the dhcp server will check assigned IP's over the network based on the
global period assigned on the server
( e.g. 3 days). If the IP ( client ) is still there, it will renew the
lease ( for another 3 days, etc.). If the client
IP is not connected, it will mark that IP address as available, and will
assign it to another machine as needed.
It can also ping an IP address BEFORE assigning it. So if you have static
IP addresses on the net being used
by a client, the dhcp server will mark that IP address as unusable, and
will not assign it to any other machine,
to avoid a conflict.
THe perid the server is set to renew a lease really should depend on the
type of clients. In a mobile environment
where machines are moved around a lot ( e.g. laptops ) from subnet to
subnet, you want to set the lease period
to be short, so that IP addresses will be available more often. When
machines are not moved often ( e.g. corporate net),
the lease period should be longer ( this also reduces network traffic and
server load ). THe default for NT server is
3 days.
Philippe Moutarlier <[EMAIL PROTECTED]> on 01/06/2000 09:24:17 PM
Please respond to [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
cc:
Subject: Re: DHCP IP Assignments, Linux vs Win98
I am doing a pretty weird thing to keep my IP but it looks like it is
working OK :
- I start the network using dhcp . give a look at the IP using ifconfig.
- I change the network config to NOT USE dhcp and assign manually the IP
obtained above.
I could keep my IP over 2 months this way till the server went down and
would not let me
use it anymore. However, I don't know how the sverer can know if you are
connected or not so
I don't know how long you can stay disconnected and get your IP running ok
when reconnecting.
If someone has info about how the server handles this, I would be glad to
know.
Philippe
"Hossein S. Zadeh" <[EMAIL PROTECTED]> writes:
> On Thu, 6 Jan 2000, M. Smith wrote:
>
> > Over the past two months or so, I've been experimenting with Linux RH
> > 6.0 as a gateway/firewall machine. I permanently switched to the Linux
> > firewall about a week ago. One thing I've noticed during
> > experimentation and since the switch is that the Linux machine gets a
> > different IP address everytime it boots.
>
> I have noticed this too. Here's the explanation I can provide:
>
> OK, first the easy one. Linux asks for a "lease" everytime eth0 (or
> whatever) is brought up. DHCP server assigns the next available IP
address
> (which is very likely different from the last one your machine's got).
>
>
> Windows machines however, "remember" their last IP address. Upon startup
> they send a "renewal" request to the DHCP server (rather than initiating
a
> new lease).
>
> If the IP is available, it is re-assigned to the machine with a DHCP
"ACK"
> packet.
>
> If the IP is not available, a "NACK" is sent. Then the windows machine
> asks for a new lease, and the server provides an IP.
>
> Using the above method has a couple of distinct advantages:
> 1) the machine gets the same IP address every time (provided the IP is
not
> assigned to somebody else).
> 2) if the server is not available, the Windows machine keeps the IP
> (until expiry of course).
>
> The second point above is very improtant for mobile users, because if you
> are on the road, services (like web servers) do not hang waiting for
their
> IP address. I know this because if my laptop is not connected, I don't
> even bother booting Linux. RedHat 6.1 startup scripts seems to address
> this startup problem.
> In addition, if someone reboots his workstation while a DHCP server is
> temporarily unavailable, he won't get stuck.
>
>
> cheers,
> Hossein
>
>
>
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