Glue for exporting DHCP provisioning into Bind

Philip Prindeville philipp_subx at
Wed Jun 13 18:15:53 UTC 2018

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 for a host they get the following RR’s: 86400 IN	CNAME	1.0/
1.0/	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?

What if the prefix were /22?



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