H12-311_V3.0 · Question #370
In order to solve the tunnel aggregation problem of WLAN roaming, which of the following statements is correct for the processing principles of downlink broadcast and multicast packets? (Multiple…
The correct answer is A. At the HAC, discard unknown unicast packets at the entrance of the roaming tunnel C. The transparently transmitted broadcast/multicast packets reach the FAC, and the FAC converts. In WLAN tunnel aggregation roaming, the HAC (Home Access Controller) and FAC (Foreign Access Controller) divide responsibilities to prevent unnecessary traffic from flooding the roaming tunnel. Option A is correct because unknown unicast packets at the HAC should be dropped at…
Question
In order to solve the tunnel aggregation problem of WLAN roaming, which of the following statements is correct for the processing principles of downlink broadcast and multicast packets? (Multiple choice)
Options
- AAt the HAC, discard unknown unicast packets at the entrance of the roaming tunnel
- BAt the HAC, discard the multicast or broadcast packets of ARP, ND, DHCP, and mDNS to avoid
- CThe transparently transmitted broadcast/multicast packets reach the FAC, and the FAC converts
- DFAP discards unknown unicast packets, and then forwards other packets to roaming STAs
How the community answered
(28 responses)- A79% (22)
- B14% (4)
- D7% (2)
Explanation
In WLAN tunnel aggregation roaming, the HAC (Home Access Controller) and FAC (Foreign Access Controller) divide responsibilities to prevent unnecessary traffic from flooding the roaming tunnel. Option A is correct because unknown unicast packets at the HAC should be dropped at the roaming tunnel entrance - since no destination is confirmed, flooding them through the tunnel wastes bandwidth and creates instability. Option C is correct because broadcast/multicast packets that are legitimately transmitted transparently through the tunnel do reach the FAC, which then converts or processes them (e.g., converting broadcast to unicast) before delivering to the roaming STA.
Option B is wrong because ARP, ND, DHCP, and mDNS broadcasts are essential for address resolution, IP assignment, and service discovery - silently discarding them at the HAC would break fundamental network operations for the roaming client. Option D is wrong because it misassigns the responsibility: it is the HAC (not the FAP) that discards unknown unicast packets at the tunnel entrance; the FAP's role is downstream delivery, not tunnel-entrance filtering.
Memory tip: Use the mnemonic "HAC Kills Unknowns, FAC Converts Broadcasts" - HAC acts as the gatekeeper (dropping unknown unicast before they pollute the tunnel), while FAC acts as the translator (receiving and converting legitimate broadcast/multicast for the roaming STA).
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