DHCP Reservations

I have added a 2nd gateway to our 192.168.1.0 LAN, and have to make a large
number of DHCP reservations to divert half of the traffic to it. We have 2
servers each running DHCP.

Can reservations be made from an excluded portion of the scope, in which
case both servers can assign the same reserved IP?
Or must they be made from the individual server's distribution pool, thus
consuming twice as many IPs?

TIA
--
Newell White

Hello,

You can enable address conflict detection:
http://technet2.microsoft.com/window....mspx?mfr=true
=>this will add extra time to get a dhcp lease

But DHCP is more meant to be a 80/20 split or two different scope. You may
use longer lease to survive an offline dhcp server.

This may help too:
http://technet2.microsoft.com/window....mspx?mfr=true


--
Cordialement,
Mathieu CHATEAU
English blog: http://lordoftheping.blogspot.com
French blog: http://www.lotp.fr


"Newell White" <(E-Mail Removed)> wrote in message
news:706D678F-8D69-4EA0-9785-(E-Mail Removed)...
>I have added a 2nd gateway to our 192.168.1.0 LAN, and have to make a large
> number of DHCP reservations to divert half of the traffic to it. We have 2
> servers each running DHCP.
>
> Can reservations be made from an excluded portion of the scope, in which
> case both servers can assign the same reserved IP?
> Or must they be made from the individual server's distribution pool, thus
> consuming twice as many IPs?
>
> TIA
> --
> Newell White

"Newell White" <(E-Mail Removed)> wrote in message
news:706D678F-8D69-4EA0-9785-(E-Mail Removed)...
>I have added a 2nd gateway to our 192.168.1.0 LAN, and have to make a large
> number of DHCP reservations to divert half of the traffic to it. We have 2
> servers each running DHCP.

The proper way to handle that is to use a Broadband device with two WAN
Ports. Run both lines into the same box (instead of a box on each line).
Then you still have only one gateway. The Broadband device will handle load
balancing or fail over with the two lines transparently from the rest of the
network even knowing about it.

--
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.
-----------------------------------------------------

That or a nice box running pfSense or one of the other multi-WAN
firewall servers/devices... That's how I have my office setup..

---
Jeffrey Randow
(E-Mail Removed)
Windows Networking MVP 2001-2006
http://www.networkblog.net

On Tue, 23 Oct 2007 16:56:16 -0500, "Phillip Windell"
<(E-Mail Removed)> wrote:

>"Newell White" <(E-Mail Removed)> wrote in message
>news:706D678F-8D69-4EA0-9785-(E-Mail Removed)...
>>I have added a 2nd gateway to our 192.168.1.0 LAN, and have to make a large
>> number of DHCP reservations to divert half of the traffic to it. We have 2
>> servers each running DHCP.
>
>The proper way to handle that is to use a Broadband device with two WAN
>Ports. Run both lines into the same box (instead of a box on each line).
>Then you still have only one gateway. The Broadband device will handle load
>balancing or fail over with the two lines transparently from the rest of the
>network even knowing about it.

Thanks for input, Phillip and Jeffrey - in theory I am sure you are correct.
But if you work on an industrial estate in UK there is no cable TV, and the
only Broadband supplier is British Telecom.
The DSL service where you tell them what router you want costs $20k/year for
up to 100Mbaud.
The ADSL service where they provide the cheap and cheerful router is
$1k/year for up to 8Mbaud.
That is why we have two ADSL lines and two routers!

I found this in Windows Server 2003 Technical Library - DHCP Best Practices

"If you have more than one DHCP server reachable by a reserved client, add
the reservation at each of your other DHCP servers.
This allows the other DHCP servers to honor the client IP address
reservation made for the reserved client. Although the client reservation is
only acted upon by the DHCP server where the reserved address is part of the
available address pool, you can create the same reservation on other DHCP
servers that exclude this address."

