CWDP Roaming and Client Mobility Flashcards

What is 'roam thrashing' and how can a CWDP designer mitigate it?

Answer: Clients rapidly roaming between APs of similar signal strength; mitigated by hysteresis thresholds

Roam thrashing occurs when clients oscillate between APs; RSSI hysteresis thresholds prevent roaming unless a meaningful improvement is detected.

In a Layer 3 roaming scenario, what mechanism preserves a client's IP address when crossing subnet boundaries?

Answer: Mobility tunneling (e.g., GRE tunnel back to anchor AP)

Layer 3 roaming solutions use tunneling (GRE or proprietary) to forward client traffic back through the anchor AP, preserving the original IP.

What is the Pairwise Master Key (PMK) caching mechanism (OKC/PKC) designed to accomplish during roaming?

Answer: Avoid full 802.1X re-authentication by caching session keys

Opportunistic Key Caching (OKC) allows clients to reuse a previously derived PMK with nearby APs, skipping the full EAP exchange.

A hospital deploys VoWi-Fi phones. Nurse stations are 30 meters apart. What AP density consideration ensures seamless voice roaming?

Answer: Cell coverage overlap of 15–20% at -67 dBm or better

Overlapping coverage at -67 dBm ensures VoWi-Fi phones always have a strong candidate AP available before initiating a roam.

Which metric does 802.11k neighbor reports NOT include about neighboring APs?

Answer: Current client count on the neighbor AP

802.11k neighbor reports include BSSID, channel, and regulatory information but do not report the load or client count of neighbors.

What is the key advantage of 802.11r Over-the-DS (Distribution System) fast transition versus Over-the-Air?

Answer: It allows key exchange with the target AP before the client reassociates

Over-the-DS FT pre-stages authentication keys with the target AP via the wired network before the client completes the air-interface roam.