Classless PTR query issue

Justin T Pryzby justinpryzby at
Tue May 7 18:10:44 UTC 2013

On Tue, May 07, 2013 at 09:52:16AM -0700, Michael Varre wrote:
> Thanks Justin, I've been testing with dig and that's how I got the failed results posted previously. My digs lead me to believe their zones are named the same as mine, with -'s instead of /'s. 
> dig -x +trace
> ----snipped----
> ;; Received 180 bytes from in 89 ms
> 86400  IN      NS      NS1.myisp.COM.
> 86400  IN      NS      NS2.myisp.COM.
> ;; Received 89 bytes from in 55 ms
> 3600 IN     NS
> ;; Received 75 bytes from in 84 ms
> ;; Received 44 bytes from in 80 ms
> <end>
> I've requested they confirm their setup, but I don't know how forthcoming they'll be.

I don't see any "-" (or "/") in your dig output, which indicates that
the ISP delegation isn't using RFC2317-style delegation with CNAMES.

It appears they may have manually added NS records for each of 64 IPs.
That's messy and inelegant for them, and doesn't work right either.
The ISP is responding with NS for, which means that the next
query must ask a quesion *below* that: something.  That's why
a CNAME is needed, with an additional, "artificial" subzone, allowing
proper delegation.  Otherwise, it's a so-called "horizontal" referal.

In the past, when I've requested RFC2317/sub-24 delegation of rev dns,
I've included/suggested BIND syntax (but it's still sometimes taken
multiple attempts to be correctly implemented).

32-47 NS
32-47 NS
$GENERATE 32-47 $ CNAME $.32-47


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