Re: [exim] Subtle delivery issue - BROKEN DNS PTR questions.

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Author: Todd Lyons
CC: exim-users
Subject: Re: [exim] Subtle delivery issue - BROKEN DNS PTR questions.
On Tue, Apr 3, 2012 at 7:51 AM, <> wrote:
>> > The host concerned has a PTR record, it's a bit of a mess, but it's
>> > there:
>> > dig -x
>> >
>> > 17019 IN  CNAME
>> >
>> > 65020 IN PTR
>> >
>> SOP for doing rDNS for non 8 bit boundaries.
> I'm sorry Todd, I don't understand that?

SOP means Standard Operating Practice, sorry if the acronym didn't
translate well.

When delegating reverse dns to a company, say for example our assignment, the registrar can very simply point to our nameservers because it's on an 8 bit
boundary. However, what if we only had
( and *you* had
( Those are not on an 8 bit boundary.
The registrar cannot give the entire reverse
delegation to us, nor to you (because that would omit the other from
being able to do reverse dns). So you break it up by inserting an
extra octet using either START-END or START/NETMASK. Your buddy's
registrar uses the START-END method.

We also have, and our ISP delegates it to us with
START/NETMASK method: 3600 IN    CNAME    119.112/
112/    3600 IN    NS
112/    3600 IN    NS
;; Received 116 bytes from in 1 ms

Then when your resolver chases that 112/
delegation, it gets the following result from our nameservers:
;; ANSWER SECTION: 2958 IN    CNAME    119.112/
119.112/ 8380 IN PTR

Always code as if the guy who ends up maintaining your code will be a
violent psychopath who knows where you live. -- Martin Golding