DHCP, one router, two subnets

Please help! I have one router presently serving a high school and a career
center. We are trying to separate these two schools into separate subnets on
the router. I need to be able to run a DHCP server on each side for each
LAN. My understanding is that if we set up another DHCP it will broadcast to
both sides, which we do not want. My co-worker sent me this configuration:

The router is set up to receive all traffic from NCUHS and NCCC via one of
its Eth ports and route it to where it is asking to go which is the internet
99% of the time or the ILN 1% it is then sent to the gateway router via a
second Eth port. There is a SonicWall sitting in drop-in mode between this
link. This core router can see all subnets and will talk on all subnets.

Can someone please tell me how to set this up? I'm a newbie at this routing
stuff . . .
Thanks,
WBGirl

If the router separates the two subnets, AND DHCP Relay/Forwarding is not
enabled on the router, then the DHCP server will only service broadcasts
from that network. A router separates networks into broadcast domains,
which essentially means that it normally does not forward broadcasts. this
behavior is overridden by setting up Relay's or Helpers.
--
--
Dusty Harper
Microsoft Corporation
----------------------------------------------------------------------------
This posting is provided "AS IS", with NO warranties and confers NO rights
----------------------------------------------------------------------------

"WBGirl" <(E-Mail Removed)> wrote in message
news:535B5128-2832-4CDC-90E8-(E-Mail Removed)...
> Please help! I have one router presently serving a high school and a
career
> center. We are trying to separate these two schools into separate subnets
on
> the router. I need to be able to run a DHCP server on each side for each
> LAN. My understanding is that if we set up another DHCP it will broadcast
to
> both sides, which we do not want. My co-worker sent me this
configuration:
>
> The router is set up to receive all traffic from NCUHS and NCCC via one of
> its Eth ports and route it to where it is asking to go which is the
internet
> 99% of the time or the ILN 1% it is then sent to the gateway router via a
> second Eth port. There is a SonicWall sitting in drop-in mode between
this
> link. This core router can see all subnets and will talk on all subnets.
>
> Can someone please tell me how to set this up? I'm a newbie at this
routing
> stuff . . .
> Thanks,
> WBGirl

Thanks Dusty. That helps; however my co-workers tell me that even though we
assigned a gateway address to the career center and a separate gateway
address to the high school, the router is broadcasting the DHCP from the high
school to everyone, essentially because the two subnets are not really
separate? What am I missing here? How do we make sure the router is really
separating the two different subnets?

"Dusty Harper {MS}" wrote:

> If the router separates the two subnets, AND DHCP Relay/Forwarding is not
> enabled on the router, then the DHCP server will only service broadcasts
> from that network. A router separates networks into broadcast domains,
> which essentially means that it normally does not forward broadcasts. this
> behavior is overridden by setting up Relay's or Helpers.
> --
> --
> Dusty Harper
> Microsoft Corporation
> ----------------------------------------------------------------------------
> This posting is provided "AS IS", with NO warranties and confers NO rights
> ----------------------------------------------------------------------------
>
> "WBGirl" <(E-Mail Removed)> wrote in message
> news:535B5128-2832-4CDC-90E8-(E-Mail Removed)...
> > Please help! I have one router presently serving a high school and a
> career
> > center. We are trying to separate these two schools into separate subnets
> on
> > the router. I need to be able to run a DHCP server on each side for each
> > LAN. My understanding is that if we set up another DHCP it will broadcast
> to
> > both sides, which we do not want. My co-worker sent me this
> configuration:
> >
> > The router is set up to receive all traffic from NCUHS and NCCC via one of
> > its Eth ports and route it to where it is asking to go which is the
> internet
> > 99% of the time or the ILN 1% it is then sent to the gateway router via a
> > second Eth port. There is a SonicWall sitting in drop-in mode between
> this
> > link. This core router can see all subnets and will talk on all subnets.
> >
> > Can someone please tell me how to set this up? I'm a newbie at this
> routing
> > stuff . . .
> > Thanks,
> > WBGirl
>
>
>

