Multiple DHCP Servers

Hello Newsgroup,

This is the initial situation:
- I got a class C and a class B net using the the same cabling
- The class B net now only contains devices with a fixed ip. The class C net
has a DHCP server.
- There is a router (logically) between the two nets and the class C nets
clients have a static route added towards the class B net router.

Unfortunate limitations:
- The used networking hardware is rather cheap, so there is no possibility
for setting up v-lans et cetera.
- Right now, there is not enough manpower to phisically seperate the two
nets.

Question if the following is possible in the current situation:
- Is it possible to set up a second DHCP server for the class B net without
messing up the existing server and clients in the class C net.
- If yes, how do I determine which server a device uses to retrieve its ip.

Thanks in advance for your help
Chris

"Christian Schaeffler" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Question if the following is possible in the current situation:
> - Is it possible to set up a second DHCP server for the class B net
> without messing up the existing server and clients in the class C net.

No.
Buy a $40 dollar Switch or Hub and separate the Segments.

[Exisitng Switch]-----[Existing Router]----[Cheap Switch]
|
|
|
|
<segment-1> <segment-2>


Buy a better Switch when you can afford it.

What you have is a Multi-Net and you're wanting it to not act like a
Multi-Net. To make that happen you have to statically assign the Host of one
IP Segment (as you are doing) or get rid of the Multi-Net by separating the
segments.

Also, as additional information, the "Classes" don't really mean anything
any more. Masks and Subnets are defined by the number of bits in the mask.
255.255.255.0 is a "24 bit" mask. Even with what you might consider a Class
B, the subnets still shouldn't use a mask that is lower than 24 bits because
you should never have more than 250-300 host per segment. The 24bit mask
gives 254 Hosts which is the perfect size. Lower bit masks are used to
SuperNet segments where they pass over backbones between routers to keep the
routing tables smaller and more efficient, but then they get broken down
into smaller segments futher downstream.

With older routing equipment that forced the use of Classes, the IP
assignments had to be more carefully done so the segments that split up
futher downstream "fit" the over-all design. That is probably forgotten
skill since Classless Addressing makes things more simple.

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

[Exisitng Switch]---[Existing Router]--[Cheap Switch]
| |
| |
<segment-1> <segment-2>

Hello Phillip,

>
> No.
> Buy a $40 dollar Switch or Hub and separate the Segments.
>
> [Exisitng Switch]-----[Existing Router]----[Cheap Switch]
> | |
> | |
> <segment-1> <segment-2>
>
>
> Buy a better Switch when you can afford it.
--
> Phillip Windell
> www.wandtv.com
>
Thanks for you reply.
As I mentioned above, it is not that easy: Just buying a new (cheap) switch
is not the problem.
You would need a bunch of people to run through the buildings, check where
the cabels go to, mark the network outlets for the seperate nets, maybe even
install new cables in the walls - if there is only one network outlet in the
wall but you need to access both nets...
So I guess the answer is no without easy alternative.

Regards
Chris

"Christian Schaeffler" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> As I mentioned above, it is not that easy: Just buying a new (cheap)
> switch is not the problem.
> You would need a bunch of people to run through the buildings, check where
> the cabels go to, mark the network outlets for the seperate nets, maybe
> even install new cables in the walls - if there is only one network outlet
> in the wall but you need to access both nets...
> So I guess the answer is no without easy alternative.

Yes, you have much bigger problems to deal with,..such as redesigning and
rebuilding the entire physical topology of the facility.

How many machines/devices are on the entire LAN? In other words, how many
IP#s are in use *total*,...I don't care about subnets, just a raw total.


--
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)> schrieb im Newsbeitrag
news:(E-Mail Removed)...
> "Christian Schaeffler" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> How many machines/devices are on the entire LAN? In other words, how many
> IP#s are in use *total*,...I don't care about subnets, just a raw total.
>

220 used in the class C net and about 130 fixed in Class B.

"Christian Schaeffler" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
> "Phillip Windell" <(E-Mail Removed)> schrieb im Newsbeitrag
> news:(E-Mail Removed)...
>> "Christian Schaeffler" <(E-Mail Removed)> wrote in
>> message news:(E-Mail Removed)...
>> How many machines/devices are on the entire LAN? In other words, how
>> many IP#s are in use *total*,...I don't care about subnets, just a raw
>> total.
>>
>
> 220 used in the class C net and about 130 fixed in Class B.

Well if it was less than 250 hosts then I would day get rid of the second
subnet,...but with 340 host I won't recommend that. I think you are stuck
leaving it the way you are running it.

I guess I cannot accept the idea that a company that can afford a LAN of 340
Hosts is not willing to spend the money for a Layer3 switch and run a few
cables. That would not be acceptable to me if I worked there, in fact it
probably means they wouldn't be willing to spend money on other things they
should spend it on (like my wages and insurance),..so I would probably start
looking for somewhere else to work. That's up to you of course, but if they
won't spend the money for you to do your job properly, what good are they?

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

As you no doubt realise, your current setup is very innefficient. Traffic
from a machine in one subnet going to a machine in the other has to use the
network twice. I has to go to the router then back to the target machine
over the same wire.

Even if you could run a second DHCP server, it would not change that.
The reason you cannot run a second DHCP server is that DHCP works by using
LAN broadcasts. If both DHCP servers are on the same wire, machines would
get their config from whichever DHCP server replied fastest!

As Philip pointed out, the only way to improve the situation is to
segment the network to reduce the amount of traffic on the wire, or upgrade
the switches so that you can use vlans rather than the two logical networks
on one wire which you have.

"Christian Schaeffler" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Hello Newsgroup,
>
> This is the initial situation:
> - I got a class C and a class B net using the the same cabling
> - The class B net now only contains devices with a fixed ip. The class C
> net has a DHCP server.
> - There is a router (logically) between the two nets and the class C nets
> clients have a static route added towards the class B net router.
>
> Unfortunate limitations:
> - The used networking hardware is rather cheap, so there is no possibility
> for setting up v-lans et cetera.
> - Right now, there is not enough manpower to phisically seperate the two
> nets.
>
> Question if the following is possible in the current situation:
> - Is it possible to set up a second DHCP server for the class B net
> without messing up the existing server and clients in the class C net.
> - If yes, how do I determine which server a device uses to retrieve its
> ip.
>
> Thanks in advance for your help
> Chris
>
>
>

<snippage>
> Question if the following is possible in the current situation:
> - Is it possible to set up a second DHCP server for the class
> B net without messing up the existing server and clients in the
> class C net. - If yes, how do I determine which server a device
> uses to retrieve its ip.

As Phil said; you can't, the problem is that at the moment you
are not able to control which traffic flows where, this means that
DHCP packets will travel on both networks; a possible solution
to this would be buying a managed switch capable of performing
traffic filtering (or even handling VLANs) so that you'll be able to
block DHCP traffic flowing from one net to the other while, at the
same time, allowing regular traffic to flow