In my experience a 95/98/nt computer does retain the information regarding a
lease if it's shut down. I'm sure someone will correct me if I'm not right
on target.
When it next boots and initializes the tcpip stack it will send a broadcast
(or maybe unicast since it knows the address of the dhcp server it got the
address from) indicating (assuming the lease is still valid) "I have a lease
for this address, is it still valid" If the computer has moved to a
different network, a laptop for example, the DHCP server will send a NACK to
the client indicating that lease is invalid. If it doesn't get a response
or if the response is "you're good to go", it will continue with the current
address and try to renew at the normal intervals, 50%, 75%, 87.5%, then no
more web surfing.
If you look at the event viewer logs for an NT4 dhcp server with multiple
scopes in an environment where clients move around you will see lots
messages indicating this behavior.
Dave H
Here's a slice from technet
DHCP-supplied configurations are "leased" from the server. Periodically, the
client will contact the server to renew the lease. The protocol and
implementation are very robust and configurable, and short-term server or
network outages do not generally affect lease renewal. For example, DHCP
clients start to try to renew their lease when 50 percent of the lease time
has expired. Repeated attempts are made to contact the DHCP server and renew
the lease, until 87.5 percent of the lease time has expired. At this point,
the client attempts to get a new lease from any available DHCP server.
When a DHCP client is rebooted, it attempts to verify that the lease it
holds is valid for the current subnet. If it is moved to another subnet and
rebooted, the following sequence takes place:
Source Destination Source IP Destination IP Pro Description
davemacp *BROADCAST 0.0.0.0 255.255.255.255 DHCP Request (xid=6E3A2E74)
router *BROADCAST 10.57.8.1 255.255.255.255 DHCP NACK (xid=6E3A2E74)
davemacp *BROADCAST 0.0.0.0 255.255.255.255 DHCP Discover (xid=51CA7FED)
router davemacp 10.57.8.1 10.57.13.152 DHCP Offer (xid=51CA7FED)
davemacp *BROADCAST 0.0.0.0 255.255.255.255 DHCP Request (xid=2081237D)
router davemacp 10.57.8.1 10.57.13.152 DHCP ACK (xid=2081237D)
In this example the portable computer "davemacp" is moved to a new subnet
and re-started. It broadcasts a DHCP request for renewal of its old
parameters, but the DHCP server responsible for the new subnet recognized
that these were invalid for the subnet and NAK'd them. The DHCP client
software automatically went through a normal discovery process to get
reconfigured with parameters that are valid for the new location.
-----Original Message-----
From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED]]
Sent: Friday, March 16, 2001 3:17 PM
To: Russ Kreigh; [EMAIL PROTECTED]
Subject: Re: IOS DHCP vs NT DHCP
Well, obviously I went a little overboard with my example of a Pentium 4
for a DHCP server! &;-) But I'm still a bit queasy about running DHCP on a
slow server. Selecting a DHCP server requires an analysis of how many
clients ask for services at once, obviously, and how much processing power
that uses. I don't have any numbers. This would make a good research
project and white paper: Scaling DHCP Services. Hmmmmm....
Also, I got to thinking about my other brain-damaged response regarding
leases. If a computer is rebooted, it effectively loses its lease, doesn't
it? The lease time isn't stored anywhere in non-volatile RAM, is it? So, a
rebooted station would contact the DHCP server for a new lease. So for
companies that turn off their computers at night, a large flurry of DHCP
requests first thing in the morning could result in a processing bottleneck
at a slow server.
I work in a school where we do turn off all our computers at night. Maybe
most companies don't, although in California, they probably should!
Priscilla
At 08:39 PM 3/15/01, Russ Kreigh wrote:
>Am I missing something here? I mean an average DHCP process with the ACKs
>and all that jazz is not that much, probably less than 5k I would imagine.
>And there would be very little processing required to finish the request. I
>think it would take a LOT of requests to even bog down a Pentium 100 a
>little. It would be interesting to see some numbers, anyone have any?
>
>-Russ
>
>
> >An NT server could be installed on a machine with 512 MB of memory, a
>1GHz
>P4 processor, a speedy and large hard drive, etc.
> > > Since DHCP is mission critical to most networks, I would want it
running
>on a high-performance system that isn't also doing routing.
> > > >
> > > > Priscilla
>
>_________________________________
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________________________
Priscilla Oppenheimer
http://www.priscilla.com
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