dhcpd issue static lease on first request

Simon Hobson dhcp1 at thehobsons.co.uk
Tue Oct 26 07:14:55 UTC 2010

Christ Schlacta wrote:

>I've just noticed that over time the systems gradually start to 
>change IP.  one day my laptop will have .235, and it'll have that IP 
>for months, then suddenly it's 166, and I'm liek wtf?  there are 
>only about 20-30 systems on the network, (depends on whether you 
>count dual boots as two from a dhcp perspective), so it's not an 
>exhaustion thing.  I've reserved from 130-250 for dhcp.

That shouldn't happen, When IPs have all been used once, recently 
active devices should be the last to have their addresses reused. It 
may be worth looking for any BOOTP leases as these are infinite by 
default and can tie up addresses forever until you manually clean 
them out - and the same applies to leases marked abandoned. At my 
last job we would occasionally have problems with Macs (OS 9) 
refusing to take an address - and I fixed that by setting them to 
manual and back to automatic which seemed to cure it. A colleague 
would set them to BOOTP and back - not knowing that each time he did 
this, it permanently tied up an address.

Something else that will cause an address change is if there is ANY 
change in client-id. Client-id is the primary key for the lease 
database and if it changes then your machine is a different device as 
far as the server is concerned.

Lastly, as an alternative to what's been suggested before, you could 
set the reserved flag on a lease if you are running a current 
version. The lease still goes through the same lifecycle, but will 
never be given to another device - it's permanently allocated to your 
MAC address.

There is the other question though - why does it matter ? If you are 
using dynamic DNS, then you will get the relevant DNS updates and 
still be able to refer to your machine by DNS name.

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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