Excluding a range from a subnet

Randall C Grimshaw rgrimsha at syr.edu
Wed Apr 23 13:26:20 UTC 2008

That is how I understand it.
I will recommend that you build some form of IP management database, and then essentially build the dhcpd.conf file from that. A database will help you track the reserved addresses over time.


-----Original Message-----
From: dhcp-users-bounce at isc.org [mailto:dhcp-users-bounce at isc.org] On Behalf Of Olivier Bax de Keating
Sent: Wednesday, April 23, 2008 9:02 AM
To: dhcp-users at isc.org
Subject: RE: Excluding a range from a subnet 

Just to be sure,

If I declare a host, with an ip and a mac address, the ip won't be reserved, that means, if in a subnet I declare a range containing that ip, it may be attributed dynamically? I would have to segment my ranges as in your example to be sure that my server won't propose this "reserved ip".

Thanks for all


-----Message d'origine-----
De : dhcp-users-bounce at isc.org [mailto:dhcp-users-bounce at isc.org] De la part de John Hascall
Envoyé : mercredi 23 avril 2008 13:35
À : dhcp-users at isc.org
Objet : Re: Excluding a range from a subnet 

> I have to add a dhcp server in an already configured subnet, and manage
> a range. The problem is that in my range, there may be one or many
> devices with a static ip not configured in dhcp, and my dhcp server
> musn't manage them. I'd like to declare one range, with excluded
> ip/ranges to ignore. I had a look on internet but didn't find smthg
> corresponding exactly to what I need :

[manually abandon the addresses in the lease file]

  This will surely bite you some day in the future.

> Segmenting my range :

   This is what you need to do.
   It is not that hard or inelegant.  For example:

	shared-network "sample" {
		subnet netmask {
			option broadcast-address;
			option routers;
		# we always reserve 0, 250-255
		# 15, 42-49, 51-56, 61 are not managed by dhcp
		pool {

> Declaring them as hosts :

   Given a new enough version of dhcpd you can apparently 'reserve'
   the in use addresses in th erange to the existing devices.  I
   have not tried this myself.


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