Order that ranges are dolled out?

Simon Hobson dhcp1 at thehobsons.co.uk
Fri Mar 2 20:03:05 UTC 2007

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.

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.

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