Wireless Roaming

Unanswered Question
Dec 4th, 2007

Hi,

I have Layer 3 design "routed port" between access and distribution switches. I have also two wireless controllers.

As this design, every access switch users are using unique subnet, and let us say that i have three LW access points, every access point installed at access switch.

I configured mobility group between the two WLCs, my question:

When a wireless client roam between the APs, does the user obtained IP address change when roam between APs? Since each AP is connected tp separate layer 3 switch. If yes, how can we keep the obtained IP address while the client is roaming between the APs? Does the Auto-Anchor feature solve this problem?


Thanks


Abd Alqader

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Richard Atkin Tue, 12/04/2007 - 01:22

The answer is "no", clients will keep their original IP address while roaming, regardless of which AP they roam to.


The point to note is that when roaming between controllers, you can get a situation where ingress traffic (to WLAN Client) enters one WLC, but egress traffic (from WLAN Client) exits the other WLC. This is perfectly normal behaviour, but if you've implemented any restrictions on requiring symetrical traffic flows, you'll come a cropper.


The way around this is to implement "Symetric Tunneling" on both of your controllers. When implemented, ingress and egress traffic will always be sourced to/from the WLC the Client first associated to, and your Symetric traffic flow checks will be fine.

a.hajhamad Tue, 12/04/2007 - 02:04

Thanks for this valuable info.

1- This means that even we are using Layer 3 design "routed design", the WLAN client will always use the same ip address while romaing?

2- Did you mean by symetric tunneling is configuring mobility groups?

3- What about the auto-anchor feature, is it a must for the IP address issue or not?


Thanks


Abd Alqader

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