multiple DHCP scopes question

this has always been a little unclear to me. I have only worked in
environments small enough that one dhcp server and one scope was all that
was needed however while studying for things I certianly come accross DHCP
questions concerning multiple scopes. I have seen depictions of networks
with multiple subnets all serviced by the same DHCP server with a different
scope for each subnet.

I am unclear as to how the right scope info is picked up by the right
subnet/clients?

1) does there need to be a seperate NIC for each respective scope for each
subnet? In other words, does the DHCP server have to have a seperate
physical connections for each subnet it services? Thats what I WAS under the
impression took place but after seeing serveral network depictions in sample
test questions that do not make that clear I am not sure... plus

2) what about one DHCP server located on subnetA that services that subnet
plus subnetB and subnetC which are behind routers? Each remote subnet has a
DHCP Relay agent running (or the router may support it). So how does the
DHCP server on subnetA know how to hand out the right scope info for each of
these 3 subnets?

These may be the same question... In my confused state I'm not sure but
asking them both should make clear what I'm trying to find out.

any info on this would be greatly appreciated.
thanks.

There are two different ways to service multiple subnets with a single DHCP
server:

1) One of the ways that a DHCP server can service multiple subnets is to
physically connect an adapter to each subnet with an appropriate static
address. When a server configured with multiple scopes receives a DHCP
broadcast discover packet on one of these interfaces, it will automatically
offer an IP from the scope which matches the IP that the broadcast was
received on.

2) The other way to service multiple scopes is to have one adapter in the
DHCP server and use relay agents. These can be hardware routers or
multihomed Windows servers. When a remote relay agent receives a broadcast
discover packet, it adds the IP of the interface on which the packet was
received to the header and then forwards a directed packet to the DHCP
server. The server then compares its available scopes to the IP in the
header and offers an address from the matching scope.

Doug Sherman
MCSE, MCSA, MCP+I, MVP

"djc" <(E-Mail Removed)> wrote in message
news:#(E-Mail Removed)...
> this has always been a little unclear to me. I have only worked in
> environments small enough that one dhcp server and one scope was all that
> was needed however while studying for things I certianly come accross DHCP
> questions concerning multiple scopes. I have seen depictions of networks
> with multiple subnets all serviced by the same DHCP server with a
different
> scope for each subnet.
>
> I am unclear as to how the right scope info is picked up by the right
> subnet/clients?
>
> 1) does there need to be a seperate NIC for each respective scope for each
> subnet? In other words, does the DHCP server have to have a seperate
> physical connections for each subnet it services? Thats what I WAS under
the
> impression took place but after seeing serveral network depictions in
sample
> test questions that do not make that clear I am not sure... plus
>
> 2) what about one DHCP server located on subnetA that services that subnet
> plus subnetB and subnetC which are behind routers? Each remote subnet has
a
> DHCP Relay agent running (or the router may support it). So how does the
> DHCP server on subnetA know how to hand out the right scope info for each
of
> these 3 subnets?
>
> These may be the same question... In my confused state I'm not sure but
> asking them both should make clear what I'm trying to find out.
>
> any info on this would be greatly appreciated.
> thanks.
>
>

Thank you!

great, clear, explanation. Its appreciated.


"Doug Sherman [MVP]" <(E-Mail Removed)> wrote in message
news:u1$(E-Mail Removed)...
> There are two different ways to service multiple subnets with a single
DHCP
> server:
>
> 1) One of the ways that a DHCP server can service multiple subnets is to
> physically connect an adapter to each subnet with an appropriate static
> address. When a server configured with multiple scopes receives a DHCP
> broadcast discover packet on one of these interfaces, it will
automatically
> offer an IP from the scope which matches the IP that the broadcast was
> received on.
>
> 2) The other way to service multiple scopes is to have one adapter in the
> DHCP server and use relay agents. These can be hardware routers or
> multihomed Windows servers. When a remote relay agent receives a
broadcast
> discover packet, it adds the IP of the interface on which the packet was
> received to the header and then forwards a directed packet to the DHCP
> server. The server then compares its available scopes to the IP in the
> header and offers an address from the matching scope.
>
> Doug Sherman
> MCSE, MCSA, MCP+I, MVP
>
> "djc" <(E-Mail Removed)> wrote in message
> news:#(E-Mail Removed)...
> > this has always been a little unclear to me. I have only worked in
> > environments small enough that one dhcp server and one scope was all
that
> > was needed however while studying for things I certianly come accross
DHCP
> > questions concerning multiple scopes. I have seen depictions of networks
> > with multiple subnets all serviced by the same DHCP server with a
> different
> > scope for each subnet.
> >
> > I am unclear as to how the right scope info is picked up by the right
> > subnet/clients?
> >
> > 1) does there need to be a seperate NIC for each respective scope for
each
> > subnet? In other words, does the DHCP server have to have a seperate
> > physical connections for each subnet it services? Thats what I WAS under
> the
> > impression took place but after seeing serveral network depictions in
> sample
> > test questions that do not make that clear I am not sure... plus
> >
> > 2) what about one DHCP server located on subnetA that services that
subnet
> > plus subnetB and subnetC which are behind routers? Each remote subnet
has
> a
> > DHCP Relay agent running (or the router may support it). So how does the
> > DHCP server on subnetA know how to hand out the right scope info for
each
> of
> > these 3 subnets?
> >
> > These may be the same question... In my confused state I'm not sure but
> > asking them both should make clear what I'm trying to find out.
> >
> > any info on this would be greatly appreciated.
> > thanks.
> >
> >
>
>