I think it's more commonly used to override the server's default:
man dhcpd:
...
It is possible to specify two lease lengths: the default
length that will be assigned if a client doesn't ask for
any particular lease length, and a maximum lease length.
You can request a lease time such that SERVER DEFAULT < requested lease <
max lease.
Poorly configured DHCP servers that use the default of one day aren't
optimal. Really when you setup the server you should define the default
lease time that makes sense (the manpage has an example, an office
environment where machines aren't added/removed frequently could be a
month or more, whereas a test environment where machines are just powered
on, tested, and shipped out could be 30mins). Then specify a max_time so
clients that are very static (the admin's workstation, for instance) can
request a much longer lease time.
Anyways, it must have some use otherwise Vix would've removed it. I'd
rather have the option than not have it.
Adam Maloney
Systems Administrator
Sihope Communications
On Tue, 3 Oct 2000, Thomas T. Veldhouse wrote:
> That is interesting. However, I have never seen a server configuration that
> didn't have a lease time specified in it - so in practice, it is probably
> meaningless to request a given lease time.
>
> Tom Veldhouse
> veldy at veldy.net
>
> ----- Original Message -----
> From: "Adam Maloney" <adamm at sihope.com>
> To: <tclug-list at mn-linux.org>
> Sent: Tuesday, October 03, 2000 10:45 AM
> Subject: Re: [TCLUG:21970] Should DSL or Cable modem
>
>
> > man dhcpcd...
> >
> > -l leasetime
> > Specifies (in seconds) the recommended lease time
> > to the server. (Note that the server can override
> > this value if it sees fit). This value is used in
> > the DHCP_DISCOVER message. The default is infinite
> > (0xffffffff).
> >
> > By default the client will request infinity, and the server will send it's
> > configured default lease time back in the Offer. You can't force it from
> > the client side, the server always wins (just like Awk!)
> >
> > Adam Maloney
> > Systems Administrator
> > Sihope Communications
> >
> > On Tue, 3 Oct 2000, Thomas T. Veldhouse wrote:
> >
> > > He seemed to be talking about changing the lease time in the already
> > > negotiated lease file. I wasn't aware you could even configure DHCP
> clients
> > > to ask for a given release interval. I never saw such an option when
> > > setting up DHCP client.
> > >
> > > Tom Veldhouse
> > > veldy at veldy.net
> > >
> > > ----- Original Message -----
> > > From: "Adam Maloney" <adamm at sihope.com>
> > > To: <tclug-list at mn-linux.org>
> > > Sent: Tuesday, October 03, 2000 10:23 AM
> > > Subject: Re: [TCLUG:21970] Should DSL or Cable modem
> > >
> > >
> > > > No, if he tells the client to ask for a lease time of 3 weeks, the
> client
> > > > sends that during the negotiation. The server can reject that lease
> time
> > > > if it's too long with a NACK followed by another OFFER with a more
> > > > plausible lease time.
> > > >
> > > > Maybe I mis-understood what he said though. Did he just change the
> lease
> > > > time in the file that dhcpcd writes with the state information?
> That's
> > > > bad. Really bad. If he changes the lease time there then the server
> > > > doesn't know about it. Then you're right, if he sets that to 3 weeks
> and
> > > > the initial lease was for 2 weeks, then after 2 weeks the server will
> be
> > > > expecting a renew that it will never get. It'll assume the client's
> gone
> > > > and put the IP back into the pool. If a new subscriber came along
> they
> > > > could snag up "his" IP legitimately. Then after a week his client
> will
> > > > try to renew the IP and the server will NACK it because it's already
> been
> > > > leased. Not to mention all the problems he'd have with IP conflicts.
> > > >
> > > > Adam Maloney
> > > > Systems Administrator
> > > > Sihope Communications
> > > >
> > > > On Tue, 3 Oct 2000, Thomas T. Veldhouse wrote:
> > > >
> > > > > Right. But if he changes the lease time to 3 weeks, but the server
> is
> > > > > configured for 2 weeks, there may be a 1 week period where two
> different
> > > > > computers share the same IP address, because somebody else has
> received
> > > the
> > > > > IP address, and his computer will not ask to renew the old IP
> address
> > > for
> > > > > another week yet.
