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Re: [DNSOP] CNAME chain length limits

Evan Hunt <each@isc.org> Wed, 27 May 2020 18:08 UTC

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Date: Wed, 27 May 2020 18:08:46 +0000
From: Evan Hunt <each@isc.org>
To: John R Levine <johnl@taugh.com>
Cc: dnsop@ietf.org
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Subject: Re: [DNSOP] CNAME chain length limits
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On Wed, May 27, 2020 at 01:48:32PM -0400, John R Levine wrote:
> is there any consensus as to the maximum CNAME chain length
> that works reliably, and what happens if the chain is too long? Hanging
> seems sub-optimal.

BIND cuts CNAME chains off at 16. As far as I know that was an arbitrarily-
selected value, but it's been in the code since 1999 and so far as I can
recall, no one's complained. The maximum reliable chain length won't be any
longer than that; it might be shorter.

When a chain is too long, I think BIND just returns a response with the 16
CNAMEs it's found so far, and without a final answer. The client can start a
new query from where the response left off, but I would expect most to
treat it as a non-answer.

-- 
Evan Hunt -- each@isc.org
Internet Systems Consortium, Inc.

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