Wireless_networking

Chapter 17: Wireless Networking

17.1 Introduction to Wireless

Wireless networking uses radio waves to connect devices without cables.

                    Wireless Fundamentals
+------------------------------------------------------------------+

Frequency Bands:
+------------------------------------------------------------------+
|  Band        | Frequency      | Use                             |
|--------------|----------------|---------------------------------|
| 2.4 GHz      | 2.4-2.4835 GHz| WiFi, Bluetooth, IoT         |
| 5 GHz        | 5.15-5.85 GHz | WiFi (high speed)            |
| 6 GHz        | 5.925-7.125 GHz| WiFi 6E (new)               |
| 60 GHz       | 57-66 GHz      | WiGig (very high speed)      |
+------------------------------------------------------------------+

Key Concepts:
+------------------------------------------------------------------+
|  - SSID: Network name                                           |
|  - BSSID: Access Point MAC address                              |
|  - Channel: Frequency within band                              |
|  - Bandwidth: Data capacity                                     |
|  - Signal Strength: Measured in dBm                            |
+------------------------------------------------------------------+

Signal Strength (dBm):
+------------------------------------------------------------------+
|  -30 dBm | Excellent | Strong signal, close to AP              |
|  -50 dBm | Good     | Reliable connection                      |
|  -60 dBm | Fair     | Usable but may drop                     |
|  -70 dBm | Poor     | Intermittent connection                  |
|  -80 dBm | Weak     | Barely usable                          |
|  -90 dBm | No signal| Not usable                             |
+------------------------------------------------------------------+

+------------------------------------------------------------------+

17.2 WiFi Standards (802.11)

                    WiFi Standards
+------------------------------------------------------------------+

| Standard | Year | Freq    | Max Speed | Range (indoor) |
|----------|------|---------|-----------|----------------|
| 802.11a  | 1999 | 5 GHz   | 54 Mbps   | ~35m          |
| 802.11b  | 1999 | 2.4 GHz | 11 Mbps   | ~35m          |
| 802.11g  | 2003 | 2.4 GHz | 54 Mbps   | ~38m          |
| 802.11n  | 2009 | 2.4/5   | 600 Mbps  | ~70m          |
| 802.11ac | 2013 | 5 GHz   | 3.4 Gbps | ~35m          |
| 802.11ax | 2021 | 2.4/5/6| 9.6 Gbps | ~30m          |

WiFi 6 (802.11ax) Features:
+------------------------------------------------------------------+
|  - OFDMA: Multiple users share channel                          |
|  - MU-MIMO: Multiple users, multiple outputs                   |
|  - 1024-QAM: More data per transmission                        |
|  - BSS Coloring: Reduce interference                           |
|  - Target Wake Time: Better battery life                      |
+------------------------------------------------------------------+

WiFi 6E:
+------------------------------------------------------------------+
|  - Adds 6 GHz band                                             |
|  - Less congestion                                             |
|  - Higher speeds                                               |
+------------------------------------------------------------------+

Channel Width:
+------------------------------------------------------------------+
|  Standard | Channel Widths (MHz)                                |
|-----------|---------------------------------------------------|
| 802.11n   | 20, 40                                         |
| 802.11ac  | 20, 40, 80, 80+80, 160                        |
| 802.11ax  | 20, 40, 80, 160                                |
+------------------------------------------------------------------+

+------------------------------------------------------------------+

17.3 WiFi Channels

                    Channel Allocation
+------------------------------------------------------------------+

2.4 GHz Channels:
+------------------------------------------------------------------+

Channel | Center Freq (MHz) | Non-overlapping
--------|-------------------|----------------
1       | 2412              | Yes
6       | 2437              | Yes
11      | 2462              | Yes

Note: 2.4 GHz channels overlap. Use 1, 6, 11 for minimal interference.

2.4 GHz Channel Overlap:
+------------------------------------------------------------------+

      Ch1  -----------
               Ch2
                    Ch3
                         Ch4
    ... and so on

    Ch1(2412)   Ch2(2417)  Ch3(2422)  Ch4(2427)
    |-----------|-----------|-----------|
              22 MHz bandwidth per channel

+------------------------------------------------------------------+

5 GHz Channels (U-NII):
+------------------------------------------------------------------+

| Band  | Channels | Freq Range   | DFS Required |
|-------|----------|--------------|--------------|
| U-NII-1| 36-48   | 5.15-5.25 GHz| No          |
| U-NII-2A| 52-64   | 5.25-5.35 GHz| Yes         |
| U-NII-2C| 100-144 | 5.47-5.72 GHz| Yes         |
| U-NII-3 | 149-165 | 5.73-5.825 GHz| No         |

Common 5 GHz Channels: 36, 40, 44, 48, 149, 153, 157, 161

+------------------------------------------------------------------+

+------------------------------------------------------------------+

17.4 Wireless Security

                    WiFi Security Protocols
+------------------------------------------------------------------+

| Protocol | Encryption | Security | Status   |
|----------|------------|----------|----------|
| WEP      | RC4 64/128 | Weak     | Deprecated |
| WPA      | TKIP      | Moderate | Deprecated |
| WPA2     | AES-CCMP  | Strong   | Standard  |
| WPA3     | SAE/GCMP  | Strongest| New       |

