Static IP and IP management

Bernard Fay bernard.fay at
Wed Feb 24 18:06:07 UTC 2016

Check my answers in caps below....

On Wed, Feb 24, 2016 at 9:55 AM, Patrick Trapp <ptrapp at> wrote:

> 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?  YES STATIC WITH MAC ADDRESSES
> Is this a single flat network where everything can reach everything or do
> you have it segmented for various tests?  YES SEGMENTED WITH MANY VLANs
> Is the issue knowing which addresses are available or just knowing how
> many addresses are available?  WHICH ADDRESSES SO THEY CAN BE REASSIGNED IF
> 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
> 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.
> Patrick
> ------------------------------
> *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
> Thanks,
> On Wed, Feb 24, 2016 at 9:06 AM, Patrick Trapp <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 [
>> dhcp-users-bounces at] on behalf of Bernard Fay [
>> 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?
>> Thanks,
>> B
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