So I have put the reservations in SERVER1 pool, and with same (exclusion
zone) IPs in SERVER2. It will be interesting to see if any clients end up
with SERVER2 as their DHCP server, then my question will be answered.

--
Regards,
Newell White


"Jeffrey Randow" wrote:

> That or a nice box running pfSense or one of the other multi-WAN
> firewall servers/devices... That's how I have my office setup..
>
> ---
> Jeffrey Randow
> (E-Mail Removed)
> Windows Networking MVP 2001-2006
> http://www.networkblog.net
>
> On Tue, 23 Oct 2007 16:56:16 -0500, "Phillip Windell"
> <(E-Mail Removed)> wrote:
>
> >"Newell White" <(E-Mail Removed)> wrote in message
> >news:706D678F-8D69-4EA0-9785-(E-Mail Removed)...
> >>I have added a 2nd gateway to our 192.168.1.0 LAN, and have to make a large
> >> number of DHCP reservations to divert half of the traffic to it. We have 2
> >> servers each running DHCP.
> >
> >The proper way to handle that is to use a Broadband device with two WAN
> >Ports. Run both lines into the same box (instead of a box on each line).
> >Then you still have only one gateway. The Broadband device will handle load
> >balancing or fail over with the two lines transparently from the rest of the
> >network even knowing about it.
>

Thanks for info Mathieu.

I know the 80/20 rule is the MS Tech Library orthodoxy, but in a 192.168.1.x
LAN with two DHCP servers and 75 hosts 50/50 is a no-brainer.
In general I can't think of a set-up where 80/20 is better - can you?
--
Regards,
Newell White


"Mathieu CHATEAU" wrote:

> Hello,
>
> You can enable address conflict detection:
> http://technet2.microsoft.com/window....mspx?mfr=true
> =>this will add extra time to get a dhcp lease
>
> But DHCP is more meant to be a 80/20 split or two different scope. You may
> use longer lease to survive an offline dhcp server.
>
> This may help too:
> http://technet2.microsoft.com/window....mspx?mfr=true
>
>
> --
> Cordialement,
> Mathieu CHATEAU
> English blog: http://lordoftheping.blogspot.com
> French blog: http://www.lotp.fr
>
>
> "Newell White" <(E-Mail Removed)> wrote in message
> news:706D678F-8D69-4EA0-9785-(E-Mail Removed)...
> >I have added a 2nd gateway to our 192.168.1.0 LAN, and have to make a large
> > number of DHCP reservations to divert half of the traffic to it. We have 2
> > servers each running DHCP.
> >
> > Can reservations be made from an excluded portion of the scope, in which
> > case both servers can assign the same reserved IP?
> > Or must they be made from the individual server's distribution pool, thus
> > consuming twice as many IPs?
> >
> > TIA
> > --
> > Newell White
>
>

Newell White wrote:
> Thanks for input, Phillip and Jeffrey - in theory I am sure you are correct.
> But if you work on an industrial estate in UK there is no cable TV, and the
> only Broadband supplier is British Telecom.
> The DSL service where you tell them what router you want costs $20k/year for
> up to 100Mbaud.
> The ADSL service where they provide the cheap and cheerful router is
> $1k/year for up to 8Mbaud.
> That is why we have two ADSL lines and two routers!

Hi Newell,

Even with the two lines and two routers, you should be able to knock
together a box with three network cards in it - one each for the two
routers and the other for your network, and then load-balance the public
connections. It'd be quite an interesting project!

As you say though, the DHCP solution is the easiest. Load balancing
would be much more elegant though.

--
Chris.

