ProtocolThe rules that govern communications between devices; dictates message encoding, formatting, encapsulation, size, timing, and delivery.
Network Protocol SuiteA group of protocols that work together to define a common format and set of rules for exchanging messages (e.g., TCP/IP).
TCP/IPA protocol suite implemented on both sending and receiving hosts to provide end-to-end delivery of messages; organized into application, transport, internet, and network access layers.
EncapsulationThe process of placing one message format inside another as it moves down the protocol stack.
De-encapsulationThe reverse of encapsulation; removing header/formatting info as data moves up the stack.
Protocol Data Unit (PDU)The form data takes at any given layer of the protocol stack.
SegmentationDividing a message into smaller pieces for transmission.
MultiplexingInterleaving segments from different communications over the same network.
UnicastOne-to-one communication.
MulticastOne-to-many communication.
BroadcastOne-to-all communication.
EthernetA Layer 1/2 protocol (IEEE 802.2/802.3) responsible for data encapsulation and media access control; uses MAC addresses.
MAC AddressA 48-bit physical address (12 hex digits) assigned to a network interface.
IPv6A newer Layer 3 protocol with a 128-bit address space, created to address IPv4 exhaustion.
Subnet MaskUsed to identify the network and host portions of an IPv4 address.
Default GatewayThe router interface that allows a host to reach remote networks.
ICMPInternet Control Message Protocol — used to provide feedback and troubleshoot network problems (e.g., ping, time exceeded, destination unreachable).
PingA utility using ICMP echo request/reply messages to test connectivity.
TracerouteA utility that lists the hops (routers) between source and destination, showing round-trip time (RTT).
ARPAddress Resolution Protocol — resolves IPv4 addresses to MAC addresses; maintains an ARP table (cache).
ARP Spoofing (ARP Poisoning)A security attack where a device falsely replies to ARP requests to intercept traffic meant for another device (e.g., the gateway).
Transport LayerTracks conversations, segments/reassembles data, and identifies applications via port numbers.
TCPTransmission Control Protocol — reliable, connection-oriented transport protocol; acknowledges data and resends lost segments.
UDPUser Datagram Protocol — fast, low-overhead, connectionless transport protocol without reliability guarantees.
SocketThe combination of an IP address and port number that identifies a specific process/connection.
DHCPDynamic Host Configuration Protocol — automatically assigns IP addressing information (IP, subnet mask, gateway, DNS).
DNSDomain Name System — resolves domain names to IP addresses; uses a hierarchical structure (TLDs, second-level domains, subdomains).
FQDNFully Qualified Domain Name — the complete domain name of a specific device in the DNS hierarchy.
Resource Record (RR)A DNS message format containing NAME, TYPE, CLASS, TTL, RDLENGTH, and RDATA fields.
Dynamic DNS (DDNS)Allows automatic updating of DNS records when IP addresses change.
WHOISA TCP-based protocol used to identify domain ownership.
NATNetwork Address Translation — translates private IP addresses to public IP addresses for internet routing.
PATPort Address Translation — a form of NAT that maps many private addresses to one or a few public addresses using different ports.
FTPFile Transfer Protocol — TCP-based protocol for transferring files between hosts.
TFTPTrivial File Transfer Protocol — UDP-based, fast but unreliable file transfer protocol.
SMBServer Message Block — a client/server file-sharing protocol that also manages sessions and printer access.
SMTPSimple Mail Transfer Protocol — sends email between servers/clients (port 25).
POP3Post Office Protocol v3 — downloads and removes email from the server to the client.
IMAPInternet Message Access Protocol — downloads copies of email while keeping them synced with the server.
HTTPHypertext Transfer Protocol — a TCP-based, request/response protocol (port 80) used for web communication; methods include GET, POST, PUT, DELETE, OPTIONS, CONNECT.
LinuxAn open-source operating system created in 1991, maintained by a community of programmers; source files (kernel, shell, applications) are freely available.
