DHCP conflict with existing scope

[richard]

I'm trying to create two scopes.

The first scope will have a pool of addresses: 10.2.0.1->10.2.0.254
The second scope will allocate from the pool: 10.2.1.1->10.2.1.254

All client machines need the subnet mask 255.255.0.0 and are
physically on the same segment.

The reason I want this arrangement is that I have two types of client
machine, say type1 and type2, and I want the machines of type1 to be
given a 10.2.0.* address and machines of type2 a 10.2.1.* address. My
plan was to create reservations in the second scope for the type2
machines.

Trouble is, I get the message:

'The address range and mask conflict with an existing scope' when I
try to create the second scope.

Is is possible to do this?

Richard

 

[Herb Martin]

I'm trying to create two scopes.

The first scope will have a pool of addresses: 10.2.0.1->10.2.0.254
The second scope will allocate from the pool: 10.2.1.1->10.2.1.254

All client machines need the subnet mask 255.255.0.0 and are
physically on the same segment.

Then each DCHP server SHOULD have both scopes
configured -- with the same addresses. Then each scope
should have some or all of the addresses EXCLUDED
so that only one DHCP will ever give out that address.

Then since two scopes exist (for each DHCP server) on
the same (sub)network, you must create a SuperScope,
and add each scope to that superscope.

When you see or hear "superscope", thing "Scope Group".

The reason I want this arrangement is that I have two types of client
machine, say type1 and type2, and I want the machines of type1 to be
given a 10.2.0.* address and machines of type2 a 10.2.1.* address.
My
plan was to create reservations in the second scope for the type2
machines.

The reservations will be necessary since their is no
other (DHCP) way to distinguish which DHCP server will
provide addresses to particular machines.

Trouble is, I get the message:

'The address range and mask conflict with an existing scope' when I
try to create the second scope.
Is is possible to do this?

You need the superscope (after you have created the
individual scopes, reservations, and exclusions on
each DHCP server.

 

[richard]

Hi Herb

Then each DCHP server SHOULD have both scopes
configured -- with the same addresses. Then each scope
should have some or all of the addresses EXCLUDED
so that only one DHCP will ever give out that address.

There is only one DHCP server involved. I am trying to set up both
scopes on this single server, and it won't let me.

Then since two scopes exist (for each DHCP server) on
the same (sub)network, you must create a SuperScope,
and add each scope to that superscope.

I tried creating them within a superscope. I'm still not allowed.
I want this:

myScope1
start: 10.2.0.1
end: 10.2.0.254
mask: 255.255.0.0

myScope2
start: 10.2.1.1
end: 10.2.1.254
mask: 255.255.0.0

The only way I can get the DHCP server to accept the two scopes is to
give them masks such that the parts of the address pool where the mask
bits=1 are different, such as:

myScope1
start: 10.2.0.1
end: 10.2.0.254
mask: 255.255.255.0

myScope2
start: 10.2.1.1
end: 10.2.1.254
mask: 255.255.255.0

which works, but this is not the mask value I want the DHCP clients to
be given.

regards
Richard

 

[Herb Martin]

Hi Herb

There is only one DHCP server involved. I am trying to set up both
scopes on this single server, and it won't let me.

Then the answer is virtually the same but simple.

Create both scopes and superscope them.

I tried creating them within a superscope. I'm still not allowed.
I want this:

myScope1
start: 10.2.0.1
end: 10.2.0.254
mask: 255.255.0.0

myScope2
start: 10.2.1.1
end: 10.2.1.254
mask: 255.255.0.0

The only way I can get the DHCP server to accept the two scopes is to
give them masks such that the parts of the address pool where the mask
bits=1 are different, such as:

That should not be the case.

What OS (Win2000) and service pack level are
you using?

myScope1
start: 10.2.0.1
end: 10.2.0.254
mask: 255.255.255.0

myScope2
start: 10.2.1.1
end: 10.2.1.254
mask: 255.255.255.0

which works, but this is not the mask value I want the DHCP clients to
be given.

No, you should be able to give them the range and
subnet mask you wish to give.

Of course, in these cases two scope are not really
necessary -- just make it one scope and give out the
correct reservations.

 

[Richard G. Harper]

Yeah, that's going to happen. With a netmask of 255.255.0.0 that's going to
make both ranges overlap. You can't do what you want to do. Period. So
forget that and decide exactly why you want the two groups of addresses -
there should be no need to do so.

 

[richard]

Yeah, that's going to happen. With a netmask of 255.255.0.0 that's going to
make both ranges overlap. You can't do what you want to do. Period. So
forget that and decide exactly why you want the two groups of addresses -
there should be no need to do so.

The reason why is that I would then be able to apply different options
at the scope level.

However, if its not possible I will have to use a single scope and
exclude any address ranges I don't want.

regards
Richard

 

[richard]

That should not be the case.

What OS (Win2000) and service pack level are
you using?

2000 server sp4

Do you have a system running with scopes defined like this, or are you
thinking that logically it should be possible?

regards
Richard

 

[Richard G. Harper]

That (single scope, exclude addresses) is your only option if you must have
the address ranges and netmasks you detail. There's no way to make it work
(despite what the other Richard suggests) because the 255.255.0.0 netmask
will cause any address in the range of x.x.0.1 to x.x.255.255 to be in the
same range. Thus DHCP won't let you assign scopes x.x.0.0 and x.x.1.0
because the "new" 1.0 range is already covered by the existing 0.0 range.

--

 

[Guest]

Using 10.2.0.0 with a subnet mask of 255.255.0.0 is the reason you are having
problems, because that subnet also encompasses the 10.2.1.0 address space as
well.

10.2.0.1 - 10.2.255.254 is the host range when you apply the 255.255.0.0
subnet mask to this RFC 1918 space and that is why you get the overlap
message.

 

[Herb Martin]

2000 server sp4

Do you have a system running with scopes defined like this, or are you
thinking that logically it should be possible?

I thought (still pretty sure) that I had done this in
the past -- for a different reason.

You can still do the two scopes, if you don't allow
the ranges to overlap based on the mask.

10.10.1.0-254 /24
10.10.2.0-254 /24

If you want to the sets of machines to communicate
directly you will need to arrange this on the router,
or provide each machine a static route.

BTW: All this can be made simpler by just adding
another hub and router interface.

 

[richard]

Thanks to all for the help on this thread.

Richard