Routing Concepts

Routing Concepts — IP Connectivity (25%) Routing concepts form the backbone of the largest exam domain (25%), meaning a strong grasp of how routers make forwarding decisions, read their routing tables, and use administrative distance will directly protect your score on both simulation and multiple-choice questions. --- ## What Is Routing? Routing is the process by which a router determines the best path to forward a packet toward its destination. Unlike switches, which operate at Layer 2 using MAC addresses, routers operate at Layer 3 using IP addresses. Every time a packet arrives on a router interface, the router must answer one question: *Where do I send this next?* --- ## The Routing Table The routing table (also called the RIB — Routing Information Base) is the router's map of known networks. You view it with: `` show ip route ` ### Route Codes Each entry in the routing table is tagged with a code indicating how the router learned about it: | Code | Meaning | |------|---------| | C | Connected — directly attached network | | L | Local — the router's own interface IP (/32) | | S | Static — manually configured by an admin | | O | OSPF — learned via OSPFv2 | | * | Candidate default route | When you see C 192.168.1.0/24 and L 192.168.1.1/32 together, the C entry represents the whole subnet; the L` entry is that specific interface address — the router uses this to identify traffic destined *for itself*. --- ## Administrative Distance (AD) When a router learns about the *same destination* from multiple sources, it uses Administrative Distance to pick the most trustworthy source. Lower AD…