Glue for exporting DHCP provisioning into Bind

[Philip Prindeville]

My last message didn’t get any replies so let me try a more tangible question.

I’m looking at this article:

https://www.freeipa.org/page/Howto/DNS_classless_IN-ADDR.ARPA_delegation

in particular the example.

From the subnet 198.51.100.0/26 for a host they get the following RR’s:

1.100.51.198.in-addr.arpa. 86400 IN	CNAME	1.0/26.100.51.198.in-addr.arpa.
1.0/26.100.51.198.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:

198.51.100.0.1

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?

What if the prefix were /22?

Thanks,

-Philip