Order that ranges are dolled out?

Keith Lawson Keith.Lawson at sjhc.london.on.ca
Wed Mar 7 18:20:16 UTC 2007

>>> On Fri, Mar 2, 2007 at  3:03 PM, in message
<a06230900c20e322da4e7@[]>, Simon Hobson <dhcp1 at thehobsons.co.uk>
> Carl Karsten wrote:
>>  > I'm sure this has been asked here before but I can't seem to find 
>>anything in the archives.
>>>  When dhcpd dolls out leases from a range does it do it in 
>>>numerical order starting at the lowest number and going up until it 
>>>finds the next available IP?
>>Hate to be trite (whatever that means) but why would you care?
>>Whatever problem you are trying to solve probably has a better solution than
>>relying on IP order.
> Funnily enough, exactly the first thing that came to mind when I read 
> the question.

One of our network admins asked me the question and I didn't have a definite answer for him. He didn't explain to me why he wanted to know. If there is an existing problem I'll address it properly.

> As has been mentioned, this ONLY happens while there are unused 
> addresses available, and after that addresses are handed out in a 
> non- deterministic manner as seen from an outside observer without 
> knowledge of the contents of the leases file.
> There is another complication as well, though it won't affect many 
> installations. If you have an existing DHCP server, switch it off, 
> and replace it with the ISC server -  then many clients will get the 
> address they are already using and NOT the next in sequence. This 
> will happen when the clients request an extension of their existing 
> lease, at which point they will get it if it is an available address 
> under the new config.
> It probably also applies to clients (such as Windows IIRC) that 
> retain their lease info and specifically ask for the same address 
> next time they bring up their interface.

Thanks for the detailed responses. 

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