Solved: Trouble with many SSID's and many AP's

sin · ‎02-17-2010

I have a setup at a costumer where they use a lot of AP's in a building with a very open florplan arcitecture. This meens that a single laptop client can see 10 or more concurrent AP's.

The are also using 6 broadcasting SSID's. This meens that a single client sees beacons from around 60 AP/SSID combinations.

This result en very severy connectiong trouble from the clients. It seems to kill the wlan driver in windows XP. When limiting the number of SSID's to 4 the problem disapears. The problem is worst for Atheros interfaces but also present on Intel5300.

Any one have seen simular issue.

We are using Cisco WiSM 1131 and 1142 AP's

braggb001 · ‎02-18-2010

Just my 2 cents:

Adding APs to support additional users is fine as long as you do a site survey to make sure that this will not cause interference. Remember that B/G only has 3 usable channels, thus the more users you have connected per channel and the more interference on that channel the longer they will have to wait to transmit.
Although disabling SSID broadcasting does not improve security.....it will save resources. By default, wireless clients (phones, laptops, etc.) will attempt to join networks that they see automatically....this can mean hogging valuable bandwith and memory. If you add this to a dense AP deproyment with co-channel interference....which you probably have....you will definately see some issues.

Summary:

Adding APs doesn't solve all problems....no matter what Cisco says. Use Airmagnet or some other site survey utility to get a look at your environment. Disable SSID broadacsting on as many SSIDs as possible to save resources....not for security.

For further help, please attach your show run-config. Thanks.

View solution in original post

braggb001 · ‎02-17-2010

A Few Questions:

Are your running RRM?
What is your Beaconing Period set to for the network (A,B/G,N) you are attempting to connect to?
What code are you running on the WISMs?

sin · ‎02-17-2010

we do run rrm.

We have not changed the default beacon period. Where to config that?

We are running 6.0.188

Leo Laohoo · ‎02-17-2010

Maybe the AP's are deployed too close together. You could try to disable the radios to some of them and see if this helps.

sin · ‎02-18-2010

Well. It's one of the solutions we have thought about. However the costumer is a public school, with a very high number of computer with a heavy bandwidth demand. Therefor the big number of AP's are needed to meet those demands.

We have seen that disabling some of the SSID's solves the problem so right now we are trying to find a solution to minimize the number af requered SSID's. One thing would be to use AAA override to make the radius server provide the correct vlan.

But before this just on "tried and error" I like to have a more precise understanding of the issue.

How many beacon's is it safe to present to a laptop client before running in to this problem.

Are there any config on the controller part that can help minimize the problem.

I'm trying hard to get some answers from TAC right now, but I keep getting more questions than answers.

I think that setting some of the SSID's to non broadcast might help, but i'm not sure.

I'm trying to find out if changing the basic data rate to a higher rate would minimize the problem. This would meen that the beacon would transmit at a higher data rate - resulting i smaller cell's. Right ?

braggb001 · ‎02-18-2010

Just my 2 cents:

Adding APs to support additional users is fine as long as you do a site survey to make sure that this will not cause interference. Remember that B/G only has 3 usable channels, thus the more users you have connected per channel and the more interference on that channel the longer they will have to wait to transmit.
Although disabling SSID broadcasting does not improve security.....it will save resources. By default, wireless clients (phones, laptops, etc.) will attempt to join networks that they see automatically....this can mean hogging valuable bandwith and memory. If you add this to a dense AP deproyment with co-channel interference....which you probably have....you will definately see some issues.

Summary:

Adding APs doesn't solve all problems....no matter what Cisco says. Use Airmagnet or some other site survey utility to get a look at your environment. Disable SSID broadacsting on as many SSIDs as possible to save resources....not for security.

For further help, please attach your show run-config. Thanks.

sin · ‎03-19-2010

Just an update. Still working on this error.

We have a fine sitesurvey and no problems with inteferense. A new observation is that if we configure the windows xp machines to you only 2.4GHz og 5GHz there are no problems. Only when the client are in auto mode the problem accours.

It't is very clear that this relates to the number af active ssid's. At the moment we have 4 ssid's and no trouble but if we enable the 5th the problem comes back.

Does anyone have recomentation or experiense with many SSID's ?

We still have a tac case running, but up until now this have resulted in many qeustions and no answers

Rasmus

Screendump from floorplans in WCS attached

weterry · ‎03-20-2010

Have you tried changing the lowest Mandatory rate from 1 to 5.5? 11?

This will greatly limit the beacon cell. Ultimately however, have you asked Intel what they think (5100/5300?)? If clients can't handle that many beacons in the air, it is a client problem.... but then again that many beacons is sure to use a lot of bandwidth/utilization of the air.. so datarates may be a great adjustment anyway....

I seem to recall hearing of supplicants that can only keep X# of entries in its table.... so another symptom/problem could be that the supplicant is only recording a small number of the beacons... not sure how many windows ZC can handle

sin · ‎03-22-2010

We have 11mbit as lowest datarate on both 2.4 and 5 GHz. We are waiting from feedback from TAC, but I am thinking og going even higher say 24mbit. Unfortanly the is a global setting so chaning will affect all sites :-(

We have tryed asking Lenov, since we are using Lenovo laptop, but maybe it's worth a try asking Intel. I will have to try and find the best way to get contact them