Most people picture a router as the box between the LAN and the internet. Inside a real company network, routing does far more — connecting subnets, bounding broadcast domains, enforcing security zones, linking sites, and surviving failures. A tour of why internal routing exists.
Routing
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Routers Inside the Enterprise: What They Do Besides Reach the Internet -
CCNA: EIGRP Fundamentals EIGRP from first principles: DUAL algorithm, successor and feasible successor selection, the feasibility condition, composite metric calculation, unequal-cost load balancing, neighbor tables, topology tables, and complete Cisco IOS configuration and verification.
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CCNA: IPv4 Routing Fundamentals How routers make forwarding decisions, the routing table in depth, administrative distance, static routes with next-hop vs exit-interface, default routes, recursive lookups, and connected/local routes — with full Cisco IOS CLI examples.
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CCNA: OSPF Single-Area Configuration OSPF from first principles through production configuration: link-state database, DR/BDR election, the seven neighbor states, Hello/Dead timers, LSA types, passive interfaces, cost tuning, and complete Cisco IOS CLI examples.
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FRRouting in Production: The Linux Router That Replaces Cisco for Many Use Cases FRRouting turns commodity Linux into a serious router — the stack behind Cumulus, SONiC, and Cilium's BGP mode. How to run BGP and OSPF in production, and where FRR is a genuine alternative to Cisco and Juniper.
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OSPF for DevOps Engineers: Link-State Routing Without the CCNA OSPF link-state routing explained for DevOps engineers, not CCNA candidates — enough theory to run multiple routers with FRR in a homelab or datacenter, understand areas and LSAs, and debug why a route isn't where you expect.