ZF7372 High Client Density issue

[wlangeek]

Hi Everyone,

I'm evaluationg the zf7372 as a potential replacement for some 2942's and 7363's that I use in a very high density environment. We typically budget 75-85 stations per radio on the current AP's we have. From the documentation on the 7372 it looks like it can handle 250 stations per radio and I'd really like to present a case for upgrading to reduce protocol overhead by reducing the number of AP's, but I need to get a proof working in the lab first.

I've setup a testing environment in one of my labs, and have only been able to get ~120 devices to associate before the AP stops accepting associations. The logs on the attached ZD1100 show "User [DEVICE_MAC] fails to join WLAN [WLAN_NAME] from AP[AP_MAC]"

I've done a little more snooping using some of the tools I have and it appears that once I hit this ~120 device limit, the newer devices are able to associate, but are immediately (within ~7ms) sent a deauth frame. This testing environment is an open/WEP64 wlan, so I don't think I'm running into memory or other resource issues on the AP during the negotiation phase, but I could be wrong. I've looked at the AP logs and they show that the AP has plenty of memory remaining (60+MB)

I'm running 9.6.0.0.267 on a zf1100 with the same release on the AP.

The logs on the AP show the following errors once I reach the ~120 device range and start to see the deauth frame response to new clients:

Aug 12 23:35:04 RuckusAP user.info kernel: tac_set_station_key(): tac_set_station_key: new key failed
Aug 12 23:35:04 RuckusAP user.info kernel: net80211_tac_cfg_sta_add(): add station {DEVICE_MAC} session key,failed cipher = 2
Aug 12 23:35:04 RuckusAP user.info kernel: tac_set_station_key(): tac_set_station_key: new key failed
Aug 12 23:35:04 RuckusAP user.info kernel: net80211_tac_cfg_sta_add(): add station {DEVICE_MAC} session key,failed cipher = 2
Aug 12 23:35:04 RuckusAP local2.err syslog: Failed add station in processing MSG_MOBILE_CFG_REQ

I've tried disabling all the features I can to narrow down the issue, but I haven't had any luck (background scanning on/off, dropping multicast packets on/off, client load balancing on/off, client fingerprinting on/off, only one wlan active on the AP, etc). I've also ensured that the device limits are set higher than 120 clients so I don't believe I'm running into an issue there. I also don't see any warnings about reaching 90%+ of the AP's capacity as I generally do when I approach the limits on a 7363 device which also leads me to believe that it's a software issue and not a misconfiguration.

Anyone have some pointers on what might be going on here? It's starting to look like a bug in the AP firmware somewhere in the key management subsystem to me.

~WlanGeek

[jon_prouty]

I do live in the USA, probably qualifies as happy land compared to most!

Thanks for spouting off the last few months of webinars for everyone. Definitely needed that...

And after all of that the fact still remains that fewer clients per radio will give you better overall performance.

Thanks though!

[keith_redfield]

I love a vigorous debate and see both sides - but so much depends on the environment. I suspect that local conditions differ quite a lot between the different points of view.

I should try to get a screenshot of the EMF in our support lab and post it here. It's appalling (we're next door to the QA lab). My Mac Pro can barely display all the SSIDs (all rogues to boot). Yet client connections are amazingly stable and responsive. Well, here's the view from my desk where I have only plugged in once (due to a quickly-resolved RADIUS bug. Names pixelated to protect the innocent - but who is Video 54?)



And if you can't buy Ruckus...there is [maybe] another answer

http://www.lessemf.com/paint.html

;) [No endorsement - I've no idea whether this stuff works.]

