Best practice on removing IP Scopes(subnets)

Christof Chen christof at
Fri Apr 24 17:12:54 UTC 2009

John Hascall schrieb:
> Christof Chen writes:
>> I just want to mention there is a fairly recent addition to DHCPD:
>>     deny after TIME;
>> in a pool shortens the lease duration automatically as TIME approaches.
>> Together with a corresponding
>>     allow after TIME;
>> in a different pool this allows for a nearly automatic switchover at a
>> preconfigured time.
> That's pretty swell, but what would really be awesome is
> something which would allow renews, but not new offers
> in a pool!
> Maybe allowing "deny booting" in pool scope could do that.
> Then you could very nicely switch from one pool to another.
> John

It depends on what you want to achive: The idea behind the current
implementation was that if you know you will be doing maintenance on a
certain subnet beginning tonight at 3:30 (making it unusable for
routing), it isn't nice to give the customer an IP valid for e.g. one
hour at 2:25...
"deny after" assures you that the subnet is empty after the stated time
plus min-lease-time.
In conjuction with "allow after" you can be sure that all clients have
transitioned to a new pool _without_ manually reducing lease times
several times and restarting dhcpd.

Christof Chen

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