> > > > >
> > > > > Tom Veldhouse
> > > > > veldy at veldy.net
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "Adam Maloney" <adamm at sihope.com>
> > > > > To: <tclug-list at mn-linux.org>
> > > > > Sent: Tuesday, October 03, 2000 9:30 AM
> > > > > Subject: Re: [TCLUG:21970] Should DSL or Cable modem
> > > > >
> > > > >
> > > > > > Well if his dhcp client sends a Renew request to the server, the
> > > server
> > > > > > can reject it. The dhcp client will then just ask for a new IP.
> As
> > > long
> > > > > > as he doesn't muck with the client (or bypass it altogether and
> just
> > > > > > statically configure it) he can't cause any trouble. The server
> can
> > > > > > always reject renew requests if the address has already bgeen
> > > reassigned.
> > > > > > I don't think there's anything he can do to the configuration of
> the
> > > > > > client that could screw anything up, I think he'd have to modify
> the
> > > > > > source.
> > > > > >
> > > > > > If the IP has already been leased to someone else, and his client
> asks
> > > for
> > > > > > that IP (in a renew request) the server will send a NACK back,
> then an
> > > > > > OFFER with a new IP.
> > > > > >
> > > > > > In any case, by changing the lease time you're probably not
> helping
> > > > > > yourself at all. As soon as the lease ends your client will send
> a
> > > renew
> > > > > > request back to the server and you'll get your IP back anyways.
> The
> > > lease
> > > > > > time just dictates how long before you have to renew again, but if
> the
> > > > > > server reboots you may be SOL. I believe ISC's stores the lease
> > > > > > information in /var somewhere so if the server restarts it'll know
> who
> > > has
> > > > > > what leased...but I don't know about whatever DHCP server they're
> > > using.
> > > > > > If it's Microsoft's it'll probably explode or something...
> > > > > >
> > > > > > Adam Maloney
> > > > > > Systems Administrator
> > > > > > Sihope Communications
> > > > > >
> > > > > > On Tue, 3 Oct 2000, Thomas T. Veldhouse wrote:
> > > > > >
> > > > > > > Yeah, and that somebody is going to be pissed if they find out
> that
> > > > > somebdoy
> > > > > > > is using their IP and causing them to have problems with there
> cable
> > > > > modem.
> > > > > > > Most users are not going to know what the problem is and they
> are
> > > simply
> > > > > > > going to call MediaOne and complain. If MediaOne then finds
> this,
> > > one
> > > > > had
> > > > > > > better watch out, because suddenly the support costs are larger
> than
> > > the
> > > > > > > profits that they are making off of the trouble causing
> individual.
> > > > > > >
> > > > > > > Tom Veldhouse
> > > > > > > veldy at veldy.net
> > > > > > >
> > > > > > > ----- Original Message -----
> > > > > > > From: "Adam Maloney" <adamm at sihope.com>
> > > > > > > To: <tclug-list at mn-linux.org>
> > > > > > > Sent: Tuesday, October 03, 2000 9:17 AM
> > > > > > > Subject: Re: [TCLUG:21970] Should DSL or Cable modem
> > > > > > >
> > > > > > >
> > > > > > > > Well if they ran ISC's DHCPd they can set Max-Lease-Time,
> which is
> > > the
> > > > > > > > maximum amount of time a given address will be leased for.
> That's
> > > not
> > > > > to
> > > > > > > > say that when the lease expires you won't renew and get it
> again,
> > > but
> > > > > if
> > > > > > > > you don't renew right away someone else will probably get it.
> > > > > > > >
> > > > > > > > Adam Maloney
> > > > > > > > Systems Administrator
> > > > > > > > Sihope Communications
> > > > > > > >
> > > > > > > > On Mon, 2 Oct 2000, Eric F Crist wrote:
> > > > > > > >
> > > > > > > > > Trust me, it works. I've gotten calls from TW and MediaDumb
> > > (aka
> > > > > ATT)
> > > > > > > and
> > > > > > > > > they've not been able to stop it, short of pulling the
> provision
> > > for
> > > > > > > your MAC
> > > > > > > > > address.
> > > > > > > > >
> > > > > > > > > But, there are ways around that too. =P
> > > > > > > > >
> > > > > > > > > On Mon, 02 Oct 2000, you wrote:
> > > > > > > > > >
> > > > > > > > > > Thats *only* if the other end accepts such bad things.
> > > > > > > > > >
> > > > > > > > > > AFAIK, you can setup ISC to ignore it.
