DHCP serves wrong IP address from an old VLAN

networking box

Here’s one of the issues which caused me a lot of headaches until we finally resolved it.

We have 4 vlans, one DHCP that has configured one superscope and a scope for each vlan (different subnet). When someone connects the laptop to VLAN3 for instance, the user gets the proper IP, but if he switches vlan to vlan1, he will get an address from vlan3.

If I release the IP address and renew it, I will again get the wrong VLAN3 address when physically connected to vlan1.

If I just type ipconfig /renew, I get an error message: Unable to contact the DHCP server.

We we’re investigating a lot but haven’t find the solution. It usually helped if if I made a DHCP reservation on vlan3 and remove the lease from vlan1.

Also, if I have changed the network adapter to static IP address and then trie to get a DHCP address, I usually got a proper IP address, in this case from vlan1.

Just to mention, that everything was working fine when we had DHCP server on each VLAN, but once we’ve consolidated our servers and started using only one DHCP server, this issues started to emerge.

Solution:
Remove the Scopes from the Superscope.

Solution I got was to remove the superscope and to recreate the scopes, but that wasn’t necessary. You only need to remove the scopes from the superscope. When the last scope is removed from the superscope, the superscope will automatically be deleted.

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2 Responses

  1. Andy says:

    True… have you had problems with superscopes coming back? When our service or server is re-started the superscopes come back causing the same problem.

  2. Nik says:

    You will need to remove every single scope from the superscope to delete the superscope. Then it won’t come back after service is restarted.

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