Best practice on removing IP Scopes(subnets)

Christof Chen christof at
Fri Apr 24 15:34:26 UTC 2009

Simon Hobson schrieb:
> If you can't (or don't want to) do parallel running at all, then you
> will want to get clients onto really short leases. Reduce lease times in
> advance - eg gradually cut them down
> 4wk-2wk-1wk-4day-2day-1day-12hr-3hr-... Ie, at t-4weeks, cut the lease
> time down to 2 weeks, at t-2weeks, cut the lease time down to 1week and
> so on. Just remember that the shorter you get the lease times, the
> quicker your customers will notice if your server breaks !
> At the appointed time, change configs - router interface addresses and
> DHCP server. Clients will lose connectivity until they lease a new
> address, but if your lease times are short, then this should be too much
> of a problem if you time it right AND inform customers accordingly. In a
> corporate environment I'd plan to do this when the lease number of
> people are on the systems - which will obviously depend on your shift
> patterns and countries served.

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.

Best regards,
	Christof Chen

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