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Author Topic: DHCP and VLAN change.  (Read 2506 times)

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Offline dimitry-nov

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DHCP and VLAN change.
« on: May 30, 2013, 06:22:41 AM »
I have AVAYA-based LAN, with Nortel 8630 core and  DHCP-server, which working in Windows 2008 Server. We have many pools for every subnet in our LAN. When user has moved computer in other switch port, which have another vlan, dhcp-server give him old address (from old vlan), which not work in new vlan. To fix this problem I do:
1) ipconfig /release
2) Delete IP-adress from DHCP-server
3) Disable network card in client computer
4) Enable network card and DHCP-server give right adress.

Question:Is it possible to automatically update the correct IP address when changing vlan on a switch port?

Offline Michael McNamara

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Re: DHCP and VLAN change.
« Reply #1 on: May 30, 2013, 08:47:47 AM »
I would believe that there's something more going on here. When ever you move a Windows device (link goes down on NIC) the operating system will attempt to issue a DHCP Discover when the link comes back up to verify that the IP address hasn't changed.  What version of Windows? What service pack are you using? I would guess this is a client side problem.
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Offline Johan Witters

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Re: DHCP and VLAN change.
« Reply #2 on: May 30, 2013, 06:07:56 PM »
I've seen this before... You should check the port the DHCP server is on: the port should only have 1 vlan configured on the port, and the ports needs to be "untagall". DHCP relay should be configured on the switch to pass the DHCP request from the client to the vlan of the server.

In case the switch port has multiple vlans configured on the switch, the server should have multiple (virtual) network cards with ip addresses in these vlans.

I've seen it happen with ip phones booting up in the default vlan, receive vlan parameters and boot into the voice vlan. At that point the phone again received a vlan 1 address. I then discovered the server had only 1 nic in the default vlan, but on the switch the port was in both default and voice vlan..

Good luck
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Network Engineer

Offline WindyMiller

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Re: DHCP and VLAN change.
« Reply #3 on: June 03, 2013, 05:34:36 PM »
I've seen this happen if you have a superscope configured.