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Wireless Protocols

Wireless networks form the backbone of modern connectivity, relying on a combination of physical infrastructure, standardized protocols, and frequency management to enable seamless communication. Understanding their architecture and underlying principles is critical for both offensive analysis and defensive mitigation. This section explores the physical and logical layers of wireless networks, focusing on 802.11 standards, frequency bands, and channel utilization strategies.

Physical Structure: Frequency Bands and Spectrum Allocation

Wireless communication operates on radio frequency (RF) bands, with the most common being 2.4 GHz (2.4–2.4835 GHz) and 5 GHz (5.15–5.85 GHz). These bands are divided into channels, each occupying a specific width (e.g., 20 MHz, 40 MHz, 80 MHz).

  • 2.4 GHz Band:
  • 11 channels (in the US/Canada) with 5 MHz spacing between channels.
  • Limited bandwidth (up to 54 Mbps in 802.11g) but widespread compatibility.

  • Susceptible to interference from devices like microwaves and Bluetooth.

  • 5 GHz Band:

  • 23 non-overlapping channels in the 5.15–5.35 GHz band (UNII-1) and additional channels in the 5.47–5.725 GHz band (UNII-2) with DFS requirements.
  • Higher bandwidth (up to 1.2 Gbps in 802.11ac) and less congestion.
  • Supports DFS (Dynamic Frequency Selection) channels (e.g., 5.25–5.35 GHz) that require radar detection to avoid weather interference.

Example: Use airodump-ng to monitor channel activity:

airodump-ng --channel 6 wlan0mon

Logical Structure: 802.11 Standards and MAC Layer Protocols

The 802.11 family of standards defines the logical architecture, including the MAC (Media Access Control) layer and PHY (Physical) layer. Key standards include:

  • 802.11b/g/n/ac/ax:
  • 802.11b: 2.4 GHz, 1–11 Mbps (obsolete).
  • 802.11g: 2.4 GHz, 54 Mbps (Wi-Fi 4).
  • 802.11n: 2.⅘ GHz, MIMO (Multiple Input, Multiple Output) for 300–600 Mbps.
  • 802.11ac: 5 GHz, MU-MIMO and OFDMA (Wi-Fi 5).

  • 802.11ax (Wi-Fi 6): 2.⅘ GHz, OFDMA, and improved efficiency for dense networks.

  • MAC Layer Protocols:

  • CSMA/CA (Collision Avoidance): Devices listen before transmitting to reduce collisions.
  • Beacon Frames: APs broadcast network information (SSID, channel) at regular intervals.
  • Authentication/Association: Clients authenticate via WPA3 or WPA2 and associate with an AP.

Example: Use iwlist to check supported channels:

iw list | grep -A 5 "Supported bands"

Channel Utilization: Optimization and Interference Mitigation

Efficient channel utilization is critical for performance. Key considerations include:

  1. Channel Width:
  2. 20 MHz: Minimal interference, ideal for crowded 2.4 GHz.

  3. 40/80/160 MHz: Higher throughput but increases interference risk.

  4. Channel Overlap:

  5. Adjacent channels (e.g., 1, 6, 11 in 2.4 GHz) must be spaced to avoid overlap.

  6. Use non-overlapping channels (e.g., 1, 6, 11) in 2.4 GHz.

  7. Hybrid Mode:

  8. 802.11ac supports 80+80 MHz channels (combined 160 MHz) for maximum throughput.

Example: Use airodump-ng to monitor channel activity:

airodump-ng --channel 6 wlan0mon

Key takeaways

  • Frequency bands (2.4 GHz vs. 5 GHz) dictate performance, range, and interference levels.
  • 802.11 standards define the logical architecture, with newer versions (e.g., Wi-Fi 6) improving efficiency via OFDMA and MU-MIMO.
  • Channel selection is critical for minimizing interference; prioritize non-overlapping channels and monitor utilization with tools like airodump-ng.
  • Understanding these fundamentals enables both offensive reconnaissance (e.g., channel scanning) and defensive hardening (e.g., optimizing AP configurations).