Since you are using private subnet, how can you be short of IP ?
You can use a /16 netmask or even /23 (same as 2 /24 but they can all
communicate without routing)

--
Cordialement,
Mathieu CHATEAU
English blog: http://lordoftheping.blogspot.com
French blog: http://www.lotp.fr


"Newell White" <(E-Mail Removed)> wrote in message
news:A6675210-5982-4ADB-8780-(E-Mail Removed)...
> Thanks for info Mathieu.
>
> I know the 80/20 rule is the MS Tech Library orthodoxy, but in a
> 192.168.1.x
> LAN with two DHCP servers and 75 hosts 50/50 is a no-brainer.
> In general I can't think of a set-up where 80/20 is better - can you?
> --
> Regards,
> Newell White
>
>
> "Mathieu CHATEAU" wrote:
>
>> Hello,
>>
>> You can enable address conflict detection:
>> http://technet2.microsoft.com/window....mspx?mfr=true
>> =>this will add extra time to get a dhcp lease
>>
>> But DHCP is more meant to be a 80/20 split or two different scope. You
>> may
>> use longer lease to survive an offline dhcp server.
>>
>> This may help too:
>> http://technet2.microsoft.com/window....mspx?mfr=true
>>
>>
>> --
>> Cordialement,
>> Mathieu CHATEAU
>> English blog: http://lordoftheping.blogspot.com
>> French blog: http://www.lotp.fr
>>
>>
>> "Newell White" <(E-Mail Removed)> wrote in message
>> news:706D678F-8D69-4EA0-9785-(E-Mail Removed)...
>> >I have added a 2nd gateway to our 192.168.1.0 LAN, and have to make a
>> >large
>> > number of DHCP reservations to divert half of the traffic to it. We
>> > have 2
>> > servers each running DHCP.
>> >
>> > Can reservations be made from an excluded portion of the scope, in
>> > which
>> > case both servers can assign the same reserved IP?
>> > Or must they be made from the individual server's distribution pool,
>> > thus
>> > consuming twice as many IPs?
>> >
>> > TIA
>> > --
>> > Newell White
>>
>>

You are right Chris,
Load balancing would be more elegant - but not the point of this exercise.

We are an electronics manufacturing plant, and we let production staff
listen to web radio while they work. This was OK until we started to get so
many East Europeans who listen all day, slowing down our VPN clients (sales
engineers).
Our MD tasked me with fixing this or banning web radio.
So I am just looking for segregated access, not fair shares for all!

--
Regards,
Newell White


"Chris M" wrote:

> Newell White wrote:
> > Thanks for input, Phillip and Jeffrey - in theory I am sure you are correct.
> > But if you work on an industrial estate in UK there is no cable TV, and the
> > only Broadband supplier is British Telecom.
> > The DSL service where you tell them what router you want costs $20k/year for
> > up to 100Mbaud.
> > The ADSL service where they provide the cheap and cheerful router is
> > $1k/year for up to 8Mbaud.
> > That is why we have two ADSL lines and two routers!
>
> Hi Newell,
>
> Even with the two lines and two routers, you should be able to knock
> together a box with three network cards in it - one each for the two
> routers and the other for your network, and then load-balance the public
> connections. It'd be quite an interesting project!
>
> As you say though, the DHCP solution is the easiest. Load balancing
> would be much more elegant though.
>
> --
> Chris.
>

From observation I can now answer my original question.

A W2k3 DHCP server can assign a lease to a reserved IP address which is
excluded from its' assignment pool.

At first sight this seems to imply that you can, and maybe should, create
identical reservations on two DHCP servers managing the same scope.

But there is a side-effect, which may (?) cause problems later.
If you manually re-configure the TCP/IP properties of a client, disabling
DHCP but preserving the reserved IP address, the reservation stays marked
Active in SERVER1 say.
Now if you re-configure TCP/IP on the client, enabling DHCP, it will ask for
a renewal of its' reserved IP address. SERVER2 might satisfy this request
first, and now both DHCP servers think they are managing the lease, and show
the reservation as Active.
I guess this should not cause any problem as the reservation is tied to the
unique MAC address of the client.
However, I will look at both DHCP servers after I shut my workstation down -
default for reservations seems to be 'Terminate on shutdown'.
--
Newell White