Overview
802.11 Wi-Fi is Layer 2 wireless Ethernet. At CCNA depth, focus on RF behavior, channels, service sets, and how wireless differs from switched Ethernet — not every PHY amendment detail.
Wireless Fundamentals (Day 55)
Video credit: Jeremy's IT Lab
Watch on YouTubeWhy wireless is different
| Wired Ethernet | Wi-Fi |
|---|---|
| Dedicated cable to each device | Shared air — all stations in range hear frames |
| CSMA/CD collision detection | CSMA/CA collision avoidance |
| Contained inside the building | Signal leaks through walls — privacy matters more |
Devices wait for the medium to be idle before transmitting. Hidden-node problems motivate RTS/CTS awareness at CCNA level.
RF behavior (exam awareness)
Signals weaken and distort through the environment:
| Effect | CCNA takeaway |
|---|---|
| Absorption | Energy lost passing through materials (walls) → weaker SNR |
| Reflection | Bounces off metal — poor reception in elevators |
| Refraction | Bends entering new medium (glass, water) |
| Diffraction | Bends around obstacles — blind spots behind them |
| Scattering | Dust/smoke/rough surfaces spread energy |
Higher frequency (5 GHz) generally means higher throughput but shorter range and poorer penetration than 2.4 GHz.
Frequency bands and channels
| Band | Range (approx.) | CCNA note |
|---|---|---|
| 2.4 GHz | 2.400–2.4835 GHz | Only 1, 6, 11 non-overlapping in North America |
| 5 GHz | 5.150–5.825 GHz | Many non-overlapping channels — easier planning |
| 6 GHz (Wi-Fi 6E) | Awareness only | Extended spectrum in 802.11ax |
Channel 3 overlaps both 1 and 6. Adjacent APs on overlapping 2.4 GHz channels cause co-channel interference.
Plan AP placement in a honeycomb using channels 1, 6, 11 so neighboring cells do not overlap. ESS coverage areas (BSAs) should overlap about 10–15% for smooth roaming.
Service sets
All devices in a service set share the same SSID (human-readable name). Each AP radio has a unique BSSID (AP MAC).
| Type | Name | Behavior |
|---|---|---|
| IBSS | Independent / ad hoc | Clients connect directly — no AP; not scalable |
| BSS | Basic | Clients associate through one AP |
| ESS | Extended | Multiple APs, same SSID, different BSSIDs/channels, wired DS |
| MBSS | Mesh | MAPs backhaul wirelessly to a root AP (RAP) |
Wireless LAN components — AP, WLC, distribution system, and clients.
Supplementary figure from Panagiss CCNAmd
Distribution system and VLAN mapping
The distribution system (DS) is the wired network behind the WLAN. Each WLAN/SSID maps to a VLAN on the wired side. An AP can advertise multiple SSIDs (unique BSSIDs) over a trunk to the switch.
Specialty AP roles (awareness)
| Mode | Use |
|---|---|
| Repeater | Extends BSS range — single-radio repeaters halve throughput |
| Workgroup bridge (WGB) | Connects wired devices without Wi-Fi to a remote AP |
| Outdoor bridge | Point-to-point or point-to-multipoint long-distance link |
802.11 standards (awareness)
Know that 802.11n/ac/ax improve throughput and efficiency. CCNA tests concepts (bands, channels, association, security) more than memorizing every data rate table.
Exam checklist
- Name 2.4 GHz non-overlapping channels: 1, 6, 11
- Explain CSMA/CA vs CSMA/CD
- Define SSID, BSSID, BSS, ESS, IBSS, DS, BSA
- Compare 2.4 vs 5 GHz tradeoffs
- Describe honeycomb channel planning and ESS roaming overlap