Domain 3 Review: IP Connectivity and Routing

Domain 3 is worth 25% of the exam — the single largest domain. It tests routing table interpretation, static routing, OSPF (the primary IGP for CCNA), and first-hop redundancy. If you're short on study time, this domain deserves the most attention. Every question you can answer here is worth more than a question in any other domain.

#Must-Know for Domain 3#link

• ▪Reading routing tables — sources, AD, metric, next-hop
• ▪Longest prefix match — the rule that overrides AD
• ▪Static route configuration — next-hop, exit-interface, or both
• ▪Floating static routes — AD manipulation for backup
• ▪Default route 0.0.0.0/0 and gateway of last resort
• ▪OSPF basics — areas, neighbors, adjacencies, Router ID
• ▪OSPF config — `router ospf 1`, `network`, or `ip ospf` interface method
• ▪OSPF network types — broadcast, P2P, NBMA, point-to-multipoint
• ▪OSPF cost — reference bandwidth and `auto-cost`
• ▪OSPF passive interfaces — best practice for user-facing ports
• ▪OSPF verification — `show ip ospf neighbor`, `show ip route ospf`
• ▪HSRP — active/standby, virtual IP, virtual MAC, priority, preemption
• ▪VRRP — open standard, similar to HSRP
• ▪GLBP — active/active load balancing

#Reading Routing Tables — the Core Skill#link

That output is worth more than any diagram. The codes tell you the source (S, C, L, O, O IA). The `[110/2]` gives AD and metric. The `via X.X.X.X` is the next-hop. The `00:15:42` is the age. Read it in one pass and you know the entire router's worldview.