Divergent Dynamics CEO Devin Akin named toTWW Top 100 Wireless Experts for 2014
www.todayswirelessworld.com/top100/
Devin K. AkinCEO, [email protected]+1.404.437.6006
Devin Akin
15+ years of Innovative Experience in Wi-Fi
Co-founder/CTO, The CWNP Program (cwnp.com), 2001-2009
Chief Wi-Fi Architect, Aerohive Networks 2009-2013
Network Architect, Evangelist, Author, Speaker, Teacher, Blogger
Advisor to most Wi-Fi manufacturers at some point since 2001
Divergent Dynamics, Inc.
Wi-Fi Advisory & Consulting
Wi-Fi Performance Diagnostics & Optimization
Wi-Fi Training Services
ADDRESSING THE
TOP WIFI COMPLAINTS
It just has to work!
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WHAT WIFI COMPLAINTS DO YOU TYPICALLY GET?
• The WiFi is too slow
• I keep getting disconnected
• I can’t roam
• I can’t connect to the wireless network
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WHAT ARE THE CAUSES BEHIND THESE COMPLAINTS?
• Misconfiguration– WNMS, Controllers, and/or Access Points
– Clients
• Coverage
• Capacity
• Co-Channel Interference– Your network
– Neighboring networks
– Rogues
• Non-WiFi Interference– Persistent sources
– Transient sources
• Security breaches and attacks
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FINDING ROOT CAUSE IS COMPLEX
Complaints Causes
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Slow
Can’t
Connect
Get
Disconnected
Can’t Roam
AP misconfigured
Too many APs on channel
Interferers are present
Too many SSIDs broadcasting
Neighbor AP on same channel
Too many users on same AP
User’s client misconfigured
Client connected at slow rate
AP cell too big
Legacy 802.11b clients present
Excessive Retries on channel
Too many users on channel
AP cell too small
No secondary AP coverage
Poor SNR
Too many simultaneous Tx
FINDING ROOT CAUSE IS COMPLEX
Complaints Causes
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Slow
Can’t
Connect
Get
Disconnected
Can’t Roam
AP misconfigured
Too many APs on channel
Interferers are present
Too many SSIDs broadcasting
Neighbor AP on same channel
Too many users on same AP
User’s client misconfigured
Client connected at slow rate
AP cell too big
Legacy 802.11b clients present
Excessive Retries on channel
Too many users on channel
AP cell too small
No secondary AP coverage
High channel utilization
…AP misconfigured
Client misconfigured
Poor SNR
Too many simultaneous Tx
FINDING ROOT CAUSE IS COMPLEX
Complaints Causes
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Slow
Can’t
Connect
Get
Disconnected
Can’t Roam
AP misconfigured
Too many APs on channel
Interferers are present
Too many SSIDs broadcasting
Neighbor AP on same channel
Too many users on same AP
User’s client misconfigured
Client connected at slow rate
AP cell too big
Legacy 802.11b clients present
Excessive Retries on channel
Too many users on channel
AP cell too small
No secondary AP coverage
High channel utilization
KEY POINTS
• WiFi is location-dependent. Need portable tools to troubleshoot.
• WiFi uses a time-shared medium… the channel.
• RSSI is important, but SNR is more important.
• Critical KPIs include channel airtime utilization, SNR, retry rates.
• Client-side visibility is priceless.
• Every wireless network uses a wired network. Check wired services!
• The right tools for the job makes all the difference.
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SO LET’S LOOK AT EACH COMPLAINT AND HOW IT CAN BE ADDRESSED…
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WHAT TO LOOK FOR
• How many APs on the channel (CCI)?
• Airtime utilization of the channel for WiFi devices
– Are there legacy clients present?
• Airtime utilization of the channel for non-WiFi devices
– Are there any non WiFi interferers on that channel?
• What AP is the customer connected to, and what rates are
supported (in each direction)?
• At what rate is the customer connected?
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WHAT DAVE THE IT TECH DID
• Grabbed his AirCheck G2 Wireless
Tester and went to the location of the
user.
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WHAT DAVE THE IT TECH DID
• Found the user’s connection on his
AirCheck G2, and identified its
channel.
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WHAT DAVE THE IT TECH DID
• Checked the channel and found too
many APs on it.
• Corresponding 802.11 utilization
was high.
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WHAT DAVE THE IT TECH DID
• Drilled down to the APs on the
channel and saw many neighbor
network APs.
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WHAT DAVE THE IT TECH DID
• Viewed other channels and found
one much less used.
• Moved the AP to that channel.
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WHAT DAVE THE IT TECH DID (V2)
• Checked the channel that the
client was on.
