reading IP addresses given via DHCP

Lonnie Olson lists at
Fri Sep 27 09:25:07 MDT 2013

On Fri, Sep 27, 2013 at 5:39 AM, Dan Egli <ddavidegli at> wrote:
> On Sept. 25, 2013, at 10:23 PM, Lonnie Olsen wrote:
> Believe me, I have. Unless my understanding of the dynamic update
> functionality of ddns is wrong, it won't quite do what I was looking for.
> Maybe I'm wrong. If so, please tell me, and preferably show me an example
> somewhere that shows the implementation, but my understanding of ddns is
> that it wouldn't quite work for this instance. See, the problem is that the
> different IP ranges for the different physical locations are different SIZES
> (one is a simple class C, the other is a subnet'ed class B). Therefore, the
> only way I could maintain the reverse pointers was to either define one
> zone for the whole 192.168.X.Y class B subnet, or to define
> multiple Class C zones. Now my understanding (and again, this
> could be wrong, so if it is please tell me!) is that DHCPd's ddns updates
> can't do that. If it even supports updating the PTR records at
> all (which I can't tell if that is doable or not), it's going to expect one
> security key per zone. That would be fine if I had, for example, zone
> upper.rec (bogus name, but gets the idea across) in the file, and
> had a ddns update key for it and it's zone, then another for
> lower.rec and it's zone. The problem is that in this instance I
> either have one zone for upper AND lower, or I have multiple
> zone files for lower since lower is the subnet'ed class B range.

There is nothing wrong with just having one reverse zone for  I highly doubt you would need to query for
those records upstream anyway.  ;)  Also, your actual subnet size does
not have to match the size of the DNS zone.  They can be unrelated.

Here are some options that may streamline your processes:

* Since you choose your PXE config based on subnet alone, put this
definition into DHCP.  Serve up a different config per subnet.  You
may need to run two instances of tftp on different IPs to serve two
different roots.  This keeps the symlink nightmare more dynamic and
makes moving machines easy.

* Yes DHCP ddns updates the reverse too if possible.

* Set your lease length to infinite to avoid the requirement to set
static leases by script.

* Pre-populate DNS with hostnames per IP, so the hostname assignment
is dynamic instead of requiring a user intervention.

More information about the PLUG mailing list