Inter-Subnet Roaming

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Jul 27th, 2007
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We have multiple 4404 controllers in the same mobility group. Because our controllers are placed into different buildings and our common SSID is set on WLANs on different VLANs/subnets, I would like to ensure "inter-subnet roaming" occurs in case a client inadvertently roams between access points on controllers in different WLANs (subnets).

Do I have to manually set every controller to be a mobility anchor for the same WLAN? Does a mobility anchor have to be set before "inter-subnet" roaming will occur? (In this case, every controller would be an anchor.)

I have read the section of the 4.0 guide on inter-subnet roaming, mobility anchors, etc. but it is still unclear.

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ankbhasi Fri, 07/27/2007 - 07:05
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Hi Friend,

The concept of mobility anchor is that you can manually define which controller will going to be a anchor controller for your client no matter client connectes to whicever controller first but if your requirement if just internet subnet roaming then you do not need mobility anchor and to whichever controller client associate first via an AP that controller will going to be an anchor controller and when client roams to other controller then that controller will going to be a foreign controller.

So in short in internet subnet setup whicever controller client associate first becomes an anchor controller and in mobility anchor setup you can manually define which controller should be an anchor controller.



*Pls rate all helpfull post

sometechguy Fri, 07/27/2007 - 07:21
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Thank you for the reply.

If that is the case, then inter-subnet roaming is not working correctly in our environment. I have roamed between two access points that are associated with different controllers. These controllers are in separate buildings with the common SSID on different subnets. When I roam between the access points, I do not keep the same IP address. The IP address changes when the client associates between access points. Isn't the IP addresses supposed to remain on the client during inter-subnet roaming?

ankbhasi Fri, 07/27/2007 - 08:58
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  • Cisco Employee,

Hi Friend,

Yes the ip address of the client should be retained when client roams and that is the whole concept of mobility/roaming.

As per your description I believe mobility peers are not configured. Can you paste me the output of "sh mob summary"?



sometechguy Fri, 07/27/2007 - 10:19
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I created a new WLAN/SSID and set the mobility anchor as "local" on each controller for that WLAN. I was then able to roam between WLANs on different subnets and did not lose the IP address. So, I think it is resolved.

Just in case, I'll go ahead and post output from "sh mob summary":

Mobility Protocol Port........................... 16666

Mobility Security Mode........................... Disabled

Default Mobility Domain.......................... MOB

Mobility Group members configured................ 4

Switches configured in the Mobility Group

MAC Address IP Address Group Name






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