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AP's in different VLANs, serving several SSIDs



Question to more advanced users, really.


I have 2 5508 series WLC controllers serving around 160 AP's, all of them 1141 series. Those have IP's assigned from one DHCP server, but it was setup so that I have 3 separate scopes each serving 64 IP. All of those AP's have same 7 SSID's.


My problem is that I'm observing constant fluctuations of power from AP's - it's like they fight for airwaves. At one point have -70dB from AP, after minute or two it's droping to null and other AP ramps up from null to full power. After another time cycle they reverse power levels.
Is a fact that some neighbouring AP have IP from different subnet can affect coverage or start contention between AP's?? Or fact, that they are connected to integrated WLC's makes them 'understand' that AP - even if it has IP from different subnet - is friendly and issue is coming from not enough distance between AP? Where to look for clues?

Have full admin rights to system, but no experience in troubleshooting wireless networks on this level.


Re: AP's in different VLANs, serving several SSIDs

Hi Robert,


As long as the access points connect to the same WLC or if you have multiple WLC's that are part of the same mobility group and RF domain the WLC/s will be aware of the neighbouring AP's despite being on different IP's.


The WLC uses Radio Resource Management to increase or decrease signal levels of the AP's, this can be for various factors, for example, neighbouring AP's that are close to each other or environmental elements that may affect the attenuation of the AP's signal.


The best thing to do is investigate the issue on site and use a wireless survey tool such as Ekahau Site Survey and verify what is the RF health is, there could be co-channel interference in the area. Also observed the environment during the period when you see signal levels drop, there could some activity happing in the area that may affect your AP's signal.


If your WLC's radio configuration settings are set on default, you also might need to adjust this based on how your AP's are deployed, this is more advanced though.

Hope this gives you better clarity.


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Re: AP's in different VLANs, serving several SSIDs

Hi Jurgens,


Thanks for reply, it does removes one of potential problems - having 3 VLANs for APs..


As per rest of them it's time consuming to do physical sweep - are there any tools within WLCs that I can use??  Metrics that can show one way or another that this is issue with APs too close to each other etc?

Re: AP's in different VLANs, serving several SSIDs

If you want to narrow it down, you can view the interference levels, top users per AP count. Depending on what version code you running on your WLC, you can access the "home" page. I've attached a screenshot of an example where you can go and view the statistics. 


Another powerful tool to use is Cisco Prime, if you have VM capacity, you can fire up an instance of this and link your WLC up with it. It comes with a 90day trial license for you to use currently version 3.3 and 3.4 are recognised by Cisco as a stable release, depending on the WLC code you are running. Prime will allow you to go back in time when users complained about issues and you can see any events that could have occurred the time of the event. 

When it comes to monitoring and troubleshoot Cisco Wireless networks, there is nothing else out there that comes close to it as Cisco Prime is getting more access to the WLC than other monitoring software such as SolarWinds for example.


When you narrow down the area of your issue, I will still recommend you go physically there and troubleshoot further. With wireless, it is key to interact with users and find out their experience with wireless, you may think everything is ok and when you interact with them you will get different feedback, sometimes the issue is not related to wireless, could be DHCP, DNS or firewall policies, from the user's point of view they see it as a wireless issue.


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Re: AP's in different VLANs, serving several SSIDs

As you are using 7 SSIDs (always a bad idea), make sure you have all rates below 18 Mbps disabled for the 2.4 and 5 GHz, or your beacons eat up most of the available airtime.
Then make sure that both WLCs are in the same Mobility Group and that the connection status is UP. This is absolutely important for all roaming and I think RRM features.
As Jurgens already suggested, put all APs into the same L2 vlan if possible.
Also make sure to run the latest WLC software that still supports your 1140.

Re: AP's in different VLANs, serving several SSIDs

Hi patoberli,


My WLC's were allowed to run out of support contract before I've inherited them, currently on version 6.0.199. As far as I know I cannot get newer software without support contract?

Disabled rates, that's great advice, mobility group is up and running.

L2 will take some time to get done, especially if I have to do new vlan for all of them.

Any other advices? I have limited knowledge of WLC so any reputable resource website explaining basics would be appreciated as well.. :)


Re: AP's in different VLANs, serving several SSIDs

Yes, get a service contract. Your used software has various known security issues and is already > 7 years old.
See here for some of the known security issues:
You might even very soon get certificate issues, because of outdated (> 10 years) certificates on your APs.
See here:
Please note, your version 6 is not listed, because it was probably already End of Life when this field notice was written. I'm not 100% sure if your APs are affected by this though, you might get lucky.

In any case, I'd get a software contract (including hardware replacement warranty) and upgrade to Please note, you will have to do the upgrade in several steps, as you are already many versions behind. You might even require a FUS upgrade.
Release notes:
FUS upgrade: (only needed if your shown versions are older, upgrade will take around 30 minutes per WLC)

It looks like you can do it in two steps, first upgrade to (wait until all APs have upgraded and are connected again, then wait some 15 more minutes) and secondly to If a FUS upgrade is required, do that first, or your WLC might not anymore boot because of the CF Card error.
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