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 From:  Hilton Travis <Hilton at QuarkAV dot com>
 To:  "m0n0wall at lists dot m0n0 dot ch" <m0n0wall at lists dot m0n0 dot ch>
 Subject:  Re: [m0n0wall] Proxy ARP
 Date:  Wed, 18 Feb 2004 08:33:07 +1000
Hi Jim,

On Wed, 2004-02-18 at 06:38, Jim Gifford wrote:
> 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
> clients.

Yes, and for administrative reasons, this is quite acceptable, according
to the RFC.  The administrative reason, of course, being that their
T&C/AUP (often) says that on home Cable services you cannot run
servers.  So they change your IP if you miss a DHCP release renewal
(which generally happens only if your computer has been turned off) to
ensure your servers are difficult to access from external.  Of course,
Dynamic DNS will address many of the issues that a changed IP will
create.  :)

> 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.

People should have changed provider.  That tends to ring louder than
bitching at them constantly.

> 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... ;)

Don't forget that the Technical department of many ISPs is populated
with people as clued up about networking as most fresh MCSE graduates
are, or as your average houseplant is.  Most of them don't know what to
do when the question you ask isn't on their cheat sheet, and when you
ask them how they are doing, they get really scared as they haven't been
taught how to answer that.

This goes not only for "help" desk staffers, but also their sysadmin and
other tech staff.  Scary, but (unfortunately) true in too many cases.



Hilton Travis                   Phone: +61-(0)7-3343-3889
Manager, Quark AudioVisual      Phone: +61-(0)419-792-394
         Quark Computers         http://www.QuarkAV.com/
(Brisbane, Australia)            http://www.QuarkAV.net/

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