89 Essential Computer Network Concepts You Need to Master

Basic Network Elements

Host

: Any device that can connect to a network (e.g., smartphone, tablet, PC, server, IoT device). Communication link: Physical medium that connects nodes (coaxial cable, twisted‑pair, fiber, wireless). Transmission rate: Speed of data transfer on a link, expressed in bit/s (bps). Packet: Unit of data that includes a header and payload; packets are forwarded across the network. Router: Network‑layer device that forwards packets based on a forwarding table. Path: Sequence of links and switches a packet traverses from source to destination. ISP: Internet Service Provider that supplies connectivity (e.g., mobile carriers, telecom operators). Network protocol: Set of rules governing data exchange between communicating entities. IP: Internet Protocol defining packet format for host‑to‑host communication. TCP/IP protocol suite: Core protocols (TCP, IP, ICMP, ARP, UDP, DNS, SMTP, etc.) that enable Internet communication. Distributed application: Software that runs on multiple hosts and exchanges data. Socket interface: API that provides end‑to‑end communication primitives (e.g., BSD sockets). Protocol: Formal specification of message formats and ordering. Client / Server: Roles in a client‑server architecture; the client initiates requests, the server fulfills them. Forwarding table: Mapping inside a router that determines the outgoing interface for a given destination. Delay: Total time for a packet to travel across the network (transmission, propagation, processing, queuing). Packet loss: Event where one or more packets fail to reach the destination. Throughput: Amount of successfully delivered data per unit time. Message, Segment, Datagram, Frame: Terminology for application‑layer, transport‑layer, network‑layer, and link‑layer units respectively.

Addressing and Naming

IP address

: Unique identifier for a host; can be public or private (IPv4 32‑bit, IPv6 128‑bit). Port number: Numerical identifier on a host that distinguishes concurrent application processes. URI / URL: Uniform Resource Identifier / Locator used to name and locate resources on the Internet. HTML: HyperText Markup Language, the standard language for creating web pages. Web page: Collection of resources (HTML, images, scripts, etc.) addressed by a URL. Web server: Software (e.g., Apache, Nginx, IIS) that serves web pages to clients. CDN: Content Delivery Network that caches content at edge locations to reduce latency. WAF: Web Application Firewall that filters HTTP/HTTPS traffic according to security policies. WebService: Platform‑independent remote invocation mechanism (e.g., SOAP, REST). HTTP: Application‑layer protocol for transferring hypertext data. Session: Server‑side state object (often stored in memory, e.g., ConcurrentHashMap) that maintains client context across multiple HTTP requests. Cookie: Small data item set by a server and returned by the browser to maintain session state. SMTP: Simple Mail Transfer Protocol for sending email over TCP. DNS: Domain Name System that maps human‑readable names to IP addresses. Telnet / SSH: Remote login protocols; SSH provides encrypted communication. FTP: File Transfer Protocol for transferring files between client and server.

Transport‑Layer Mechanisms

MIME type

: Internet media type that describes the format of a payload (e.g., text/html, image/png). Demultiplexing: Receiver process that uses source/destination ports to deliver data to the correct socket. Multiplexing: Sender process that combines data from multiple sockets into packets. Well‑known ports: Port numbers 0‑1023 reserved for standard services. Connection‑oriented: Communication that requires a handshake before data exchange. Three‑way handshake: TCP connection establishment (SYN, SYN‑ACK, ACK). MSS: Maximum Segment Size – largest payload a TCP segment can carry. MTU: Maximum Transmission Unit – largest payload a link can transmit. Redundant ACK: Duplicate ACK indicating possible packet loss. Fast retransmit: Immediate retransmission of a lost segment before its timer expires. Selective acknowledgment (SACK): Allows TCP to acknowledge non‑contiguous data blocks. Congestion control: Algorithms (e.g., slow start, AIMD) that reduce sending rate when network congestion is detected. Four‑way handshake: TCP connection termination (FIN, ACK, FIN, ACK).

Routing and Forwarding

Routing algorithm

: Determines the path packets take through the network (e.g., distance‑vector, link‑state). Forwarding: Action of moving a packet from an input link to the appropriate output link. Packet scheduling: Determines the order of packet transmission on an output link (FIFO, priority queuing, weighted fair queuing). IPv4 / IPv6: Internet Protocol versions; IPv4 uses 32‑bit addresses, IPv6 uses 128‑bit addresses. Interface: Boundary between a host and a physical link. ARP: Resolves IPv4 addresses to MAC addresses on a local network. RARP: Reverse ARP, obtains an IP address from a known MAC address. Proxy ARP: Allows ARP requests to be answered across subnet boundaries. ICMP: Internet Control Message Protocol for error reporting and diagnostics (e.g., ping). DHCP: Dynamic Host Configuration Protocol that automatically assigns IP configuration. NAT: Network Address Translation that maps private addresses to public ones. IP tunnel: Encapsulation of IP packets within another protocol to traverse incompatible networks. Unicast, Broadcast, Multicast, Anycast: Communication scopes ranging from one‑to‑one to one‑to‑many. IGP / EGP: Interior vs. Exterior Gateway Protocols for routing within or between autonomous systems. RIP, OSPF, MPLS: Specific routing protocols and technologies.

Link‑Layer and Physical Layer

Node

: Device operating at the link layer (e.g., host, switch). Link: Physical channel connecting adjacent nodes. MAC protocol: Media Access Control rules governing frame transmission on a shared medium. Parity bit / Forward error correction: Simple error‑detection and correction techniques. Ethernet: Dominant LAN technology defining wiring, signaling, and MAC behavior. VLAN: Virtual LAN that groups ports logically regardless of physical location. Base station: Wireless infrastructure element that provides radio access.