Chaining CNAMEs?

[Mark Andrews]

> 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?  :-)

	RFC 1034:

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.

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