On Tue, Dec 2, 2008 at 9:59 AM, Jeff Bunting <[EMAIL PROTECTED]> wrote:
> I was reading about a Microsoft DHCP option to release the IP address
> on shutdown.
Yup, we use this, just to make things a little easier for roaming
users. Keeps the lease database cleaner, too.
> What I am curious to know is if the client actually releases the address or
> just tells the server it is released?
There's no way in the protocol for a DHCP server to acknowledge a
DHCPRELEASE message. So the client has to assume the message worked
("spray-and-pray"), and considers the interface to have no lease and
no address (until/unless renewed).
If the client is sending DHCPRELEASE and then keeping the lease,
that would be a DHCP protocol violation.
It should be easy enough to test. Before booting the troublesome
laptop, plug it into a hub without any upstream link (so the laptop
sees a link, but can't reach a DHCP server). Boot the laptop, and see
if it still thinks it has a DHCP lease. For added bonus points, watch
with a network sniffer.
On Tue, Dec 2, 2008 at 10:44 AM, Jeff Bunting <[EMAIL PROTECTED]> wrote:
> User brings in laptop from different network and can't get an address on
> new network.
Are you sure the user is doing a full shut down? I've sometimes
seen Windows "not notice" a change in link state. In other words,
computer is left running (or standby/suspend), unplugged from one
network and plugged into another, and Windows never realizes the
Ethernet cable was unplugged. Not much you can do about that.
In the ISC DHCP server, there's an option that marks a DHCP scope as
"authoritative" or not. If it's authoritative, the DHCP server will
send DHCPNAK to a client trying to get an address from a different
network. If it is not authoritative, the DHCP server will just not
answer. I dunno if MSFT DHCP has a similar option. If it does, might
help.
-- Ben
~ Finally, powerful endpoint security that ISN'T a resource hog! ~
~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/> ~
