option 51 ' dhcp-lease-time' vs other lease time statements

David W. Hankins David_Hankins at isc.org
Tue Sep 19 16:49:03 UTC 2006

On Tue, Sep 19, 2006 at 10:46:41AM -0400, Aaron Bennett wrote:
> What's the difference?  What exactly does option 51 do and how does that 
> compare to the other ways to specify a lease time?  What I'm looking for 
> is the migrate the exact _intent_ of the Win2K configuration 
> intelligently into isc-world.

In dhcpd.conf, 'option dhcp-lease-time foo;' will be over-ridden by
a value selected by the server.  So it will have no effect except to
cause a logline warning about the over-ride.

If the client supplies option 51, the server selects a value close to
the client-supplied value that falls between the min- and max-lease-time
config options.

If the client does not supply option 51, the server does the same thing
except uses the default-lease-time (so it's a good idea to choose a
default that is somewhere inside your min/max range).

If you're using failover, a second layer of complexity is added.

> ( I'll contribute the script back to isc when it's done -- finished 
> product will handle both config & lease database )

dhcp-suggest at isc.org please.

ISC Training!  October 16-20, 2006, in the San Francisco Bay Area,
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David W. Hankins	"If you don't do it right the first time,
Software Engineer		you'll just have to do it again."
Internet Systems Consortium, Inc.	-- Jack T. Hankins

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