2.1 Routing Fundamentals: Static Routing, Administrative Distance & Dynamic IGPs
Examines route selection mechanics, Administrative Distance priority, link-state vs. distance-vector protocols, and autonomous system routing.
Key CompTIA Network+ Exam Takeaways
- Administrative Distance ranks route trustworthiness: Connected (0) > Static (1) > eBGP (20) > OSPF (110) > RIP (120).
- OSPF is a link-state IGP using the Dijkstra SPF algorithm, requiring all non-backbone areas to connect to Area 0.
- BGP is the Path Vector protocol powering inter-Autonomous System routing across the Internet.
Routers maintain a Routing Information Base (RIB) to forward packets. When multiple routing sources learn paths to the identical destination prefix, the router selects the path with the lowest Administrative Distance (AD).
Open Shortest Path First (OSPF) establishes neighbor relationships via Hello packets and exchanges Link State Advertisements (LSAs). OSPF constructs a complete topology database and computes loop-free shortest paths using the Dijkstra algorithm.
Border Gateway Protocol (BGP) operates at the Internet scale, exchanging path vectors and autonomous system numbers (ASNs) to enforce global routing policies.
A core enterprise router learns two competing routes to the remote destination subnet 10.50.0.0/16 with identical prefix lengths: one route is learned dynamically via OSPF, and the second route is configured as a static route without an explicit administrative distance parameter. Which route will the router install into its active routing table?