What is network redundancy and high availability?
Why Interviewers Ask This
Mid-level Networking roles require deep understanding of this topic. Interviewers ask this to separate candidates who truly understand the mechanics from those who only know surface-level concepts.
Answer
Network redundancy eliminates single points of failure by providing backup paths and devices, ensuring the network continues operating if a component fails. Techniques: Link redundancy — multiple physical connections between switches (use STP/RSTP to prevent loops, or LAG/port-channel to aggregate bandwidth). Device redundancy — dual routers/firewalls with failover protocols (HSRP/VRRP for first-hop redundancy — one virtual gateway IP shared by two physical routers). ISP redundancy — connect to multiple ISPs with BGP for failover. Power redundancy — dual PSUs in servers and network equipment, UPS, generator backup. Path redundancy in WAN — primary MPLS with backup Internet VPN. Availability metrics: 99.9% ("three nines") = ~8.7 hours downtime/year; 99.99% ("four nines") = ~52 minutes/year. High availability design must eliminate SPOFs at every tier: access, distribution, core, data center, Internet edge.
Common Mistake
A common mistake is memorizing definitions without understanding implications. When asked this question, go one level deeper — explain what happens when this concept is misused or ignored.