The default gateway is the single point of failure nobody notices until it dies. First Hop Redundancy Protocols — HSRP, VRRP, and GLBP — put a virtual IP and virtual MAC in front of two or more routers so that when one fails, the other takes over without a host ever changing its gateway. This is a CCNA 200-301 topic 3.5 deep dive: how a virtual gateway works, the HSRP state machine and its v1/v2 differences, priority and preemption, interface tracking, the open-standard VRRP, Cisco's active-active GLBP, and the IOS configuration and verification commands that make it real.
High-Availability
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CCNA: First Hop Redundancy Protocols — HSRP, VRRP, and GLBP -
PostgreSQL Replication and High Availability PostgreSQL streaming replication setup, synchronous vs asynchronous tradeoffs, logical replication for selective sync and zero-downtime upgrades, pg_basebackup for standby creation, Patroni with etcd for automatic failover, pg_rewind for rejoining a former primary, and monitoring replication lag.
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Redis Architecture and Persistence Redis data structures and their use cases, RDB vs AOF vs hybrid persistence, Redis Sentinel for high availability, Redis Cluster for horizontal scaling with hash slots, eviction policies, diagnostic commands, and an honest look at when Redis is the right tool.
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pfSense and OPNsense: The Complete Home Lab Firewall Guide A comprehensive guide to pfSense and OPNsense — comparing the two platforms, choosing hardware, installing and configuring from scratch, setting up DHCP, DNS-over-TLS, firewall rules, NAT, VLANs, WireGuard, high availability with CARP, packages like pfBlockerNG and Suricata, and hardening your router/firewall for the home lab or small business.