Table of Contents

A

Access Control List (ACL): Rules that permit or deny network traffic based on source/destination IP, port, or protocol. Used in firewalls and routers for security.

Access Point (AP): Wireless network device that allows WiFi-enabled devices to connect to a wired network.

Active Directory (AD): Microsoft's directory service for Windows domain networks, providing centralized authentication and management.

Address Resolution Protocol (ARP): Protocol that maps IP addresses to MAC (hardware) addresses on a local network.

Administrative Distance (AD): Trustworthiness rating of routing protocol sources (0-255, lower is better). Static routes = 1, OSPF = 110, RIP = 120.

Anycast: Routing method where multiple servers share same IP address; client connects to nearest/best one. Used by DNS root servers, CDNs.

Application Layer: Layer 7 of the OSI model; handles protocols like HTTP, FTP, SMTP, DNS directly used by applications.

ARP Spoofing: Attack where attacker sends fake ARP messages to link their MAC address to another host's IP address, enabling man-in-the-middle attacks.

Autonomous System (AS): Collection of IP networks under single administrative control, using unified routing policy. Identified by AS Number (ASN).

Availability: Network reliability measurement; percentage of time systems are operational. "Five nines" (99.999%) = ~5 minutes downtime per year.

B

Backbone: High-capacity network connections that carry bulk of traffic between different network segments or regions.

Bandwidth: Maximum rate of data transfer across a network path, measured in bits per second (bps, Mbps, Gbps).

BGP (Border Gateway Protocol): Path-vector routing protocol used to exchange routing information between autonomous systems on the internet.

Bit: Smallest unit of data in computing (0 or 1). 8 bits = 1 byte.

Broadcast: Transmission sent to all devices on a network segment (destination: 255.255.255.255 or FF:FF:FF:FF:FF:FF).

Broadcast Domain: Network segment where broadcast packets can reach. Routers separate broadcast domains; switches don't.

Byte: 8 bits of data. Common measurement for file sizes and data transfer.

C

Cable Categories: Standards for twisted-pair Ethernet cables:

  • Cat5e: Up to 1 Gbps, 100 meters
  • Cat6: Up to 10 Gbps (55m), 100 meters for 1 Gbps
  • Cat6a: Up to 10 Gbps, 100 meters
  • Cat7/Cat8: Data center use, shorter distances, higher speeds

Carrier Sense Multiple Access with Collision Detection (CSMA/CD): Ethernet method where devices listen before transmitting and detect collisions. Obsolete with modern switches.

CIDR (Classless Inter-Domain Routing): IP addressing method using variable-length subnet masks (e.g., 192.168.1.0/24 instead of Class C).

Client: Device or software that requests services from a server.

Collision Domain: Network segment where collisions can occur. Switches create separate collision domain for each port; hubs don't.

Core Layer: Top tier of three-tier network architecture; high-speed backbone providing fast transport between distribution layer devices.

CRC (Cyclic Redundancy Check): Error-detection code used in Ethernet frames to detect transmission errors.

D

Data Link Layer: Layer 2 of OSI model; handles MAC addresses, frames, and physical transmission between adjacent nodes (switches operate here).

Default Gateway: Router IP address that devices use to send traffic to destinations outside their local subnet.

DHCP (Dynamic Host Configuration Protocol): Automatically assigns IP addresses and network configuration to devices. See DHCP Guide.

DHCP Lease: Time period that IP address is assigned to device before requiring renewal (typically 8-24 hours).

DHCP Relay: Forwards DHCP broadcasts from clients to DHCP servers on different subnets (also called IP Helper).

DHCP Scope: Range of IP addresses available for DHCP assignment to clients.

DMZ (Demilitarized Zone): Network segment isolated from both internal network and internet, hosting public-facing servers.

DNS (Domain Name System): Translates domain names (google.com) to IP addresses (142.250.80.46). See DNS Guide.

DORA: DHCP process - Discover, Offer, Request, Acknowledge.

DoS (Denial of Service): Attack that makes network resource unavailable by overwhelming it with traffic.

DDoS (Distributed Denial of Service): DoS attack from multiple sources simultaneously, harder to mitigate.

Duplex: Communication mode:

  • Simplex: One-way only (TV broadcast)
  • Half-Duplex: Two-way but not simultaneous (walkie-talkie)
  • Full-Duplex: Simultaneous two-way (telephone, modern Ethernet)

E

EAP (Extensible Authentication Protocol): Authentication framework used in wireless networks (WPA2/WPA3-Enterprise) and point-to-point connections.

EIGRP (Enhanced Interior Gateway Routing Protocol): Cisco's advanced distance-vector routing protocol with fast convergence.

Encapsulation: Process of wrapping data with protocol headers at each OSI layer as it traverses the network stack.

Encryption: Converting data into coded format to prevent unauthorized access. Common types: AES, 3DES, RSA.

Ethernet: Most common LAN technology standard (IEEE 802.3), using twisted-pair or fiber cables with CSMA/CD.

EtherType: Field in Ethernet frame identifying which protocol is encapsulated (e.g., 0x0800 = IPv4, 0x86DD = IPv6).

F

Failover: Automatic switching to redundant system when primary fails, ensuring continuous availability.

Fiber Optic: Cable using light pulses through glass/plastic fibers for high-speed, long-distance transmission. Types: single-mode (long), multi-mode (short).

Firewall: Security device that filters network traffic based on rules, blocking unauthorized access. See Firewall Guide.

Frame: Data unit at Layer 2 (Data Link), containing MAC addresses, payload, and error checking (CRC).

FTP (File Transfer Protocol): Protocol for transferring files between computers (port 21 control, 20 data).

