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 From:  Jim Gifford <jim at giffords dot net>
 To:  "m0n0wall at lists dot m0n0 dot ch" <m0n0wall at lists dot m0n0 dot ch>
 Subject:  Re: [m0n0wall] Proxy ARP
 Date:  Tue, 17 Feb 2004 15:38:44 -0500
On Tue, Feb 17, 2004 at 01:14:55PM -0700, Chad R. Larson wrote:
> At 05:29 PM 2/15/2004, Mitch \(WebCob\) wrote:
> >Don't think it will keep your lease for you.
> An RFC compliant DHCP server is supposed to give you back the same IP 
> address as you last had, even if the lease has expired, as long as it has 
> not been reallocated.

You are right that the RFC states that the server SHOULD behave as you
said.  However, it says more on the behavior.  This is taken from RFC2131:

   As described in section 4.2, a server MAY, for administrative
   reasons, assign an address other than the one requested, or may
   refuse to allocate an address to a particular client even though free
   addresses are available.

In reality, many cable modem providers love to force address changes
periodically by forcing the server to require a new address for the

There was a period of time when the local cable company was forcing an IP
address change for each request and lease renewal request.  After a large
number of people complained about their TCP sessions crashing when IP
addresses changed, they stopped being quite so antagonistic.

Personally, I think too many ISPs are geared to feed consumers (as if
they were TV watchers) instead of customers, and are actually
anti-customer.  But that's another thread... ;)

Anyway, hope this helps.