Static IP and IP management

Patrick Trapp ptrapp at
Wed Feb 24 14:55:23 UTC 2016

Much clearer, thanks. Disclaimer: I'm far from the most experienced DHCP person haunting this list, so I'm sure there are options I'm not aware of. Some thoughts, in no particular order:

Since you say you can look in dhcpd.conf to see what addresses are assigned, I have to ask: Are you using "static" addresses in dhcpd.conf to assign an address to a given MAC address?

Is this a single flat network where everything can reach everything or do you have it segmented for various tests?

Is the issue knowing which addresses are available or just knowing how many addresses are available?

If you are using host entries to dictate what address a device gets (and not allowing devices to grab random addresses - effectively making them static without having to configure it on the device), then when you delete that host entry from the dhcpd.conf, you would know that address is free.

I'm not sure if that's what you are doing or if that's what your advisor had in mind. Depending on how often equipment comes in and goes out, that could become pretty tedious, but you would have that control/knowledge in return.

I have include files on my server that are assigned to a particular type of device that I manage. Within each include file, the host entries are sorted as I enter them so the data is organized. If I was doing this for a lab, I might (this is off the cuff and untested) allocate an include file for a particular subset of addresses (not knowing what you are testing, I don't know what would be a reasonable scope). Then I would use that include file for all devices on a particular test. When the test is complete, I clear the file and I know those addresses are available for the next test. Obviously not foolproof, but it might be an idea you could build on.


From: dhcp-users-bounces at [dhcp-users-bounces at] on behalf of Bernard Fay [bernard.fay at]
Sent: Wednesday, February 24, 2016 8:16 AM
To: Users of ISC DHCP
Subject: Re: Static IP and IP management

I manage a lab where there is about 300-400 IPs assigned to different network equipments, physical and virtual servers.  So IPs might be assigned for a while then equipments removed because not needed anymore, remember this is a lab.  I would like to know which IPs are in used or not.  Equipments removed means IPs not used anymore so we could reuse those IPs.

I hope I am clear enough

On Wed, Feb 24, 2016 at 9:06 AM, Patrick Trapp <ptrapp at<mailto:ptrapp at>> wrote:
I believe a helpful answer will require some context. You haven't told us what issues you are having with IP management, so it's going to be difficult to identify how static IP's might be beneficial.

Are you having a specific issue you wish to address?

From: dhcp-users-bounces at<mailto:dhcp-users-bounces at> [dhcp-users-bounces at<mailto:dhcp-users-bounces at>] on behalf of Bernard Fay [bernard.fay at<mailto:bernard.fay at>]
Sent: Wednesday, February 24, 2016 7:39 AM
To: Users of ISC DHCP
Subject: Static IP and IP management

Hello everyone,

I have been told that static IP assignation can help in IP management.  Of course, I can know which IPs are assigned by looking in dhcpd.conf.  But after a while an IP might not be used anymore and nothing in dhcpd or bind will tell me if it still in use or not.  I have setup a lab to experiment where I have configured dhcpd and bind and I cannot find out how static IP can really help in IP management.

Did I miss something somewhere?


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