Distribution (Distro)A version of Linux defined by its kernel, programs, and software packaging (e.g., CentOS, Fedora, RedHat).
Kali LinuxA Linux distribution that bundles many penetration testing tools.
ShellThe command-line interface (CLI) through which users interact with the Linux OS.
Terminal EmulatorAn application providing access to the CLI (e.g., terminator, xterm, konsole, gnome-terminal).
Root User / SuperuserThe account with absolute administrative control over the Linux system.
sudoRuns another command with superuser privileges.
suSwitches to another user account.
lsLists files inside a directory.
cdChanges the current directory.
mkdirCreates a directory under the current directory.
cpCopies files from source to destination.
mvMoves or renames files and directories.
rmRemoves files.
grepSearches plain-text data for lines matching a regular expression.
catDisplays the contents of a text file.
manDisplays documentation for a specific command.
chmodModifies file permissions.
chownChanges file ownership.
ddCopies data from an input device/file to an output.
pwdDisplays the name/path of the current directory.
psLists the currently running processes.
ifconfigViews or configures network interface settings.
apt-getInstalls software using the advanced package tool.
iwconfigViews or configures wireless network settings.
shutdownLogs off and shuts down the operating system.
passwdChanges a user password.
Text EditorsPrograms used to edit text/configuration files; CLI-based (vi, vim, nano) or GUI-based (gedit).
Configuration FileA text file (often key=value pairs) that defines settings for a service, such as port number or authorized clients.
Client-Server CommunicationA model where servers provide resources/services (files, email, web pages) and clients access them via specific software.
PortA reserved network resource number used to identify a specific service (e.g., 21-FTP, 22-SSH, 80-HTTP, 443-HTTPS).
Log FilesRecords of important system events, including application, event, service, and system logs (e.g., /var/log/messages, /var/log/auth.log, /var/log/secure).
Device HardeningSecurity practices such as disabling unused services, enforcing strong passwords, and keeping systems updated.
ext2Flash-storage optimized file system (no journaling).
ext3Successor to ext2 with journaling.
ext4Successor to ext3 with larger file support and better performance.
NFSNetwork File System — allows file access over a network.
CDFSCompact Disc File System — used for optical media.
Swap File SystemUsed when the system runs out of RAM.
HFS+Apple's Macintosh file system.
APFSApple's updated encrypted file system for flash/SSD storage.
MBRMaster Boot Record — stores partition and file system organization info.
File PermissionsDefined for User, Group, and Other; Read (r), Write (w), Execute (x); expressed in octal (e.g., 7 = rwx).
Hard LinkA file reference pointing to the same data location (inode) as the original file; changes to one affect the other.
Symbolic (Soft) LinkA file that references another file's name/path; breaks if the original is deleted; can span file systems and link to directories.
X Window System (X / X11)The framework underlying the Linux GUI; handles window drawing, mouse/keyboard input, and can serve graphical output remotely.
Window ManagerSoftware (e.g., Gnome, KDE) that defines the look and feel of the desktop GUI.
Package ManagerSoftware that simplifies installing/removing programs and manages dependencies (e.g., APT for Debian, YUM for RedHat, pacman for Arch Linux).
apt-get updateDownloads the latest list of available software from repositories.
apt-get upgradeInstalls updates for all currently installed software.
ProcessA running instance of a program; multiple processes can run simultaneously via multitasking.
ForkingA method allowing a process to create a copy of itself for scalability.
topDynamically lists running processes.
killStops, restarts, or pauses a process.
RootkitMalware installed at the kernel level, often used to create hidden backdoors.
chkrootkitA tool used to detect (and attempt to remove) rootkits on a Linux system.
Piping (|)A technique for chaining commands together, feeding one command's output into another's input.
DaemonA background process/service running on a Linux system.
JournalingA file system feature (used in ext3/ext4) that logs changes before committing them, aiding recovery after a crash.