High Availability
Designing networks with redundancy so services stay online despite component failures.
High availability (HA) is an architecture strategy that eliminates single points of failure so critical network services stay accessible despite hardware faults, software crashes, or maintenance windows. Common implementations include redundant power supplies, dual uplinks, NIC teaming, and clustering, where a standby node takes over automatically if the active node fails. The exam distinguishes HA from disaster recovery: HA prevents downtime through real-time redundancy, while disaster recovery restores operations after a major outage using backups and alternate sites. Uptime is expressed as a percentage — “five nines” (99.999%) allows roughly five minutes of downtime per year.
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