1. DHCP service has a VERY low processor utilization. All it does is sits
idle until it has to reply to requests for IP addresses and then issues
leases. The shorter the lease time, the busier the service becomes. However,
it IS a very vital service, needs to be reliable, and is very difficult to
"back up", so high-reliability hardware is a nice thing to have with DHCP, and
often, high-reliability goes hand-in-hand with high performance. (Have you
ever had to replace a DHCP server in the production environment of a large
enterprise? Duplicate IP addresses can create a really big ugly mess with the
users) In an enterprise enviroment, infrastructure engineers (sometimes the
NetEng's in association with a sysadmin) administer the DHCP server(s). Many
corporations put DHCP on their Primary Domain Controller not for the
processing power, but for the reliability of that specific NT host.
2. A computer does NOT universally lose its lease when it is rebooted.
Rather, it makes a DHCP request. If it does not receive a reply to its
request, it does one of a number of things, depending on the TCP/IP stack
implementation:
a. makes another request (common of the Microsoft TCP/IP stack)
b. keeps it's last IP address if the lease was still valid (I've seen
laptop computers/PCMCIA cards do this)
c. gets an autoconfiguration address (I've seen Win98 do this)
d. takes no ip address (I've seen NT4.0 do this)
3. DHCP is carried by UDP protocol, so it does not use "ACKs and all that
jazz". The client issues a broadcast message and receives the reply packet
from the DHCP server containing IP address, default gateway address, DNS
server address(es) from the DHCP server.
4. In small office remote environments, I've implemented a router (actually,
router/terminal server) as the DHCP server, especially when the alternative is
to keep a computer powered on 24x7 in a foreign country. The only challenge
there is the lack of address management tools when the router is serving the
IP addresses (the tools may have improved since IOS 11.1, though...). Chances
are, the router will stay up (higher MTBF) longer than any computer, and is
less likely to be powered off or rebooted.
Priscilla Oppenheimer <[EMAIL PROTECTED]> wrote:
> 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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