Different IP every time

Hi,

is it possible to force the DHCP server to give a client
different IP
address every time the lease expire? Something like the PPP
LCP does.

-- 
Dario

 
> is it possible to force the DHCP server to give a
client different IP
> address every time the lease expire? Something like the
PPP LCP does.

    No. This is contrary to the protocol which requires the
server to 
give the same address if it possibly can. Nor will it
actually achieve
what-ever your managers are trying to accomplish; usually to
make it
more painful to run a server.
--
Bruce A. Hudson				| Bruce.HudsonDal.CA
UCIS, Networks and Systems		|
Dalhousie University			|
Halifax, Nova Scotia, Canada		| (902) 494-3405

Dario Protulipac wrote:

>is it possible to force the DHCP server to give a client
different IP
>address every time the lease expire? Something like the
PPP LCP does.

Firstly, as far as I know, the PPP LCP does not specifically
force a 
different address each time - you are probably just
observing what 
specific implementations do.

As far as DHCP goes, the RFC requires the server to try and
give each 
client the same address each time (not that Microsoft take
any 
notice, their server ignores that along with several other 
requirements).

What is your reason for wanting this ? I don't think we've
ever had a 
legitimate reason, usually it's "we are an ISP and my
manager insists 
we do this to stop <insert whatever>". Changing
the clients IP 
address is bad, really bad, and very dumb.

If that is the case, read on ...

It will not stop clients running server type applications
(that's why 
there are dynamic dns services). What it will do is break a
clients 
connections at regular intervals. Lets say you pick two
hours, and a 
client tries to download a big file that takes 2 1/2 hours
to 
download. After 2 hours (or less) the download will break,
and the 
user will probably try again, and again, and again. Many
clients 
(particularly http downloads) don't resume broken downloads
so each 
time the user is downloading <some large volume> of
data which is bad 
for the internet, bad for the server, and bad for you as the
ISP.

Eventually your customers will find out why their downloads
don't 
work and other connections get broken, and you will get
"bad vibes" 
that will make any worries about customers running servers
look 
trivial. Customers will leave as fast as they can and you
will go 
bust. Frankly, that is what stupid ISPs deserve !

Dario 



Simon Hobson wrote:
> Dario Protulipac wrote:
>
>   
>> is it possible to force the DHCP server to give a
client different IP
>> address every time the lease expire? Something like
the PPP LCP does.
>>     
>
> Firstly, as far as I know, the PPP LCP does not
specifically force a 
> different address each time - you are probably just
observing what 
> specific implementations do.
>
> As far as DHCP goes, the RFC requires the server to try
and give each 
> client the same address each time (not that Microsoft
take any 
> notice, their server ignores that along with several
other 
> requirements).
>
> What is your reason for wanting this ? I don't think
we've ever had a 
> legitimate reason, usually it's "we are an ISP and
my manager insists 
> we do this to stop <insert whatever>".
Changing the clients IP 
> address is bad, really bad, and very dumb.
>
> If that is the case, read on ...
>
> It will not stop clients running server type
applications (that's why 
> there are dynamic dns services). What it will do is
break a clients 
> connections at regular intervals. Lets say you pick two
hours, and a 
> client tries to download a big file that takes 2 1/2
hours to 
> download. After 2 hours (or less) the download will
break, and the 
> user will probably try again, and again, and again.
Many clients 
> (particularly http downloads) don't resume broken
downloads so each 
> time the user is downloading <some large volume>
of data which is bad 
> for the internet, bad for the server, and bad for you
as the ISP.
>
> Eventually your customers will find out why their
downloads don't 
> work and other connections get broken, and you will get
"bad vibes" 
> that will make any worries about customers running
servers look 
> trivial. Customers will leave as fast as they can and
you will go 
> bust. Frankly, that is what stupid ISPs deserve !
>
>
> .
>   
The idea is to give 24 hour lease and then change the
address. Managers 
want that because t-com do this in Croatia (using pppoe), so
the people 
are used to that. Any way, I'm aware that this is not how
DHCP should 
behave, but they insist on this because this is FTTH service
and they 
want some limitation so they can sell other FTTx services on
bigger 
price. Since this is political and not technical issue any
more, I'll 
thank You for Your answers and stop this thread hoping that
I won't be 
forced do patch the server 

Dario Protulipac wrote:

>The idea is to give 24 hour lease and then change the
address. Managers
>want that because t-com do this in Croatia (using
pppoe), so the people
>are used to that. Any way, I'm aware that this is not
how DHCP should
>behave, but they insist on this because this is FTTH
service and they
>want some limitation so they can sell other FTTx
services on bigger
>price. Since this is political and not technical issue
any more, I'll
>thank You for Your answers and stop this thread hoping
that I won't be
>forced do patch the server 


So it is "management want this broken behaviour"
!

I don't think you'll be able to modify the server to do
this, from 
what I gather the whole concept of addresses staying
constant is 
built deep into the logic and it would require some very
major 
changes to alter that.

Over here in the UK I see lots of stupid behaviour from ISPs
- like 
charging silly premiums for fixed addresses. With ADSL the
address 
pool is near enough required to be as big as your customer
base 
because so many are now permanently connected with hardware
routers 
and unlike dial-up you have to have a 'port' per user - it
certainly 
does cost a third of the basic service extra to offer a
fixed IP !

You could do some over subscription.  However, that won't
force a change 
at the end of the lease, unless the lease actually ends (ie:
The device 
is not turned on and updating the lease) it will just mean
that the 
device is likely to get a different IP when it comes back as
the 
previous IP will likely have been recycled.
Simon Hobson wrote:
> Dario Protulipac wrote:
>
>   
>> The idea is to give 24 hour lease and then change
the address. Managers
>> want that because t-com do this in Croatia (using
pppoe), so the people
>> are used to that. Any way, I'm aware that this is
not how DHCP should
>> behave, but they insist on this because this is
FTTH service and they
>> want some limitation so they can sell other FTTx
services on bigger
>> price. Since this is political and not technical
issue any more, I'll
>> thank You for Your answers and stop this thread
hoping that I won't be
>> forced do patch the server 
>>     
>
>
> So it is "management want this broken
behaviour" !
>
> I don't think you'll be able to modify the server to do
this, from 
> what I gather the whole concept of addresses staying
constant is 
> built deep into the logic and it would require some
very major 
> changes to alter that.
>
> Over here in the UK I see lots of stupid behaviour from
ISPs - like 
> charging silly premiums for fixed addresses. With ADSL
the address 
> pool is near enough required to be as big as your
customer base 
> because so many are now permanently connected with
hardware routers 
> and unlike dial-up you have to have a 'port' per user -
it certainly 
> does cost a third of the basic service extra to offer a
fixed IP !
>
>