Computer Networks Notes for Placements and Interviews

Read in this order

1. Introduction to Computer Networks — Computer networks from the ground up: LAN, MAN and WAN, network topologies, hubs, switches and routers, circuit vs packet switching, and delays worked out.
2. The OSI Model — The seven OSI layers from application to physical: each layer's job, PDU, protocols and devices, encapsulation step by step, and a mnemonic for the order.
3. The TCP/IP Model — The TCP/IP model's four layers and the protocols at each, how they map onto the seven OSI layers, and the OSI vs TCP/IP differences interviewers ask about.
4. IP Addressing and Subnetting — IPv4 addresses, classes A to E, private ranges, CIDR and subnet masks, fully worked subnetting and VLSM examples, supernetting, and IPv4 vs IPv6 compared.
5. TCP and UDP — TCP and UDP at the transport layer: ports, header fields, the three-way handshake and four-way close, sliding windows, congestion control, and TCP vs UDP.
6. Domain Name System (DNS) — How DNS turns names into IP addresses: the root, TLD and authoritative hierarchy, recursive and iterative lookups step by step, record types, caching and TTL.
7. HTTP and HTTPS — How HTTP works: requests and responses, methods, status codes, headers, cookies and sessions, HTTP/1.1 vs HTTP/2 vs HTTP/3, and how HTTPS adds TLS on top.
8. Routing and Routing Protocols — How routers choose paths: routing tables, longest prefix match, static vs dynamic routing, distance vector and link state worked out, and RIP vs OSPF vs BGP.
9. Data Link Layer: Framing, Error Control and MAC — The data link layer explained: framing and bit stuffing, parity, checksum and a worked CRC, Hamming code, Go-Back-N and Selective Repeat, ARP and CSMA/CD.
10. NAT, DHCP and Ports — Well-known port numbers, sockets, how NAT and PAT translate private addresses with a worked translation table, DHCP's DORA process step by step, and APIPA.
11. What Happens When You Type a URL — The classic networking interview question answered end to end: URL parsing, caches, DNS, ARP, TCP and TLS handshakes, the HTTP request and page rendering.
12. Network Security Basics — Network security basics: the CIA triad, symmetric vs asymmetric encryption, hashing, digital signatures and certificates, firewalls, VPNs and common attacks.

Test yourself

• Computer Networks · Basic proctored skill test with a verifiable credential
• Computer Networks · Intermediate proctored skill test with a verifiable credential

Other subjects

• Operating Systems
• Database Management Systems
• Object-Oriented Programming