Glue for exporting DHCP provisioning into Bind
marka at isc.org
Thu Jun 14 05:48:11 UTC 2018
> On 14 Jun 2018, at 4:15 am, Philip Prindeville <philipp_subx at redfish-solutions.com> wrote:
> My last message didn’t get any replies so let me try a more tangible question.
> I’m looking at this article:
> in particular the example.
> From the subnet 198.51.100.0/26 for a host they get the following RR’s:
> 18.104.22.168.in-addr.arpa. 86400 IN CNAME 1.0/22.214.171.124.in-addr.arpa.
> 1.0/126.96.36.199.in-addr.arpa. 86400 IN PTR my.machine.example.
> Dumb question… they end up with 5 octets before they add the suffix on and reverse the order:
> How are they deriving those last 2 digits? The 198.51.100 is obvious… that’s 26 rounded down to the nearest multiple of 8 (/24) and taking that many net digits… the /26 is of course the prefix. 0 would be the network start, I guess? Since it’s a /26 prefix, subtracted from 32, that’s 6… 2^6 is 64, so there would be 0, 64, 128, and 256 as subnet starts… And I’m guessing that 1 module 64 is 1… and that’s how they get the 1 digit?
The 1 comes from the last octet of the IP address.
If it was for 188.8.131.52/26 then the records would look like:
184.108.40.206.in-addr.arpa. 86400 IN CNAME 65.64/220.127.116.11.in-addr.arpa. (in 100.51.198.in-addr.arpa.)
65.64/18.104.22.168.in-addr.arpa. IN PTR my.machine.example. (in 64/22.214.171.124.in-addr.arpa.)
> What if the prefix were /22?
You delegate the 4 reverses for the /24’s that make up the /22 without applying the techniques in RFC 2317.
RFC 2317’s target prefixes lengths are /32-/25. The intent is to not have to delegate a reverse zone for
each IP address in the range.
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Mark Andrews, ISC
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