David W. Hankins David_Hankins at
Mon May 1 17:33:12 UTC 2006

On Mon, May 01, 2006 at 10:59:24AM -0400, Mike Diggins wrote:
> Would you recommend this option for a Student Residence with multiple 
> subnets? I want to be sure we're not wasting addresses.

Personally I'd prefer shorter lease-times for those situations.

one-lease-per-client is a violation of the protocol that has, in practice,
not caused problems...due to how we know DHCP client implementations to
be written.  They generally only bind to the most recently allocated
address (if they bind to an address at all) at startup.

That may be changing however particularly as in the present day, as
compared to years past, DHCP clients are much more mobile than they
used to be.

See also RFC 4436.

I think we're going to start seeing changes in DHCP client implementation
if and when 4436 is adopted by Apple, Microsoft, etc.  I think if they
can arp for the default router of a lease they once had, they will use
that lease until a dhcp server tells them not to (this could momentaraly
cause them to steal a lease if the server reallocates it early).

So I'd really only enter into using one-lease-per-client if you can't
avoid it.  For example because you need ddns teardowns on old leases
before granting new ones.

If you have no such restriction, try hard to find another way.

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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