org>,
 Chris De Young <chd at arizona.edu> wrote:

> Hi,
> I was just browsing through the latest edition of the O'Reilly
> DNS/BIND book, and ran across a bit on pointing a CNAME record at
> another alias:
> 
> "The answer is yes: you can chain together CNAME records. The BIND
> implementation supports it, and the RFCs don't expressly forbid it."
> 
> The authors go on to recommend against it anyway, but I had always
> thought that this was actually illegal.  I don't remember now where I
> had gotten that idea... I think the issue had to do with not being
> guaranteed that the server would always do the additional processing
> to ensure that you got to the canonical name at the end of the chain.
> 
> I guess I've been mistaken?  :-)

Yes, you have been.  Note, however, that you can't take it too far.  To 
prevent loops, servers usually have a limit on the number of times 
they'll restart a query.  And since it's not common to have long chains 
of CNAMEs, the limit is typically pretty low, like 5-10, and most of 
this can be taken up by having to resolve NS records in delegations.

-- 
Barry Margolin, barmar at alum.mit.edu
Arlington, MA
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