• Found 2 APs on the channel;
didn’t seem too bad
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WHAT DAVE THE IT TECH DID (V2)
• Checked channel utilization and
saw it was very high
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WHAT DAVE THE IT TECH DID (V2)
• Checked the APs on the channel and
found one was not familiar.
• He located it.
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Where you at,
you little booger?
I’m on your trail!
WHAT DAVE THE IT TECH DID (V2)
• Found a rogue AP that was
transmitting large files. One AP and
client caused over-utilization of the
channel.
• Removing the AP killed two problems
with one swipe - Score!
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XDie rogue, die!
WHAT DAVE THE IT TECH DID (V3)
• Checked the channel and found
802.11 utilization was high.
• Could not determine why
• Notified Tom the engineer
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No idea. Hey Tom!
WHAT TOM THE ENGINEER DID
• Went to the location of the problem
with the AirMagnet WiFi Analyzer
PRO
• Scanned the channel
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I’m glad I still had
this laptop with an
ExpressCard
adapter slot…
WHAT TOM THE ENGINEER DID
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• Saw high channel
utilization, and most of it
was low speed
transmissions
• Saw high utilization due to
Control Frames, and
within that, RTS and CTS
frames
DIAGNOSIS
• Excessive RTS/CTS frames often due to too many clients on a channel (not just an AP; it is the channel that is shared)
• Consider
– Client load balancing
– AP transmit power and cell size (clients connecting from too far away)
– Another AP for capacity (if another channel is available)
– iOS device use RTS/CTS even when unnecessary
– Upgrading older client devices
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WHAT TO CHECK FOR
• Are there interference sources present?
– Check signal levels and duty cycles
– Is WiFi congestion high?
• Weak SNR at client location
• Is the infrastructure configured properly/optimally?
– Is Band Steering being used? How well is it working?
– Are there SNR or RSSI thresholds for active scanning responses?
– Is RRM enabled? Is it working to your satisfaction?
• What roaming protocol is in use (OKC, Pre-Auth, Voice-Ent, etc.)?
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WHAT DAVE THE IT TECH DID
• Grabbed his AirCheck G2 Wireless
Tester and went to the location of the
user
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WHAT DAVE THE IT TECH DID
• Found the AP that the user connects
to, and identified its channel
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WHAT DAVE THE IT TECH DID
• Saw non-802.11 WiFi channel utilization
was high. Immediately knew there was a
interferer issue and notified Tom the
engineer
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Sorry to keep
bothering you Tom…
WHAT TOM THE ENGINEER DID
• Grabbed his AirMagnet Spectrum XT
and identified the interference source
– Only periodic transmissions
– But duty cycle = 99% and across all
2.4GHz band
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WHAT TOM THE ENGINEER DID
• Located the interference source
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WHAT TOM THE ENGINEER DID
• Depending on the interference source:
– Removed it
• For unauthorized or unnecessary devices
– Changed the WiFi channels around it
• For embedded devices like microwave ovens and security cameras
– Move the AP or increase AP power to increase SNR
• For low-power devices like sensors
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WHAT TO CHECK FOR
• Secondary AP coverage
• AP cell sizes too big, Tx power too high
• Client overload on an AP
• AP misconfiguration
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WHAT DAVE THE IT TECH DID
• Grabbed his AirCheck G2 Wireless
Tester and successfully connected to
the network
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WHAT DAVE THE IT TECH DID
• Performed a roaming
test. Roaming failed
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WHAT DAVE THE IT TECH DID
• AirCheck G2 indicated the network had
mixed security types. This is a
misconfiguration of an AP.
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WHAT DAVE THE IT TECH DID
• Immediately went to the list of
APs on the network. Saw the
AP he needed to roam to was
set for the wrong security type.
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WHAT DAVE THE IT TECH DID
• Fixed the AP security configuration issue, and roaming was
restored
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WHAT TO CHECK FOR
• Network availability
• Proper signal coverage and SNR
• Proper access point configuration
• Proper client configuration
• Channel utilization and interference
• Network services availability: DHCP, DNS, gateway router
• Security incidents
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WHAT TOM THE ENGINEER DID
• Grabbed AirMagnet WiFi Analyzer PRO
and went to the location of the problem.
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WHAT TOM THE ENGINEER DID
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• Viewed AirWISE® alerts
and immediately saw a
DoS attack
WHAT TOM THE ENGINEER DID
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• Selected the source and went to
the Find screen.
• Located and disabled the
attacking device.
• Network connectivity was restored
STEP-BY-STEP TROUBLESHOOTING TREE
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WIFI TOOLSET FOR TROUBLESHOOTING
FOR THE NETWORK
TECHNICIAN
FOR THE NETWORK
ENGINEER
AirCheck G2
Wireless TesterAirMagnet
Spectrum XT
AirMagnet WiFi
Analyzer PRO
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