moving subnet to another server

Michael Ströder michael at
Fri Jan 9 19:43:11 UTC 2015

Dana Huggard wrote:
> Thanks Patrick.   I don't know how to handle that. Not sure how smart dhcp
> is to detect such a condition or how long it would take for things to sort
> itself out.

I don't consider myself to be a DHCP expert. But this is not something to be
explained with a few words in a mailing list posting to get successfully done
with this task.

What exactly do you want to achieve?
Why are you migrating to a new server?
Just for better performance?
How many subnets do you have?
How big are they?
How many active leases?
Do you need real HA with DHCP failover server?

Seriously, you should get a good DHCP book and read about all this, e.g. "The
DHCP handbook" by Ralph Droms and Ted Lemon.

> The default-lease-time in the subnet declaration is 600.   Is there a
> preferred way to handle this?

This is very short. Now wonder that your DHCP server is under heavy load. The
DHCP clients have to ask for lease renewal after 300s then.

Read chapter "Tuning a DHCP Service" in the book mentioned above to learn how
to choose appropriate min/default/max lease-times before doing anything else.

Ciao, Michael.

> On Fri, Jan 9, 2015 at 10:59 AM, Patrick Trapp <ptrapp at> wrote:
>>  How are you planning to prevent the new server from handing out
>> addresses already assigned by the old server?
>>  ------------------------------
>> *From:* dhcp-users-bounces at [dhcp-users-bounces at]
>> on behalf of Dana Huggard [dana.huggard at]
>> *Sent:* Friday, January 09, 2015 12:33 PM
>> *To:* dhcp-users at
>> *Subject:* moving subnet to another server
>>   Hi.
>>  I'm planning on moving a subnet over to another server and am not sure
>> what kind of devil hides in the details.
>>  The subnet is 10.x.x.0/18 and it is very busy. Its a subnet devoted to a
>> test harness of servers that go up and down a lot putting a big load on
>> dhcpd and named (using ddns).
>>  Along with the dhcpd change the new dhcp server will also serve as a dns
>> server for a new domain.
>>  To implement the move I have a new dhcp server I plan to remove the
>> subnet declaration from dhcpd.conf off the old server, add it to the new
>> server, then restart dhcpd on the old server, and start dhcpd on the new
>> server.
>>  What I am wondering about is what to expect for the behaviour of the
>> dhcp clients. How disruptive might this be?
>>  Thank you.

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