Routing tables, default gateway, longest-prefix match

Routers do not ask 'which route seems generally closest?' They compare the destination IP against candidate prefixes and choose the most specific matching route, called longest-prefix match. The selected route then determines the next hop or outgoing interface.

StackShade deck

Predict → explain → retrieve

COURSE CONTENTS

01How the Internet Works + OSI ModelWeek 1 · 4 topics0/4

OSI Model Explained — interactive deep dive15 min OSI Layer Explorer + Encapsulation Simulator15 min What happens when you type google.com12 min TCP handshake + OSI vs TCP/IP + practice quiz15 min

02Physical & Data Link LayersWeek 1–2 · 5 topics0/5

Signals, bandwidth, latency, copper vs fiber vs radio12 min Ethernet frames, MAC addresses, ARP in action14 min Interactive: ARP resolution walkthrough10 min Switches, VLANs, and why hubs died12 min Trace a frame across 2 switches (worksheet)20 min

03Network Layer: IP & RoutingWeek 2–3 · 6 topics0/6

IPv4 anatomy: network vs host bits, CIDR15 min Interactive: subnet calculator playground15 min Routing tables, default gateway, longest-prefix match12 min NAT, private ranges, and why IPv6 exists12 min How routers learn: static, RIP, OSPF, BGP (bird's-eye)14 min Subnet 3 networks + design a small topology30 min

04Transport Layer: TCP & UDPWeek 3–4 · 5 topics0/5

TCP deep dive: handshake, sequence numbers, ACKs, retransmission16 min Animated 3-way handshake + teardown10 min Flow control (rwnd) vs congestion control (cwnd, slow start)14 min UDP & QUIC: why HTTP/3 ditched TCP12 min Analyze a TCP stream in a packet capture25 min

05Application Layer: HTTP, DNS & FriendsWeek 4–5 · 6 topics0/6

DNS end-to-end: resolver → root → TLD → authoritative14 min Interactive: DNS lookup journey10 min HTTP/1.1 vs 2 vs 3: multiplexing, streams, QUIC14 min TLS handshake, certificates & the chain of trust14 min WebSockets, SMTP/IMAP, DHCP essentials12 min Inspect real requests in browser DevTools20 min

06Security & Troubleshooting ToolkitWeek 5 · 5 topics0/5

Firewalls, VPNs, proxies: what each one really filters12 min Common attacks: SYN flood, DNS spoofing, MITM (defense view)14 min Interactive: layer-by-layer troubleshooting scenarios15 min Hands-on: ping, traceroute, dig, curl, netstat30 min Wireshark: follow one full HTTP conversation30 min