Re: [DNSOP] RFC2317 Question: Resolving cname delegation

P Vix <> Thu, 24 August 2017 17:07 UTC

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Date: Thu, 24 Aug 2017 17:07:18 +0000
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To:, Hector Santos <>, "" <>
From: P Vix <>
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Subject: Re: [DNSOP] RFC2317 Question: Resolving cname delegation
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This is why rfc 2308 definition of qname is correct.

On August 24, 2017 9:46:58 AM MDT, Hector Santos <> wrote:
>I have a question related to RFC2317 "Classless IN-ADDR.ARPA
>Earlier this year, I switched from a class C bank of 256 addresses to 
>a reduced  set of 32 ips (/27).  To get PTR queries to work, RFC2317 
>was referred by my ISP to prepare the delegation.
>Having implemented RFC2317, I noticed with PTR lookups directly 
>against my own DNS server, it returns the proper host names, no 
>cnames.   When the query is done against other DNS servers, it returns 
>the CNAME which points to the expected host name(s).  This I 
>understand is the expected RFC2317 method setup by the ISP.
>Not expecting this in my DNS resolver code, I modified the resolver to 
>take the CNAMEs into account and return the host names instead.  Was 
>this the correct thing to do, thus providing the same results 
>regardless of the query location?
>Reading RFC2317, section 5.1 and section 5.3, it sounds what I did was 
>I have various PTR lookup scripts that did not expect the CNAME in the 
>PTR query as RFC2317 indicates may happen, thus possibly failing a PTR 
>requirement, i.e. SMTP receiver connection, etc.
>Before I release my updates, I wonder if this was the right thing to
>DNSOP mailing list

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