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CCNA Wireless Study Notes

·672 words·4 mins
Networking WiFi Cisco
Author
Craig Bruenderman

WLAN Fundamentals
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Ad Hoc Mode
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Ad Hoc Mode
Independent wireless devices building a wireless network without any other infrastructure
BSS
Basic Service Set - Area in which a given device can be reached wirelessly
IBSS
Independent Basic Service Set - Setup without any other infrastructure, ad hoc

Infrastructure Mode
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Infrastructure Mode
Wireless network built using access points
AP
Access point
BSA
Basic Service Area (cell) - Area that an access point effectively covers
SSID
Service Set Identifier -
DS
Distribution System - Infrastructure linking wireless system to all other network resources
WLC
Wireless LAN Controller -
ESS
Extended Service Set - When you have two or more APs on different channels, advertising the same SSID, working in conjunction via a WLC
Roaming
Seamless movement between acces points
  • Wireless is always half-duplex

Standards and Regulations
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  • Layer 1 and Layer 2 protocols
    • IEEE 802.11 working group for Wireless LANs
    • Study the apps and uses of WLANs, publish protocols, modulation, frequency, framing, physical
  • Interoperability testing
    • Wi-Fi Alliance

Regulatory Organizations
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  • FCC - Federal Communications Commission
    • How much power or which frequencies
  • ETSI - European Telecommunications Standards Institute
  • TELEC - Telecom Engineering Center (Japan)
  • BRAI - Broadcasting Regulatory Authority of India

RF Fundamentals
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Frequency
Speed at which the wave repeats, measured in cycles per seconf (Hertz)
Wavelength
How wide is one cycle
Amplitude
Energy of waveform
RSSI
Received Signal Strength Indicator
  • For RSSI, closer to zero is better

Interference
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Free Path Loss
Normal atmospheric attentuation
Scatter

  • Physical obstacles absorb RF

  • Reflection

  • Multipath results in signal cancellation

    • Upfade, downfade, or cancellation, depending on phase

  • Fade

  • Long-range atmosphere refraction

  • RSSI minus noise = Signal to Noise Ratio (SNR)

SNR
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  • Signal - Noise floor
  • E.g., -70 - (-95) = 25
  • Shooting for SNR of 20 or better

dBs and Watts
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  • Decibel is a comparison

  • 0dBm = same

  • 10dBm = 10x

  • -10dBm = 0.1x

  • 3dBm = 2x

  • -3dBm = 0.5x

Antennas
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  • H-Plane - Top down view, horizontal plane
  • E-Plane - Side view
EIRP
Effective Isotropic Radiated Power

  • FCC is 36dBm

  • Antenna gain (dBi) - Focusing energy over a certain area

  • Dipole reference (dBd), add 2.15dBi gain

  • Unidirectional

  • Omnidirectional

Frame Types
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  • CSMA/CA - Collision avoidance
  • WiFi is half-duplex

3 Categories
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  • Management Frames
    • Beacons, Probes, Association, Authentication
  • Control Frames
    • RTS - Request to Send
    • CTS - Clear to Send
    • ACK - Confirmation of frame delivery
  • Data Frames

Slot times
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  • 802.11b - 20us
  • 802.11a,g - 9us
NAV
Network Allocation Vector - Duration during which no one else can send.
SIFS
Short Inter Frame Space. Between 10-16us
DCF
DIFS
Delay Inter Frame Space

Frame Flow
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WLAN Disruptors
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WLC and AP Concepts
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  • Split MAC
    • AP runs radio, sends ACKs & beacons, responds to probes
    • Controller does authentication and authorization, dis-associations, policy
CAPWAP
Control and provisioning for wireless access points

802.1x and EAP Concepts
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WLAN Security
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Supplicant
Provides credentials
Authenticator
Requests credentials
Authentication Server
Authenticates credentials

  • EAP - Extensible Authentication Protocol

    • LEAP - Lightweight EAP
    • FAST - EAP Flexible Authentication via Secure Tunneling
    • PEAP - Protected EAP
      • Authenticator has certificate only
    • EAP-TLS - Transport Layer Security
      • Both supplicant and authentication server have certs

  • Symmetrical - Same key used to encrypt and decrypt

  • Assymetrical - Key pair, one to encrypt, one to decrypt

    • Public key
    • Private key

  • Digital certificate contains entity public key

  • Certificate Authority

WLAN Troubleshooting
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Rogue APs
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  • De-auth attacks

  • Radio Resource Management (RRM)

  • Clean Air

    • Air Quality Index

  • wIPS

Frequencies and Protocols
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  • ISM - Industrial, Scientific & Medical band
    • 2.4Ghz, 3 non-overlapping channels
  • UNII - Unlicensed National Information Infrastructure
    • 5Ghz,
  • Non Overlapping Channels
  • Channel Bonding
  • 802.11 Protocols
    • 802.11a
    • 802.11b
    • 802.11g
    • 802.11n
    • 802.11ac

MIMO & 802.11n & 802.11ac
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  • MIMO - Multiple Input Multiple Output
    • Multiple antennas
  • MU-MIMO - Multiple User Multiple Input Multiple Output
  • Transmit x Receive : Spatial Streams
  • Beamforming
  • MRC - Maximal Ratio Combining

Design Considerations
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  • Applications that will be used
    • Real-time - voice, video
    • Non real-time - email
  • Facility details, clients, signals, APs

Surveys
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  • Predictive
  • Pre-survey (passive and active)
  • Post-survey