Windows XP DHCP Client behavior at boot?

[ohaya]

Hi,

I've been trying to track down a problem with getting an IP conflict
whenever Windows is booted.

As I've been investigating this problem, I was told that, in order to
speed up the boot process, the XP DHCP client will utilize the IP
address that was used previously whenever XP is rebooted.

In other words, if an XP machine has IP address 192.168.0.110 when it is
shutdown, it will 'assume' that that same IP address is valid when it is
rebooted, and, instead of sending out a DHCP request, it will just
assign that IP address, at least until the DHCP lease expires.

I haven't been able to find any references detailing this behavior, but
the problem that I'm trying to track down seems to fit with this
behavior:

- I shutdown one machine (Machine A) which has a specific IP address
- I startup another machine (Machine B), which happens to grab the IP
address that Machine A use to have
- I startup Machine A, and I get an IP address conflict.

Can anyone confirm that this is the way that the DHCP client in XP
works?

Also, is there any way to force XP to either clear its IP address when
it is shutdown, or to force XP to immediately issue a DHCP request when
it is booted?

Thanks in advance,
Jim

 

[Hans-Georg Michna]

I've been trying to track down a problem with getting an IP conflict
whenever Windows is booted.

As I've been investigating this problem, I was told that, in order to
speed up the boot process, the XP DHCP client will utilize the IP
address that was used previously whenever XP is rebooted.

In other words, if an XP machine has IP address 192.168.0.110 when it is
shutdown, it will 'assume' that that same IP address is valid when it is
rebooted, and, instead of sending out a DHCP request, it will just
assign that IP address, at least until the DHCP lease expires.

I'm not deeply into this, perhaps somebody else can chime in
with more precise knowledge, but I would say that, as long as
the lease is valid, there is no reason why a PC shouldn't keep
using it.

- I shutdown one machine (Machine A) which has a specific IP address
- I startup another machine (Machine B), which happens to grab the IP
address that Machine A use to have
- I startup Machine A, and I get an IP address conflict.

Can anyone confirm that this is the way that the DHCP client in XP
works?

As long as that IP address validly leased to machine A, the DHCP
server will not lease the same IP address to machine B, unless
the DHCP server is defective.

Also, is there any way to force XP to either clear its IP address when
it is shutdown, or to force XP to immediately issue a DHCP request when
it is booted?

I don't know, but it shouldn't be necessary. The only time when
a problem can occur is when the DHCP server is shut down and
restarted while there are still valid leases around. To minimize
this problem, avoid shutting down the DHCP server and reduce the
lease times in any small network to something like half an hour.
I always set the lease time to 30 minutes in small networks for
this reason.

Good DHCP servers may actually try to reserve the IP address for
each computer indefinitely, as long as there are enough other IP
addresses available for other computers. Mine does.

Could you describe your DHCP server?

Hans-Georg