Routing and switching are the twin engines that make internetworking possible. Switching moves frames between devices on the same local network (LAN) using hardware (MAC) addresses; routing moves packets between different networks using logical (IP) addresses. Almost every real network — from a home Wi‑Fi to the global Internet — is built by combining switches (which build LANs) with routers (which glue LANs into an internetwork). For BCS, Bank IT, and IT‑officer exams this topic is a guaranteed source of questions: OSI‑layer mapping, the difference between a hub, switch and router, MAC vs IP forwarding, static vs dynamic routing, distance‑vector vs link‑state, RIP/OSPF/BGP, and small numeric problems on hop counts and address lookups.
Learning objectives
- Distinguish switching (Layer 2) from routing (Layer 3) and know which address each uses.
- Explain how a switch learns MAC addresses, builds a MAC/CAM table, and forwards, floods or filters frames.
- Understand collision domains and broadcast domains and how hubs, switches and routers affect them.
- Describe the three switching techniques: circuit switching, packet switching (datagram & virtual circuit) and message switching.
- Explain how a router forwards a packet using a routing table and longest‑prefix match.
- Compare static vs dynamic routing, and distance‑vector vs link‑state algorithms.
- Know the main protocols: RIP, OSPF, EIGRP, BGP, plus VLAN, STP, ARP, and NAT.
- Solve exam problems: hop‑count/metric selection, routing‑table lookups, and Dijkstra/Bellman‑Ford shortest paths.