AWS Direct Connect VIFs default to BGP timers of 90 seconds hold timer and 30 seconds keepalive (1/3 of hold). This means without BFD, BGP detects dead sessions in roughly 90 seconds. For sub-second detection, BFD is configured with 300 ms hello interval and multiplier 3 (~900 ms detect). Without BFD, three consecutive missed keepalives (every 30s) trigger session reset; BFD complements this with much faster detection.

白話文解釋

DX's default BGP heartbeat is 30 seconds; it gives up after 90 seconds of silence. To get faster failure detection, layer BFD on top with millisecond-scale heartbeats.

選項分析

A：Correct. AWS DX default BGP timers are 90s hold, 30s keepalive.
B：180/60 are RFC defaults; AWS DX commonly negotiates 90/30.
C：30/10 are aggressive; not the AWS default.
D：Long timers do not meet DX SLA targets.