DNS reverse addresses (was re: reading IP addresses given via DHCP)

Dan Egli ddavidegli at gmail.com
Thu Oct 3 03:04:47 MDT 2013

On Sept. 27, 2013, Lonnie Olson wrote:

> There is nothing wrong with just having one reverse zone for

> 168.192.in-addr.arpa. I highly doubt you would need to query for

> those records anyway. ;) Also, your actual subnet size does

> not have to match the size of the DNS zone. They can be unrelated.

Sorry on the delay replying, I couldn't get online for a couple days. So,
what you're saying is that ISC's DHCPd would let me have a single ddns
update key for all three zones (upper.rec, lower.rec, and in-addr.arpa) and
it would update the appropriate zone accordingly? That's interesting, and
was not what I had understood. Or maybe it would be two keys? Where zone
"upper.rec" gets key #1, zone "lower.rec" gets key #2, and the in-addr.arpa
gets keys one AND two? Before I make any changes in that direction, can you
please confirm this? If it would work, then that's really going to save
some time and complexity, not to mention needing to restart bind (I would
still need to restart dhcpd though, so that it sees the declaration of the
reserved IP for that machine after it's initial self configuration).

The point of updating the in-addr.arpa records is that my understanding
says the in-addr.arpa zone is queried when, for example, you do a netstat.
Then any connections to the machine (unless you specifically add the flag
not to resolve names) generate calls to in-addr.arpa to confirm that (for
example) is moe.upper.rec and is
peitre.lower.rec. Now, if that's not the case, then I'm all ears. But that
was my understanding of how names were resolved in such circumstances.

The PXE config is already as simple as I could possibly make it without
regenerating the pxelinux.0 file to make multiple boot-loader images. And
even then I'd have to pass it some kind of config file or related, wouldn't

I'm not sure what you mean by infinite leases in DHCP. I was under the
impression that DHCP leases were finite. After all, there ARE two
parameters in the config file that specify the average lease time and the
maximum lease time. Would I just specify those as 0 or something to make
them infinite? And wouldn't infinite leases cause an issue when replacing
boxes? I'd think an infinite lease would thus isolate that address forever,
and the only way to recover it would be to manually edit the leases file
and remove that lease.

I actually do have some automatic hostname assignments on lower.rec. I just
didn't mention that (my bad). It's only on the smaller upper.rec zone that
it asks for a hostname during setup. The lower.rec simply reads from a list
on the server that says, for example, is austin.lower.rec, is miller.lower.rec, etc...

Thanks for the help on this!

--- Dan

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