Which of the following descriptions of BFD characteristics are correct? (Multiple choice)

Question

Options

• AThe detection mechanism of BFD includes detection mode, detection time and detection
• BThe BFD protocol stipulates that the unit of sending interval and receiving interval is
• CThe BFD detection mechanism is that two systems establish a BFD session and periodically send
• DBFD control packets are encapsulated in TCP packets and transmitted

• A
  74% (32)
• D
  26% (11)

Explanation

A, B, and C correctly describe BFD (Bidirectional Forwarding Detection) behavior. BFD's detection mechanism is built on three pillars: the detection mode (asynchronous or demand), the detection time (calculated as the negotiated interval × detection multiplier), and the multiplier itself - making A accurate. B is correct because BFD specifies interval values in microseconds, enabling sub-second failure detection. C accurately captures BFD's core operation: two peers negotiate and establish a session, then periodically exchange control packets; if packets stop arriving within the detection time, the link is declared failed.

D is wrong because BFD control packets are encapsulated in UDP (port 3784 for single-hop, 4784 for multi-hop), not TCP. TCP's connection-oriented overhead would defeat BFD's purpose of ultra-fast, lightweight fault detection.

Memory tip: Think "BFD = Blazing Fast Detection" - it uses UDP (connectionless, fast) not TCP (slow handshakes), and its timers are in microseconds not milliseconds. If an answer says TCP or milliseconds for BFD intervals, it's a trap.

No community discussion yet for this question.