"WBGirl" <(E-Mail Removed)> wrote in message
news:F6561DA1-C977-42DA-9BCE-(E-Mail Removed)...
> Thanks Dusty. That helps; however my co-workers tell me that even though
we
> assigned a gateway address to the career center and a separate gateway
> address to the high school, the router is broadcasting the DHCP from the
high
> school to everyone,

How do you "know" that this is happening. Routers don't Typically broadcast
this anyway,..when you set a "DHCP Helper" up on the Router it usually
forwards to a specific DHCP Server. Also DHCP is *passive* it doesn't
broadcast anything anywhere,...it is the client machines that broadcast to
*find* and DHCP Server and this is always going to happen everywhere even if
ther is no DHCP Server as long as the clients are setup to get thier
addresses automatically.

> essentially because the two subnets are not really separate?

What does that mean?

> What am I missing here? How do we make sure the router is really
> separating the two different subnets?

How could it *not* be? If you run two different IP Subnets and they are
each plugged into their own port on the Router then they are separated


--

Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com

Hi Phillip,
Thanks for responding. My understanding is that both the career center and
the high school are connected to one port on the router, which is causing the
issue.

The router is set up to receive all traffic from NCUHS and NCCC via one of
> its Eth ports and route it to where it is asking to go which is the
internet
> 99% of the time or the ILN 1% it is then sent to the gateway router via a
> second Eth port. There is a SonicWall sitting in drop-in mode between
this
> link. This core router can see all subnets and will talk on all subnets.


Again, I'm a newbie and I'm questioning what my co-workers are telling me.
I'm thinking the same way you are, but their response is that because they're
both connected to the same port, there has to be some sort of "separation" on
the router, even though both domains are on separate subnets.
Many thanks for all your comments. I don't "know" that any of this is
happening, this is what I'm trying to understand . . .I've read up on the
DHCP stuff and understand what you're saying, but I feel I must be missing
something about the router.
Thanks,
Darla

"Phillip Windell" wrote:

> "WBGirl" <(E-Mail Removed)> wrote in message
> news:F6561DA1-C977-42DA-9BCE-(E-Mail Removed)...
> > Thanks Dusty. That helps; however my co-workers tell me that even though
> we
> > assigned a gateway address to the career center and a separate gateway
> > address to the high school, the router is broadcasting the DHCP from the
> high
> > school to everyone,
>
> How do you "know" that this is happening. Routers don't Typically broadcast
> this anyway,..when you set a "DHCP Helper" up on the Router it usually
> forwards to a specific DHCP Server. Also DHCP is *passive* it doesn't
> broadcast anything anywhere,...it is the client machines that broadcast to
> *find* and DHCP Server and this is always going to happen everywhere even if
> ther is no DHCP Server as long as the clients are setup to get thier
> addresses automatically.
>
> > essentially because the two subnets are not really separate?
>
> What does that mean?
>
> > What am I missing here? How do we make sure the router is really
> > separating the two different subnets?
>
> How could it *not* be? If you run two different IP Subnets and they are
> each plugged into their own port on the Router then they are separated
>
>
> --
>
> Phillip Windell [MCP, MVP, CCNA]
> www.wandtv.com
>
>
>

"WBGirl" <(E-Mail Removed)> wrote in message
news41C7294-6894-4174-9E13-(E-Mail Removed)...
> Thanks for responding. My understanding is that both the career center
and
> the high school are connected to one port on the router, which is causing
the
> issue.

It isn't that simple.

> Again, I'm a newbie and I'm questioning what my co-workers are telling me.
> I'm thinking the same way you are, but their response is that because
they're
> both connected to the same port, there has to be some sort of "separation"
on
> the router, even though both domains are on separate subnets.

It isn't that simple. The router may be setup with VLANs where separate
logical subnets share the same physical port.

> Many thanks for all your comments. I don't "know" that any of this is
> happening, this is what I'm trying to understand . . .I've read up on the
> DHCP stuff and understand what you're saying, but I feel I must be missing
> something about the router.

I suspect what you interpret to be happeing may not be happening at all, but
rather you are misinterpreting what you see. There is no real way for me,
sitting where I am, to know in that kind of detail, what you are seeing over
there when I am not there.

--

Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com