> > > > > > > > > >
> > > > > > > > > > * Eric F Crist <ecrist at ardent-hacker.net> [001002 21:37]:
> > > > > > > > > > > After a little more research (I had a brain-fart) the
> file,
> > > on a
> > > > > > > freebsd =
> > > > > > > > > > system
> > > > > > > > > > > is /var/db/dhclient.leases
> > > > > > > > > > >=20
> > > > > > > > > > > This file is realatively simple and straightfoward. For
> > > > > information
> > > > > > > on y=
> > > > > > > > > > our
> > > > > > > > > > > box, type man dhclient.leases
> > > > > > > > > > >=20
> > > > > > > > > > > If you have questions or comments, feel free to email
> me.
> > > > > > > > > > >=20
> > > > > > > > > > >=20
> > > > > > > > > > >=20
> > > > > > > > > > > Au Contrair on the static IP. If you're into the
> computer
> > > > > hacking
> > > > > > > side of
> > > > > > > > > > > things, you can simply change your lease on the IP to
> never
> > > > > expire.
> > > > > > > Ther=
> > > > > > > > > > e's a
> > > > > > > > > > > file located on your hard drive that actually sets your
> > > lease.
> > > > > This
> > > > > > > is
> > > > > > > > > > > overwritten at the time of renewal by the DHCP server.
> I
> > > have
> > > > > done
> > > > > > > this =
> > > > > > > > > > myself
> > > > > > > > > > > and know others who do it successfully. Maybe not a
> legit
> > > > > static
> > > > > > > IP, but=
> > > > > > > > > > until
> > > > > > > > > > > they find out, who cares?=20
> > > > > > > > > > >=20
> > > > > > > > > > > On Mon, 02 Oct 2000, you wrote:
> > > > > > > > > > > > Disadvantages to cable modem (from my point of view)
> > > > > > > > > > > > - no static IPs, may be coming soon though
> > > > > > > > > > > > - no services on your machine, or you get booted
> > > > > > > > > > > >=20
> > > > > > > > > > > > Advantages to cable modem
> > > > > > > > > > > > - much faster
> > > > > > > > > > > >=20
> > > > > > > > > > > > I got this information from the Time Warner sales rep
> and
> > > the
> > > > > tech
> > > > > > > rep =
> > > > > > > > > > that
> > > > > > > > > > > > showed up at my apartment complex trying to get
> > > subscribers.
> > > > > > > > > > > >=20
> > > > > > > > > > > > --=20
> > > > > > > > > > > > Jon Schewe | http://eggplant.mtu.net/~jpschewe
> > > > > > > > > > > > For I am convinced that neither death nor life,
> neither
> > > > > angels=20
> > > > > > > > > > > > nor demons, neither the present nor the future, nor
> any=20
> > > > > > > > > > > > powers, neither height nor depth, nor anything else in
> > > all=20
> > > > > > > > > > > > creation, will be able to separate us from the love of
> God
> > > > > that=20
> > > > > > > > > > > > is in Christ Jesus our Lord. - Romans 8:38-39
> > > > > > > > > > > >=20
> > > > > > > > > > > >=20
> > > > > > > > > > >
> > > > > > >
> > > > ---------------------------------------------------------------------
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> > > > > > > > > > > --=20
> > > > > > > > > > > Eric F Crist
> > > > > > > > > > > System Administrator
> > > > > > > > > > > Ardent-Hacker.net
> > > > > > > > > > >=20
> > > > > > > > > >
> > > > > > >
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> > > > > > > > > > >=20
> > > > > > > > > >
> > > > > > > > > > --=20
> > > > > > > > > > Scott Dier <dieman at ringworld.org> #nicnac at efnet=20
> > > > > > > > > > http://www.ringworld.org/
> finger:dieman at destiny.ringworld.org
> > > > > > > > > >
> > > > > > > > >
> > > > > > > > > ----------------------------------------
> > > > > > > > > Content-Type: application/pgp-signature; name="unnamed"
> > > > > > > > > Content-Transfer-Encoding: 7bit
> > > > > > > > > Content-Description:
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> > > > > > > > > --
> > > > > > > > > Eric F Crist
> > > > > > > > > System Administrator
> > > > > > > > > Ardent-Hacker.net
> > > > > > > > >
> > > > > > > >
> > > > >
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