Subnet, Pool, and Zone Declarations

Merton Campbell Crockett m.c.crockett at
Wed Nov 25 06:00:18 UTC 2009

Sorry for not responding sooner but one of the problems with being an "old fart" who started working with computers in the Sixties is that your experience is invaluable in investigating problems, i.e. you came from the time before specialization became rampant.

The only DHCP declarations that are, absolutely, global in nature are "authoritative" and "host".  The other DHCP declarations that appear to be global in nature are "class", "group", and "shared-network".  All other declarations can appear within the scope of these global entities or as global entities in and of themselves.

A "zone" declaration is not a global entity.  It can be defined globally but can be defined or redefined within a scope.  IPAM systems shouldn't assume that a "zone" declaration only occurs within a global context.  If they do, they should declare that this is a restriction of their implementation.


On 09 Nov 2009, at 15:27:00, Chris Buxton wrote:

> The documentation of the syntax of dhcpd.conf seems to be quite thin and vague, depending more on examples than reference data. Therefore, if the syntax you have used works, then it's probably correct - or at least there's no definitive way to disprove it.
> However, as a member of the team supporting an IPAM solution such as you describe, I can say that our development team has had a very difficult time trying to accommodate all possible combinations of statements in dhcpd.conf. Therefore I'm not surprised that your vendor's product has trouble with the syntax you've used - nowhere in the dhcpd.conf manpage does it say that it is valid to declare a zone inside another declaration.
> Chris Buxton
> Professional Services
> Men & Mice
> On Nov 7, 2009, at 9:30 AM, Merton Campbell Crockett wrote:
>> Can a zone declaration appear within a pool or subnet declaration?
>> My company acquired an IP Address Management (IPAM) system.  One of its features is that it provides a place to store information about a system that, normally, would not be in a DNS zone file.  Another is that it provides a safe way to allow server administrators and site support personnel to make DNS changes.  Another feature is that it allows IT and Security personnel to see the DHCP lease assignments and identify which IP addresses are currently leased and by what systems.
>> My question involves this last feature.  At several sites, I have included a zone declaration inside a subnet or pool declaration.  The rationale for doing this was that the zones were unique and only to be used for systems that were leased addresses from the subnet or pool.  DHCP 3.1.2p1 accepts this construct.
>> The vendor of the IPAM system has done a relatively good job of ensuring that the IPAM system conforms to DNS and DHCP standards; however, it won't process DHCP lease information when there is a zone declaration within a subnet or pool declaration.
>> Is my usage of zone declaration within a subnet or pool declaration valid?  Does the vendor of the IPAM system have a "bug" in its implementation that needs to be corrected?

Merton Campbell Crockett
m.c.crockett at

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