how to force new leases (not renewals)

Simon Hobson dhcp1 at thehobsons.co.uk
Tue Jan 26 08:07:13 UTC 2010


Justin DeMaris wrote:
>One very unconventional trick we have used to push out lease changes 
>is to do shut/no shut on the switch port interface. This only works 
>for devices wired directly to the switch with no active 
>amplification (hub, etc) in between but it makes windows and linux 
>do a full new lease since it feels like it got unplugged

Does it still do that ? Some modern clients do tricks like checking 
if the MAC address of the default router is still the same to 
determine if they are on the same network after bringing up an 
interface.

Back to the original issue, I'm sure it's been reported before - 
WIndows clients changing their address but not recognising any 
changed options.

If the OP has enough address space then they could simply move the 
range completely (overnight or at another quiet time) which would 
force all clients to get a new address. Also, either in conjunction 
with that or on it's own, progressively reduce lease times so that 
all clients will expire their leases overnight. Thinking about it, if 
you don't mind a complete outage for a few minutes at a quiet time, 
get the lease length down to (say) 5 minutes, then shut down the DHCP 
service for 5 minute - that is guaranteed to make all leases expire 
even if a client is up permanently.

-- 
Simon Hobson

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