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DHCP adres in superscope

 
 
Peter
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      11-10-2005
Hello,

I have a 70-291 exam comming monday and have a simple question.
(I am from Holland so sorry for the grammar)

In the documentation they say that the DCHP server should be given an
address in the same local subnet as the DHCP's address scope. I can follow
that if the
address scope is set to 192.168.0.10/24 to 192.168.0.254/24 then the DHCP
server needs an address in the subnet 192.168.0.0/24.

So far so good???

But wat if you host a superscope with multiple subnets, like:
192.168.0.10/24 to 192.168.0.254/24 and 192.168.1.10/24 to 192.168.1.254/24
Then the address of the DHCP server cannot be in both subnets and I can't
fix is by giving the server an address like 192.168.0.1/23 because I don't
own that scope.

Can anyone (who can still follow me) help me with this brainstorm??

With kind regard,
Peter


 
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Kurt
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      11-10-2005

Correct me if I'm wrong, but I believe a superscope and multiple subnets are
two different things. If you want to give out DHCP addresses in a superscope
(via a normal broadcast DHCP exchange), you'd have to assume that hosts in
the broadcast domain can use any address in the scope. So the DHCP server
should have a subnet mask that encompasses the entire DHCP scope. If you're
handing out multiple scopes (subnets), you'd need a DHCP relay in a
contained broadcast domain to insure that you get an address from the
correct scope. Otherwise, it would just be a random chance that you get the
address for your subnet.

....kurt

"Peter" <(E-Mail Removed)> wrote in message
news:685cb$43739a2c$3ec2d90a$(E-Mail Removed).. .
> Hello,
>
> I have a 70-291 exam comming monday and have a simple question.
> (I am from Holland so sorry for the grammar)
>
> In the documentation they say that the DCHP server should be given an
> address in the same local subnet as the DHCP's address scope. I can follow
> that if the
> address scope is set to 192.168.0.10/24 to 192.168.0.254/24 then the DHCP
> server needs an address in the subnet 192.168.0.0/24.
>
> So far so good???
>
> But wat if you host a superscope with multiple subnets, like:
> 192.168.0.10/24 to 192.168.0.254/24 and 192.168.1.10/24 to
> 192.168.1.254/24
> Then the address of the DHCP server cannot be in both subnets and I can't
> fix is by giving the server an address like 192.168.0.1/23 because I don't
> own that scope.
>
> Can anyone (who can still follow me) help me with this brainstorm??
>
> With kind regard,
> Peter
>
>



 
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Peter
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      11-11-2005
Thanks for your awnser.
Isn't it superscopes are to support multiple subnets?
What static address does the DHCP server need?

This is wat Microsoft tells me.....

Using Superscopes
A superscope is an administrative grouping of scopes that is used to support
multinets,or multiple logical subnets on a single network segment.

Before passing a DHCP message on to a DHCP server, both RFC 1542 Compliant
routers and DHCP relay agents write their own address inside a certain field
(named Giaddr) within that message. This address recorded within the DHCP
message informs the DHCP server of the subnet ID of the originating subnet
of the DHCP request and, consequently, of the proper scope from which to
issue addresses to that subnet.

Greetzzz Peter

"Kurt" <(E-Mail Removed)> schreef in bericht
news:(E-Mail Removed)...
>
> Correct me if I'm wrong, but I believe a superscope and multiple subnets
> are two different things. If you want to give out DHCP addresses in a
> superscope (via a normal broadcast DHCP exchange), you'd have to assume
> that hosts in the broadcast domain can use any address in the scope. So
> the DHCP server should have a subnet mask that encompasses the entire DHCP
> scope. If you're handing out multiple scopes (subnets), you'd need a DHCP
> relay in a contained broadcast domain to insure that you get an address
> from the correct scope. Otherwise, it would just be a random chance that
> you get the address for your subnet.
>
> ...kurt
>
> "Peter" <(E-Mail Removed)> wrote in message
> news:685cb$43739a2c$3ec2d90a$(E-Mail Removed).. .
>> Hello,
>>
>> I have a 70-291 exam comming monday and have a simple question.
>> (I am from Holland so sorry for the grammar)
>>
>> In the documentation they say that the DCHP server should be given an
>> address in the same local subnet as the DHCP's address scope. I can
>> follow that if the
>> address scope is set to 192.168.0.10/24 to 192.168.0.254/24 then the DHCP
>> server needs an address in the subnet 192.168.0.0/24.
>>
>> So far so good???
>>
>> But wat if you host a superscope with multiple subnets, like:
>> 192.168.0.10/24 to 192.168.0.254/24 and 192.168.1.10/24 to
>> 192.168.1.254/24
>> Then the address of the DHCP server cannot be in both subnets and I can't
>> fix is by giving the server an address like 192.168.0.1/23 because I
>> don't own that scope.
>>
>> Can anyone (who can still follow me) help me with this brainstorm??
>>
>> With kind regard,
>> Peter
>>
>>

>
>



 
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Kurt
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Posts: n/a
 
      11-11-2005
> Before passing a DHCP message on to a DHCP server, both RFC 1542 Compliant
> routers and DHCP relay agents write their own address inside a certain
> field (named Giaddr) within that message. This address recorded within the
> DHCP message informs the DHCP server of the subnet ID of the originating
> subnet of the DHCP request and, consequently, of the proper scope from
> which to issue addresses to that subnet.
>
> Greetzzz Peter


Exactly. From another routed subnet, a relay (a workstation, server or
router acting as a relay) will listen for DHCP broadcasts from hosts on the
local subnet (subnet here meaning broadcast domain). It will relay the
request to the DHCP server on another subnet (via the router as a unicast).
Because the DHCP server knows the IP address of the relay agent, it will
assign an IP address from the scope with the same subnet address as the
relay. This would be accomplished with multiple scopes.

If you have a single subnet (broadcast domain again) that spans multiple
classful networks (like 192.168.0.0/22), you would create a superscope. In
order for the host to talk to the DHCP server via unicast (after they are
assigned an IP address), both host and DHCP server must have the same subnet
mask. I don't know if it's required to get an IP address for the server to
be within the range of the scope - give it a try and see what happens - but
best practices (and I would think the correct answer to any exam question)
would be that the DHCP server should have a subnet mask within the subnet of
it's brodcast-issued DHCP scope.


 
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joebob
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      11-14-2005
Peter wrote:

> But wat if you host a superscope with multiple subnets, like:



You can only superscope subnets within one network. You can can superscope multiple
subnets in 192.168.0.x's network, and you can superscope multiple subnets in 192.168.1.x's
network, but you can't superscope across networks. If you had this defined as superscopes-

192.168.0.x
192.168.1.x
192.168.2.x
192.168.3.x
192.168.4.x
192.168.5.x

With this, you've just let your dhcp server support 'multinets' using superscopes. You
don't need your server to be in any of the *other* superscopes you're providing dchp
service for, it will only *be* in the superscope for the subnet that you're initially
providing service for (if you hadn't made ur dhcp server static on that subnet to begin
with and excluded that ip from the serviced ip range.)


jb

(comments/corrections, welcome.)
 
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