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multiple dhcp scopes for single vlan/subnetting

Hi all,

      We currently have a vlan64 with a /24 subnet mask.  Our ip range is x.x.64.0 -> x.x.79.254, and we have a microsoft dhcp server setup to provide IP addresses for our clients in x.x.64.10-> x.x.64.200.  We now have a need to provide a building with separate ip addresses in the same /24 subnet range, for instance x.x.66.x.  I can manually set the clients to that ip address (IE x.x.66.10) and they can route and communicate fine.  However, I don't know if there is a way to force clients in this building to use a specific dhcp scope.  Are there any configurable options on the switch?  

      As a thought, I tried creating a separate vlan 66, created an interface on the vtp master switch (cisco 3750), and attaching clients to that vlan, but they cannot route (static ip) or grab a dhcp address.  I cannot set an ip address on that interface either:  

            >ip address x.x.66.x 255.255.240.0
             x.x.64.0 overlaps with Vlan64

      I am hoping someone might have some insight on how to do this.  I'd rather not have to break up the vlan, we'd have quite a bit of reconfiguration to do on static devices.

(Edit: sorry, for whatever reason this question got added to the vpn zone.  I don't see a way to remove it from that zone....)
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wilsonb162
Asked:
wilsonb162
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2 Solutions
 
AmirchoupaniCommented:
Just define your scope and set a relay agent on your VLAN interface (the one connected to the building) to forward DHCP broadcasts to your DHCP server.
The DHCP server automatically will lease the IP addresses from the proper scope. Because whenever a relay agent contacts DHCP for an IP lease, DHCP checks the relay agent's IP and lease an IP from the scope that has same NetID as the relay agent's.
Good Luck
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wilsonb162Author Commented:
At the moment, our switch configurations look something like this:

--------- remote building ---------------
interface FastEthernet0/2
 switchport access vlan 64
etc.....

interface VLAN64
 ip address x.x.79.x 255.255.240.0
 no ip directed-broadcast
 no ip route-cache
--------------------------------------------

------------- core vtp master ------------
interface Vlan64
 ip address x.x.64.x 255.255.240.0
 ip helper-address x.x.x.x
---------------------------------------------


we also have two scopes:  x.x.64.x/24 and x.x.66.x/24
the dhcp server is still handing out just x.x.64.x addresses.  Do I need to reconfigure the interface on the remote switch to a x.x.66.x address and configure the dhcp-helper there?  will the dhcp-helper on the core vtp switch override the helper on the remote switch?


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AmirchoupaniCommented:
You need to set the dhcp-helper just on the VLAN or switch interface that is connected to your other buildings clients.
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wilsonb162Author Commented:
Well, that would mean we would have to remove the dhcp-helper from our core and reconfigure all of our switches.  That might be doable.  

Any further thoughts from anyone?
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DonbooCommented:
Since you have a 3750 I think you should use the routing in it and make a vlan 66 for the remote building, give it a different IP address that is in a different subnet like 192.168.1.0 /24 and then trunk to the remote building.

--------- remote building ---------------
interface FastEthernet0/2
 switchport encapsulation dot1q
 switchport mode trunk
!
interface VLAN66
 ip address 192.168.1.2 255.255.255.0
 no ip directed-broadcast
 no ip route-cache
 ip helper-address x.x.x.x
!
ip default-gateway 192.168.1.1 (so you can access the switch from another network)
--------------------------------------------

------------- core vtp master ------------
vlan 66
 name "remote building name"
!
interface Vlan64
 ip address x.x.64.x 255.255.240.0
 ip helper-address x.x.x.x
!
interface Vlan66
 ip address 192.168.1.1 255.255.255.0
!
interface g0/"whatever number goes to the remote building"
 switchport encapsulation dot1q
 switchport mode trunk
---------------------------------------------

This is ofcourse without knowing your IP scheme at all so I cant tell you that it will fit into your network but looking at your IP addressing of vlan64 I´d recommend you start working on a plan to segment. (Again depending on how many clients you have on vlan 64)
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DonbooCommented:
Forgot to mention to configure the IP dhcp scope that corresponds to VLAN 66 on the DHCP server.
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wilsonb162Author Commented:
We might end up re-doing our subnetting then.  We don't have a need for such a large subnet if we can't assign multiple DHCP scopes to the same subnet.  This just means that there will be more routing for stuff like printers that will now be separated onto different subnets.
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wilsonb162Author Commented:
Sorry guys, I thought I closed this out.  Both solutions I am awarding points to are valid, although segmenting into a separate VLAN would be cleaner.
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wilsonb162Author Commented:
Hmm, I wanted Donboo to get an A... is there any way to split ratings as well as points?
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QlemoC++ DeveloperCommented:
I've requested attention on your behalf (see button in original post, bottom right corner). An admin will take care of this, or re-open the question and tell you how to do grade yourself.
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modus_operandiCommented:
Grade changed to 'A'
 
modus_operandi
EE Moderator
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