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IP SLA & BFD: Active Path Monitoring

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Active monitoring: detecting failures before routing protocols do

Routing protocols (OSPF, BGP) detect neighbor failures through hello timers — typically 40 seconds for OSPF dead timers. A link degradation (high packet loss, latency spike) that doesn't bring down the interface may never be detected at all. Traffic blackholes for minutes.

IP SLA (Service Level Agreement) and BFD (Bidirectional Forwarding Detection) take an active approach: continuously probe paths and trigger actions when quality degrades. IP SLA is application-aware (can simulate VoIP, HTTP, DNS), while BFD is protocol-integrated and ultra-fast (sub-second detection).

Packets in motion — click to inspect:

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