You now understand how to design networks that survive failures.
You learned to calculate availability percentages and how redundancy levels (N+, N, N+) trade cost for resilience. You can identify single points of failure in any topology.
You configured FHRPs: HSRP and VRRP for active/standby gateway redundancy, GLBP for active/active load balancing. You understand link aggregation, dual-homing, and NIC teaming.
You know how failover detection works, how BFD provides millisecond convergence, and how to test failover before disaster strikes. You can prevent split brain and perform maintenance without downtime.