DHCP lease order

Simon Hobson dhcp1 at thehobsons.co.uk
Fri Jan 23 20:20:16 UTC 2009

Brendan Forsyth wrote:
>Our dhcp server gives out leases from the end of the subnet back to 
>the beginning.
>Is it possible to reverse this ordering?

Actually, the ISC server allocates (never used before) addresses in 
an implementation specific and undocumented order - it just so 
happens that AT THE MOMENT it does it "top down".

That is only the case when there are addresses that have never been 
used. Once there are no such addresses, it will reclaim expired 
leases in a least recently used manner and normally addresses will 
then appear to be allocated randomly.

There is no direct way to influence allocation order of addresses, 
but you can fudge the issue if you really care (why ?). If you write 
a script that will create dummy leases for all available addresses, 
then you can determine the order that addresses will be allocated in 
future by simply ordering the expiry date/time of each dummy lease.

The obvious question is why do you want a specific order ? There 
isn't really any good reason other than your are trying to do 
something that probably has a another way.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
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