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Ruisu
Asked: 2011-12-20 09:24:17 +0800 CST

Stop DHCP client from receiving old IP address on new VLAN

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I have one DHCP server running Windows Server 2008 R2. It is configured with one Superscope which contains 5 member scopes. One scope for each one of my subnets.

Here is the problem, if I am on VLAN 12 I get a VLAN 12 IP but if I disconnect my laptop and walk over to a port that is on VLAN 1 and reconnect nothing works. Makes sense because my laptop still has the VLAN 12 IP address. I perform a ipconfig /release followed by a renew but I get the same IP address which is still a VLAN 12 address!

I am guessing this is because my laptop is requesting to have the same IP address. How can I have my laptop not request the same IP? Or better yet, how can I configure DHCP to know that the laptop is on another VLAN and not to give it the same IP?

vlan dhcp windows-server-2008-r2 dhcp-server

3 Answers

  1. Best Answer

    I'm not sure why you are using superscopes at all since you're using VLANS..

    You should try to use dhcp relay on the router that connects all these VLANS - I'm pretty sure it will work out for you.

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  2. Are you absolutely sure that it's your laptop keeping the IP, and not the DHCP server misguidedly assigning the same IP because it already has a lease for that MAC address (albeit on a different vlan)? Because you're still getting the same IP on a manual renew, I'd say the DHCP server is to blame here.

    The client system should be dropping its DHCP IP when it loses a link on the interface, but verify by checking the address between the disconnect and the reconnect on the other vlan. And feel free to be really sure by capturing the renewal conversation with wireshark.

    But, it sounds like the DHCP server's the issue - what DHCP server software is it running on, and how's it configured? And how is your relaying configured to get the requests over to the server from the different vlans?

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  3. This answer assumes you have already configured IP-Helper to relay DHCP requests and assigned the correct VLAN to the ports on the switch(es).

    Delete the DHCP Superscope on Windows 2008 R2, don't use Superscope. Don't worry, deleting Superscope will not delete the child scopes. Then, go to to properties of each scope, go to Advanced tab and select "Both" for Assign IP addresses dynamically to clients. Choose "Unlimited" for Lease duration to BOOTP clients. Then click Apply then Okay.

    Release and renew IP address on client workstations.

    They should now get the correct IP for their corresponding VLAN.

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