[eizens_putnins]

I like how you stick to your opinion. There is nothing personal in my comments -- please don't feel offended in any way. I like that you have looked on last Ruckus webinars, I had merely time to look on some recordings only, unfortunately, but I like them -- Ruckus guys as usually know staff quit well and provide it in easy understandable form, which is especially important for new users.
And I have to completely agree -- one client sitting on an AP will have the best performance possible, all for himself. As well as 100 clients distributed to 10 APs, without any interference, would obviously have better performance than 100 clients on 2 APs. This is OK and completely reasonable, and is very correct with lightly loaded networks and clean areas.
Problem is that you usually just never get such situation any more. And if you have 200 uniformly (and heavily) loaded clients in compact area (say, 50x50 m2) and have to decide if you have to use 10x or 2-3x APs, usually 2-3 good APs will actually provide much better overall performance. It is not simple to decide, anyway, as in some conditions it may also be completely opposite -- it may be better having more APs.
Simple explanation is -- you have 3 non-overlapping channels on 2.4Ghz, so adding more APs in same area will just divide same resources between more AP and add a lot of overheads. But as usually, the simple explanation is not correct, as connection speeds for clients have huge impact as well as other factors.
Even more complicated it becomes with Ruckus, as these APs use different antenna patterns for downstream and upstream traffic, and transmission becomes very asymmetric. There is no simple answer any more.
Anyway, having more client supported on AP is usually a huge benefit. This is a typical limitation for SOHO devices, we had replaced during last years a lot of networks in hotels, based on low capacity gear, which became unusable in current conditions.
Most obvious it is in 2,4 GHz, of cause, but 5GHz is getting close, and a lot of enterprise laptops still have 2,4GHz-only cards in our country.
If area is compact and not divided by metal walls, you'll have 3-4 APs on the same channel, you'll have also neighbors, and performance can be actually much less than expected. But it depends on many things, including traffic pattern for clients.
Also some APs would work better in such situation than others (it depends on antennas, primary, but also on hardware and software).
Typical problem recently became that you have a lot of passing-by clients (smartphones), which actually don't want to use your network, but try to connect to it automatically anyway. They can make your AP tables full, if it is not designed to handle it. I had such experience in public areas (especially with open SSIDs), with previous generation Cisco and HP equipment, and the only solution 2 years ago was to replace this gear by working solution from different vendor (surprise?).
We have 3 years old installation with 10x APs producing 200GB traffic per day traffic (and there is about 80 rogue APs around them). Number of associated clients comes to 100 per AP twice a day now, so customer plans to upgrade system.
By the way, in USA you must have even more problems with interference on 2.4GHz as more power and less channels are allowed, but you have much more territory, probably. Also for headquarters with a huge parks around it is really possible to discard any external interference, and have 802.11n in green mode.
It is not the case in our country.
In our office building, there are about 40 companies on 5 floors, even smallest having at least one Wi-Fi AP, and we have 3 multi-tenant buildings in vicinity with a lot of home equipment. Our office list of rogues is 60+ APs, some with RSSI -25dbm. And this is a typical situation, not an exception.
We have just learned in the field during last 3 years that Wi-Fi planning is much more complicated and no webinars or handbooks help much -- you need practical experience, good equipment, you have to try different solutions and you'll get some problems anyway.
There is no going back of cause, and we'll figure how to get most of 802.11ac soon..
Life is life...
Have a good day and as much free of interference channels, as possible!
.

[jon_prouty]

I'm not offended and not trying to offend, the internet is hard to relay exactly what you are trying to say. Definitely being aware of your environment with your wifi systems is key which Eizens has demonstrated he is well aware of his environments! I work in education so in most cases they get to control all the airspace around them since a lot of the schools I work with are in unpopulated areas. I have worked with schools in some dense areas and neighboring rf is something you definitely have to be aware of when designing the system. I did one floor of a skyscraper in Seattle a couple years back and that was a fun system to design. I also had to negate a sales guys deal one time when he was trying to sell a 2.4 bridge to hook up two sites in Seattle that were separated by several apartment complexes, there was only just over a hundred ssid's in between the sites in the 2.4 range.

SNR is key in these super dense environments which is why the ruckus ap's do so well by having the adaptive antennas to give the client the best signal quality possible. Having an adaptive controller setup that can adjust channels and power levels of the wifi system to mitigate interfering rf is key as well.

I wish I could leave the 2.4 airspace behind as well but education is full of legacy clients. They will get there one day but until then you always have to use that frequency as your base for installations as it has the larger rf footprint and the fewest channels available.