Home Forums Microsoft Networking and Management Services DHCP PUZZLED: Multiple DHCP

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    Hi Guys,

    Had a look around and cant find a specific answer so hoping someone can help:)

    We are in the process of a network change.

    At the moment we have an old network 192.168.0 24. We ran out of addresses about 6 months ago so added a second scope 192.168.124.

    We now wish to move to a new network, breaking it up into Vlans, and having one scope per vlan.

    e.g. vlan 101 will have the scope of 10.20.101/24.
    vlan 102 will have the scope of 10.20.102/24 and so on.

    The Vlans are setup on new cisco switches, and have the IP helper set to the IP address of our windows dhcp server which is on the old network with a 192.168 address.

    Both the 192.168.and 10.20 networks can see and talk to each other as we are using a sonicwall nsa (firewall) that sits between them and allows them to talk.

    The DHCP server, has multiple scopes setup within a superscope for the new VLANs i.e. 10.20.101/24, 10.20.102/24 as well as the old 192.168.0/24 & 192.168.1/24 scopes.

    If I plug into a switch that is on the 10.20 side and configured to say VLAN 101 then I succesfully get an IP address of (I’ve excluded – .4).

    The problem I have is that the old network, which the majority of my company still sits on, when a client looks for a lease (when plugged into an old switch) it somehow gets leases from the wrong scope i.e. 10.20.101/24. When it needs to get a lease from one of the 192.168 scopes.

    Please can someone give me a few pointers to check !? My understanding is the lease allocation is decided by the gateway IP that the request comes from?! I cannot for the life of me figure out why leases are going into the wrong scope!



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