WPA2 Personal vs Enterprise:
+------------------------------------------------------------------+

WPA2-Personal (Pre-shared Key):
+------------------------------------------------------------------+
|  - Uses PSK (pre-shared key)                                   |
|  - All users share same password                                |
|  - Suitable for home/small office                              |
|  - Vulnerable to offline dictionary attacks                    |
+------------------------------------------------------------------+

WPA2-Enterprise:
+------------------------------------------------------------------+
|  - Uses RADIUS server + certificates                            |
|  - Individual user credentials                                 |
|  - Suitable for corporate                                      |
|  - More secure                                                 |
+------------------------------------------------------------------+

WPA3 Features:
+------------------------------------------------------------------+
|  - SAE (Simultaneous Authentication of Equals)                 |
|  - 192-bit security suite (Enterprise)                      |
|  - Enhanced protection against offline attacks                |
|  - Easy Connect for IoT devices                               |
+------------------------------------------------------------------+

WiFi Security Best Practices:
+------------------------------------------------------------------+
|  - Use WPA3 or WPA2-AES                                        |
|  - Strong password (12+ characters)                           |
|  - Change default SSID                                         |
|  - Disable WPS                                                 |
|  - Use MAC filtering (not security, but deterrent)           |
|  - Regular firmware updates                                    |
+------------------------------------------------------------------+

+------------------------------------------------------------------+

17.5 WiFi on Linux

NetworkManager

# View WiFi devices
nmcli device wifi list
iw dev

# Scan for networks
nmcli device wifi rescan

# Connect to network
nmcli device wifi connect "SSID" password "PASSWORD"

# Connect to hidden network
nmcli device wifi connect "SSID" password "PASSWORD" hidden yes

# Disconnect
nmcli device disconnect wlan0

# Create hotspot
nmcli device wifi hotspot ifname wlan0 con-name "MyHotspot"

# Show connection details
nmcli connection show
nmcli device show wlan0

iw (Modern Wireless Tool)

# List devices
iw dev
ip link show wlan0

# Scan for networks
iw dev wlan0 scan | grep -E "SSID|signal|freq"

# Get info
iw dev wlan0 link

# Set power management
iw dev wlan0 set power_save off

# Monitor mode (for packet capture)
ip link set wlan0 down
iw dev wlan0 set monitor control
ip link set wlan0 up

wpa_supplicant

# Install
sudo pacman -S wpa_supplicant

# Create config
sudo wpa_passphrase "SSID" "PASSWORD" >> /etc/wpa_supplicant/wpa_supplicant.conf

# Edit /etc/wpa_supplicant/wpa_supplicant.conf
ctrl_interface=/run/wpa_supplicant
update_config=1

network={
    ssid="MyNetwork"
    psk="password"
}

# Connect
sudo wpa_supplicant -B -i wlan0 -c /etc/wpa_supplicant/wpa_supplicant.conf
sudo dhcpcd wlan0

17.6 Wireless Access Point

                    Access Point Modes
+------------------------------------------------------------------+

1. Managed Mode (Infrastructure)
+------------------------------------------------------------------+
|  - Client connects to AP                                        |
|  - Most common mode                                             |
|  - Used for regular WiFi connection                            |
+------------------------------------------------------------------+

2. Master Mode (Access Point)
+------------------------------------------------------------------+
|  - Acts as AP for other devices                                |
|  - Host network                                                 |
|  - Required for creating WiFi network                          |
+------------------------------------------------------------------+

3. Ad-Hoc Mode (IBSS)
+------------------------------------------------------------------+
|  - Device-to-device, no AP                                    |
|  - Mesh networks                                                |
|  - Less common                                                  |
+------------------------------------------------------------------+

4. Monitor Mode
+------------------------------------------------------------------+
|  - For packet capture (aircrack-ng, Wireshark)                |
|  - No connection, just listening                                |
+------------------------------------------------------------------+

Hostapd Configuration:
+------------------------------------------------------------------+

# /etc/hostapd/hostapd.conf
interface=wlan0
driver=nl80211
ssid=MyNetwork
hw_mode=g
channel=6
wpa=2
wpa_passphrase=StrongPassword123
wpa_key_mgmt=WPA-PSK
rsn_pairwise=CCMP

# Enable
sudo systemctl enable hostapd
sudo systemctl start hostapd

+------------------------------------------------------------------+

+------------------------------------------------------------------+

17.7 Wireless Troubleshooting

# Check interface status
ip link show wlan0
ip addr show wlan0

# Check signal
iw dev wlan0 link
nmcli -f SIGNAL,SSID device wifi

# Scan networks
nmcli device wifi rescan
iw dev wlan0 scan | grep SSID

# Check driver
ethtool -i wlan0
lspci -k | grep -A 3 Network

# Check logs
journalctl -u NetworkManager

# Check interference
iw dev wlan0 survey dump

Summary

In this chapter, you learned:

✅ Wireless fundamentals (frequency bands, concepts)
✅ WiFi standards (802.11a/b/g/n/ac/ax)
✅ WiFi channels (2.4 GHz vs 5 GHz)
✅ Wireless security (WEP, WPA, WPA2, WPA3)
✅ WiFi configuration on Linux
✅ Access point modes
✅ Wireless troubleshooting

Next Chapter

Chapter 18: Network Monitoring

Last Updated: February 2026