WiFi & you.

“Clicker” test

How many of you connect to WiFi @ UNLV with:

1. 1 device
2. 2 devices
3. 3 devices
4. 4 or more devices
5. What is this Wi-fi you speak of?

UNLV Wireless usage (October 2013)

• 53,081 Unique devices
• 22,395 Devices/day
• 900Mb of 1.4Gb per second to internet is WiFi
• 451,521 Authentications/day

​

• 70% campus covered
• Thomas & Mack (possibly).
• Most classroom spaces coming.
• Closer to 90% coverage by this time next year
• Likely increase by 50% ‘devices’

​

Quick overview - 802.11 Channels*

2.4GHz (802.11B/G/N) - Only 3 ‘usable’ channels

* usa

CCI is better than ACI

5GHz (802.11A/N/AC) - 24 Channels

In the US we have up to 11 non-overlapping channels to choose from, for 802.11b/g/n (2.4ghz)

1. True

​

• False

WiFi is a Shared Medium (like a hub)

• Half duplex (think 2-way radio)
• I won’t talk if someone else is talking
• Channel can only be used by one device at a time.
• Speed matters...it’s all about “Air Time”

Analogy: *Mike screaming like an idiot (in English)*

• If I talk really slow, the conversation takes long!
• If I talk really loud, I’ll disturb the next room
• this is called: “Data Rate”. This is what you see when looking at “connection properties”.

Why should we encourage adoption of 802.11ac for a low speed device like a smart phone?

A. We don’t care, a smartphone would rarely need gigabit wireless speeds

​

B. Faster speeds mean less air time which means the channel is free for others to use

​

C. Youtube videos look better with 802.11ac

Most common problems - in order.

1. Interference

​

1. Drivers

​

2. 802.1X Supplicant configuration

Most Common Interference Sources

• Rogue AP’s:
• Soho routers/MyFi/Ad-hoc’s/printers/WiFi-direct/ Tethering phones
• Microwaves
• Cordless phones
• Non-wifi wireless Camera’s (ie Baby Monitor)
• Bluetooth
• X-Box controllers
• Radar (5GHz only)
• Our own WiFi?

802.11 Interference

Rogues/ad-hocs/MyFi’s etc.

Rogues

...and why they suck are such a problem.

RF contention for Air Time

• Support low ‘data rates’ and 802.11b

​

• Operate on overlapping 2.4GHz channels
• A rogue on channel 3 severely impacts our AP’s on both channels 1 & 6 (ACI worse than CCI)

​

• Big security concerns -- extend our wired cable plant to the parking lots.
• Even if secured with latest standards like WPA2-Personal (ie not WEP), they are vulnerable. google: wps vulnerability

Air Time Example with only 1 client!

Virtually all rogue devices support 1Mb data rate.

​

This example is a printer (ad-hoc).

​

​

​

“race to the bottom”:

More rogues = more noise = less SNR = higher retransmit rates = more rate-shifting (down) = RF consumed = WiFi Broken.

Rogue’s consume RF air-time, severely impacting UNLV WiFi performance

​

​

1. True

​

• False

​

Rogues can use channel 8, since UNLV WiFi only uses channels 1, 6 & 11.

​

​

1. True

​

• False

Non-802.11 Interferers

...and why they also suck are such a problem

They do not care about 802.11

• They ignore the rules of “is it ok to talk now?”

Analogy: *Mike screaming like an idiot in a make believe language*

• Like holding down the “talk” button on the 2-way radio...constantly.
• They consume the RF ‘channel’.
• This is called “Channel Utilization” or “Duty-cycle”

​

• Even if not ‘consuming’ the channel, WiFi devices can not understand the ‘make believe language’
• This is called “demodulation”.

​

Cordless phone -- 100% CU

When something like this occurs, WiFi completely breaks.

​

*Cordless phone pictured here is non-DECT. DECT Phones operate at 1.8/1.9GHz, meaning no WiFi interference.

Drivers

Are they up to date yet?

Mostly affects Linux & Windows

• Windows update does NOT update your drivers

​

• Device Manager-->Get chipset information--> Go to manufacturers website-->Download latest-->Call me in the morning (or don’t).

​

• This fixes TONS of problems. Association, 802.1X (WPA2) etc. Please do this prior to escalation!

​

802.1X

This is what WPA2-Enterprise uses.

The Supplicant

• Painful: 15 - 30 clicks

​

• Helpdesk = first line of defense against this issue.

​

• http://wireless.unlv.edu/secure (learn it, love it, live it)

​

• Improperly configured means:
1. No authentication (can’t get to facebook)
2. Slow authentication (can’t get to facebook fast enough)
3. Insecure (I’m on facebook, but so is the guy next to me...as me)
4. A solution exists, but we have not purchased it (yet?)

​

• Management frames are un-encrypted (802.11w will solve this)
• autoconfigured/misconfigured supplicant = clients vulnerable. Google: fakeradius

​

What we do @ infrastructure level

Dual-band clients often choose 2.4GHz instead of the much less crowded 5GHz

Non-802.11 interference will occur, no matter how hard we try to eliminate it.

​

With only 3 2.4GHz channels, how do you cover a classroom building requiring 100+ AP’s.

The rogue ap’s are everywhere! How can you locate them?

​

I need my Burrito!

Band-Select. If AP see’s client is capable of 5GHz, it ignores first 3 association requests on 2.4GHz.

“Clean-Air”. About 50% of our AP’s can detect devices (like video cameras, microwaves etc.) and move away from those channels affected.

​

Directional antennae. Turn down Tx power of AP’s. Raise minimum mandatory data-rate. This reduces the cell-size.

​

In many cases we can pinpoint location (~10 meters accuracy) on a floorplan. Fluke air-check when on-site.

Education on the topic of interference goes a long way. Try to set an accurate expectation...”that burrito is destroying your WiFi!”

Tools you can use

Android:

• WiFi Analyzer
• IPerf - test2.net.unlv.edu

iPhone:

• Bars?

OSX:

• alt-click the wifi icon
• wifi-diagnostics/utilities
• /var/log/wifi.log

Linux:

• /etc/wpa_supplicant/wpasupplicant.conf

Windows:

• inSSIDer

How you can help

• aforementioned drivers & supplicant

​

• Report improper antenna orientation to Help Desk *show example*

​

• Inform your customers about the problems with rogue wireless

​

• Make sure UNLV Wireless is avail. in the area you’re troubleshooting (hint: non-OIT wifi exists w/ ‘UNLV’ in the SSID)

​

• Disable printer wireless

​

​

I found this presentation

1. Useful - Thanks for the info.

​

• Somewhere in the middle.

​

• Useless - 1 hour I will never get back

​

I would like a presentation on

1. High-density WiFi design

​

• 802.1X & the EAP Process

​

• Using tools like Fluke Air-Check to diagnose issues.

​

• Why 802.11n & 802.11ac are so much faster

​

• No more, just let me out of here.