Need some Feedback on DHCP 80/20

I am looking into setting up DHCP 80/20 for gaining some fault tolerance. I
am running W2k3 Standard edition and realize I cannot use the clustering
feature that is available on the Enterprise edition. Has anyone implemented
the 80/20 using a domain controller/member server scenario? I am wanting to
find out if this is worth my time. Thanks in advance.

It doesn't really mater which servers you install the DHCP scopes on, just
so long as they don't have any addresses in common (duh!) and are both
authorised in AD. There is some special recommendation about credentials
when running DHCP on a DC. There will be an event in the event log
complaining about it that will point you to the right article which I can't
seem to find right now.

Typically it doesn't give you much redundancy anyway. Say you had 100
available leases split between two servers 80 available on one and 20 on the
other and assume that when responding to DHCP requests the servers give out
addresses evenly. So after only 40 machines have leases the server with
only 20 addresses is already unable to hand out any more leases. Then
assume you lose the "80" server. Your "20" server is STILL unable to hand
out leases since it's scope is full.

To get true redundancy you need a scope on each server that is capable of
servicing your entire environment. Say you needed to support 200 DHCP
clients on a single network with 10 servers. With only 210 devices you
might be tempted to simply use a C class rand with a 24-bit mask. If you
did an 80/20 or 50/50 split you'd still run into the issue I spoke of above
in the event of an outage.

A better config would be to choose a subnet that supports 400 workstations
and 10 servers with 200 avaailable leases on each DHCP server so that each
can support all 200 clients in the event of an extended outage.

Hope this helps.

Cheers,
Jeremy.

"Griff" <(E-Mail Removed)> wrote in message
news:BD3C1F86-893E-41D1-94BB-(E-Mail Removed)...
>I am looking into setting up DHCP 80/20 for gaining some fault tolerance. I
> am running W2k3 Standard edition and realize I cannot use the clustering
> feature that is available on the Enterprise edition. Has anyone
> implemented
> the 80/20 using a domain controller/member server scenario? I am wanting
> to
> find out if this is worth my time. Thanks in advance.

Jeremy-
Thank you for the information. We appreciate it!

"Jeremy" wrote:

> It doesn't really mater which servers you install the DHCP scopes on, just
> so long as they don't have any addresses in common (duh!) and are both
> authorised in AD. There is some special recommendation about credentials
> when running DHCP on a DC. There will be an event in the event log
> complaining about it that will point you to the right article which I can't
> seem to find right now.
>
> Typically it doesn't give you much redundancy anyway. Say you had 100
> available leases split between two servers 80 available on one and 20 on the
> other and assume that when responding to DHCP requests the servers give out
> addresses evenly. So after only 40 machines have leases the server with
> only 20 addresses is already unable to hand out any more leases. Then
> assume you lose the "80" server. Your "20" server is STILL unable to hand
> out leases since it's scope is full.
>
> To get true redundancy you need a scope on each server that is capable of
> servicing your entire environment. Say you needed to support 200 DHCP
> clients on a single network with 10 servers. With only 210 devices you
> might be tempted to simply use a C class rand with a 24-bit mask. If you
> did an 80/20 or 50/50 split you'd still run into the issue I spoke of above
> in the event of an outage.
>
> A better config would be to choose a subnet that supports 400 workstations
> and 10 servers with 200 avaailable leases on each DHCP server so that each
> can support all 200 clients in the event of an extended outage.
>
> Hope this helps.
>
> Cheers,
> Jeremy.
>
> "Griff" <(E-Mail Removed)> wrote in message
> news:BD3C1F86-893E-41D1-94BB-(E-Mail Removed)...
> >I am looking into setting up DHCP 80/20 for gaining some fault tolerance. I
> > am running W2k3 Standard edition and realize I cannot use the clustering
> > feature that is available on the Enterprise edition. Has anyone
> > implemented
> > the 80/20 using a domain controller/member server scenario? I am wanting
> > to
> > find out if this is worth my time. Thanks in advance.
>

"Griff" <(E-Mail Removed)> wrote in message
news:20D6FAEB-E459-4E7F-AD05-(E-Mail Removed)...
> Jeremy-
> Thank you for the information. We appreciate it!

I run 50/50 for the reasons Griff stated. 50% still may not cover the whole
IP segment but it will go longer before running out of addresses. I believe the
default DHCP lease time is 8 days which means the lease is attempted to be renew
at 4 days,...and not all machines expire at the same time which also buys more
time. So 50/50 gives you more time to get the down DHCP back up,..it also gives
you the same amount of time no matter which DHCP went down,..instead of having
the "80" go down and only leaving you "20".

Another thing to think about is if your IP segment has maybe 100 machines the
50/50 will carry you indefinately until you get the other one back up because if
you ran a traditional 24bit-254 host segment you have a potential 127 address
per DHCP.

--
Phillip Windell
www.wandtv.com

The views expressed, are my own and not those of my employer, or Microsoft, or
anyone else associated with me, including my cats.
-----------------------------------------------------

"Phillip Windell" <(E-Mail Removed)> wrote in message
news:OIp$(E-Mail Removed)...
> "Griff" <(E-Mail Removed)> wrote in message
> news:20D6FAEB-E459-4E7F-AD05-(E-Mail Removed)...
>> Jeremy-
>> Thank you for the information. We appreciate it!
>
> I run 50/50 for the reasons Griff stated. 50% still may not cover the whole

Sorry, meant Jeremy. Got your names turned around.

--
Phillip Windell
www.wandtv.com

The views expressed, are my own and not those of my employer, or Microsoft, or
anyone else associated with me, including my cats.
-----------------------------------------------------