Wireless
Topic 16 of 26. 45 questions: 22 pick one, 5 pick all, 7 type it, 3 put in order, 8 interview
What this topic covers
- 802.11 standards and Wi-Fi generations
- 2.4 vs 5 vs 6 GHz
- non-overlapping channels
- channel width tradeoffs
- CSMA/CA vs CSMA/CD
- SSID BSSID ESS
- autonomous vs controller vs cloud managed APs
- CAPWAP and split MAC
- AP modes
- WPA2 vs WPA3 personal vs enterprise
- 4 way handshake
- roaming 802.11r k v
- RSSI SNR and dBm
- interference and site surveys
- band steering
- guest networks and captive portals
Study it in depth on Octet.
- 1Which IEEE 802.11 amendment is marketed as Wi-Fi 6?
- 2Put these 802.11 amendments in the order they were introduced, oldest first.
- 3Compare the 2.4, 5 and 6 GHz bands. Which would you use for what?
- 4In the US, using 20 MHz channels in the 2.4 GHz band, which set of channels gives neighbouring cells that do not overlap?
- 5How far apart are the center frequencies of neighbouring 2.4 GHz channels, such as channel 1 and channel 2?
- 6A user's Linux laptop reports this. Which 5 GHz channel is it on?
- 7An AP is on 5 GHz channel 100, a DFS channel under both US (FCC) and EU (ETSI) rules, and it detects radar. What must it do?
- 8An office with 40 APs changes every 5 GHz radio from 20 MHz to 80 MHz channels. What usually happens to the total capacity of the building?
- 9Thermal noise grows with channel width. By about how many dB does the noise floor rise when a radio goes from a 20 MHz channel to an 80 MHz channel?
- 10Which statements about Wi-Fi in the 6 GHz band are true? Choose all that apply.
- 11Every AP at the site has its 6 GHz radio enabled and the laptop supports Wi-Fi 6E. A scan from the laptop shows CORP only on 2.4 and 5 GHz. What is the most likely reason?
- 12Why does Wi-Fi use CSMA/CA instead of the CSMA/CD that half-duplex Ethernet used?
- 13Two clients at opposite ends of a long warehouse aisle can both hear the AP but not each other. The AP sees many corrupted frames and retries. Which 802.11 mechanism exists for exactly this problem?
- 14An AP radio transmits at 20 dBm. How many milliwatts is that?
- 15From this output, what is the client's signal-to-noise ratio?
- 16Thirty APs in one building broadcast the SSID CORP and connect to the same wired network, so clients can move between them and keep their IP address. What is the 802.11 name for this whole set?
- 17One AP has a 2.4 GHz radio and a 5 GHz radio and broadcasts three SSIDs on each. How many BSSIDs does it advertise?
- 18Compare autonomous, controller-based and cloud-managed access points. When would you choose each?
- 19A company runs cloud-managed APs with a WPA2-PSK SSID. The vendor's cloud dashboard is down for two hours, but the sites' internet links work. What happens at the sites?
- 20Which UDP port on the controller does the CAPWAP control channel use?
- 21What is CAPWAP, and what does split MAC mean in a controller-based wireless network?
- 22In a Cisco controller design with APs in local mode, which functions does the AP itself perform? Choose all that apply.
- 23APs in VLAN 50 show as registered on the controller at 10.10.10.5 and clients associate in local mode, but no client ever gets an IP address. This ACL is applied inbound on the AP VLAN gateway. What is it blocking?
- 24Put the steps a new Cisco lightweight AP goes through to join a controller in order, first to last.
- 25On a Cisco wireless controller, which AP mode serves no clients and scans all channels full time for rogues, intrusion detection and location?
- 26A Cisco FlexConnect AP at a branch serves a WPA2-PSK WLAN with local switching. The WAN link to the controller fails. What happens to the clients?
- 27What are the differences between WPA2 and WPA3, for both Personal and Enterprise?
- 28Which weakness of WPA2-Personal does WPA3-Personal (SAE) remove?
- 29Which statements about WPA3 are true? Choose all that apply.
- 30On a WPA2-Personal network, a user who knows the passphrase captures another client's traffic over the air. What can they do with it?
- 31Both sides already hold the PMK. Put the messages of the WPA2 4-way handshake in order, first to last.
- 32A client cannot join a WPA2-Personal SSID. A capture of its connection attempt shows this pattern repeating. What is the most likely cause?
- 33A WLAN has protected management frames (802.11w) set to required. Which of these frames is still sent without protection?
- 34A cafe replaces its open guest SSID with OWE (Wi-Fi Enhanced Open). What changes for the guests?
- 35How does Wi-Fi roaming work, and what do 802.11k, 802.11v and 802.11r each add?
- 36Which amendment lets an AP give a client a list of nearby APs and their channels, so the client scans fewer channels before it roams?
- 37Wi-Fi phones on a WPA2-Enterprise SSID go silent for about a second at every roam. Signal is good from two APs everywhere, and the controller trace shows a full EAP exchange with a RADIUS server 40 ms away on each roam. Which change shortens the roams the most?
- 38Barcode scanners near a break room, on 2.4 GHz channel 11, crawl every day from about 11:30 to 13:30 and are fine the rest of the day. A Linux laptop next to them shows this during the slow period. What does the output point to?
- 39Which of these are non-Wi-Fi sources of interference in the 2.4 GHz band? Choose all that apply.
- 40How do you plan and run a wireless site survey for a new office?
- 41How does classic band steering, such as Cisco band select, push dual-band clients toward 5 GHz?
- 42How would you design guest Wi-Fi with a captive portal?
- 43Which of these belong in a typical guest Wi-Fi design? Choose all that apply.
- 44Guests associate to the open guest SSID and get an IP address, but the sign-in page never appears and phones report no internet. The portal server is 10.99.0.10, and before sign-in nothing is permitted except this ACL. What is missing?
- 45How would you design Wi-Fi for a 500-seat lecture hall?