WLC Fast SSID Switching

[waller.brad]

I have having an issue that I have found Fas SSID switching would resolve.What I want to know is if their are any negative sideeffects to this being enabled. A WLC reboot, WAP reboots, or any other issues that can arise.

My networking and Cisco knowledge is limited, I was thrown into something and am doing my best with the knowledge I have, so I appreciate the

patience.

[George Stefanick]

Hi Brad,

Welcome to CSC ..

If you enable FAST SSID no reboot is needed. It takes effect once you hit apply.

http://www.my80211.com/cisco-wlc-cli-commands/2010/5/9/wlc-configuring-fast-ssid-changing.html

[waller.brad]

Thank you very much. Are there any reported end user side effects? I wouldn't think there would be, I just need to be sure.

[George Stefanick]

Not that I am aware of. Ive deployed this for many customers. I also have it enabled on a large network I manage now. We have over 6k+ wifi devices, 40+ WLCs. No reported issues.

What you will notice, clients will move from one ssid to another quickly. It is noticable from that point, yes.

Say they're connected to the GUEST WLAN and then move to a PRODUCTION WLAN. You will not see a delay in connection.

[Justin Kurynny]

George,

Fast SSID changing is an interesting setting and I've always found it a little mysterious. If it is not enabled, the WLC will enforce a delay before allowing clients to move from one SSID to the next. I noticed you did a post on this a while back, so I was wondering if you happened to know why fast SSID changing is even an option, why it's disabled by default, and if you know what the coded required delay between changes is.

Justin

[George Stefanick]

Hey Justin,

I suspect, and this is only my idea, the reason why it may be disabled is to prevent supplicants from jumping WLANs / SSIDs. Ive worked with some clients that if they got a deauth frame, say from session timeout, it could prevent it from jumping to another SSID that it was configured for. But again, this is only my 2 pennys. Obvious there is a reason if Cisco put it in the sauce.

As for the timer itself. I had that documented somewhere. I opened a case with TAC about this, god over a year ago. Let me see if I can find it ..

Perhaps Wesley can shed some light on this for us !

[Justin Kurynny]

George,

I think that's a pretty good theory. I thought that maybe there was something to do with anti-DOS, wherein if a client could continually jump back and forth between SSIDs, the WLC could slow down processing the database session rewrites, so by default it says, no, you can't do that.

There's probably some simple explanation that I'm missing, so yeah, maybe someone out there knows a little bit and can share some info.

Thanks!

Justin