FQDN (Fully Qualified Domain Name): Complete domain name including host and domain (<www.example.com>).

G

Gateway: Device that connects two different networks, often with different protocols (commonly refers to default gateway/router).

Gbps (Gigabits per second): Data transfer rate of 1 billion bits per second.

Gigabit Ethernet: Ethernet standard supporting 1 Gbps (1000BASE-T for copper, 1000BASE-X for fiber).

GRE (Generic Routing Encapsulation): Tunneling protocol that encapsulates network layer protocols inside IP tunnels.

H

Handshake: Process of establishing connection and negotiating parameters (e.g., TCP three-way handshake: SYN, SYN-ACK, ACK).

Hop: Each router or Layer 3 device a packet passes through between source and destination.

Hop Count: Number of routers packet must traverse; used as metric by RIP.

Host: Any device with IP address on network (computer, server, printer, phone, etc.).

HTTP (HyperText Transfer Protocol): Protocol for web page transfer (port 80).

HTTPS (HTTP Secure): Encrypted version of HTTP using TLS/SSL (port 443).

Hub: Legacy network device that broadcasts data to all connected ports (single collision domain). Replaced by switches.

I

ICMP (Internet Control Message Protocol): Protocol for diagnostic and error messages (used by ping and traceroute).

IDS (Intrusion Detection System): Monitors network traffic for suspicious activity and alerts administrators.

IEEE (Institute of Electrical and Electronics Engineers): Organization that develops networking standards (802.3 Ethernet, 802.11 WiFi).

IGP (Interior Gateway Protocol): Routing protocol used within autonomous system (OSPF, EIGRP, RIP, IS-IS).

Internet: Global network of interconnected computer networks using TCP/IP protocols.

Intranet: Private network using internet protocols, accessible only within organization.

IoT (Internet of Things): Network-connected devices (smart home, sensors, cameras, appliances).

IP (Internet Protocol): Network layer protocol for addressing and routing packets (IPv4, IPv6).

IP Address: Numerical identifier assigned to device on IP network (e.g., 192.168.1.100 for IPv4, 2001:db8::1 for IPv6).

IPsec (Internet Protocol Security): Protocol suite for securing IP communications through authentication and encryption, commonly used in VPNs.

IPv4: Internet Protocol version 4, using 32-bit addresses (e.g., 192.168.1.1), supporting ~4.3 billion addresses.

IPv6: Internet Protocol version 6, using 128-bit addresses (e.g., 2001:0db8:85a3::8a2e:0370:7334), supporting 340 undecillion addresses.

ISP (Internet Service Provider): Company providing internet access to customers.

J

Jitter: Variation in packet arrival times, critical for real-time applications like VoIP and video conferencing.

Jumbo Frames: Ethernet frames larger than standard 1500-byte MTU (typically 9000 bytes), used in data centers for efficiency.

K

Kerberos: Network authentication protocol using secret-key cryptography, used in Active Directory and enterprise systems.

Kilo (K): Prefix meaning 1,000 (in networking, 1 Kbps = 1,000 bits per second).

L

LAN (Local Area Network): Network within limited area (home, office, building), typically high-speed with low latency.

Latency: Time delay between data transmission and reception, measured in milliseconds (ms).

Layer 2 Switch: Operates at Data Link layer, forwarding frames based on MAC addresses.

Layer 3 Switch: Can perform routing functions in addition to switching, using IP addresses.

LDAP (Lightweight Directory Access Protocol): Protocol for accessing and maintaining directory services (commonly used with Active Directory).

Lease: Duration that DHCP assigns IP address to client before renewal required.

Link Aggregation: Combining multiple network connections into single logical link for increased bandwidth and redundancy (also called bonding, teaming, LAG).

Load Balancer: Device distributing network traffic across multiple servers to optimize resource use and reliability.

Localhost: Loopback address referring to local computer (127.0.0.1 for IPv4, ::1 for IPv6).

Loopback: Virtual interface on device that always refers back to itself, used for testing.

M

MAC Address (Media Access Control): Unique 48-bit hardware identifier assigned to network interface (e.g., aa:bb:cc:dd:ee:ff). First 24 bits identify manufacturer.

MAC Table: Switch database mapping MAC addresses to physical ports.

MAN (Metropolitan Area Network): Network covering city or metropolitan area, larger than LAN but smaller than WAN.

Mbps (Megabits per second): Data transfer rate of 1 million bits per second.

MDI/MDI-X: Ethernet wiring configurations. Modern equipment auto-detects, eliminating need for crossover cables.

Metric: Value used by routing protocols to determine best path (hop count, bandwidth, delay, etc.).

MIMO (Multiple Input Multiple Output): Wireless technology using multiple antennas to improve performance.

Modem: Device that modulates/demodulates signals for transmission over cable, DSL, or fiber lines to ISP.

MTU (Maximum Transmission Unit): Largest packet size that can be transmitted without fragmentation (typically 1500 bytes for Ethernet).

Multicast: Transmission from one sender to specific group of receivers (destination: 224.0.0.0 - 239.255.255.255).

Multiplexing: Combining multiple signals into one for transmission over single medium.

MX Record: DNS Mail Exchange record specifying mail servers for domain.

N

NAT (Network Address Translation): Translates private IP addresses to public IP for internet access, conserving public IPs.

NetBIOS: Legacy Microsoft protocol for LAN name resolution and file sharing (gradually replaced by DNS/SMB).

Network: Collection of interconnected devices able to communicate and share resources.

Network Layer: Layer 3 of OSI model; handles IP addressing and routing (routers operate here).

Next-Hop: IP address of next router in path to destination.

NIC (Network Interface Card): Hardware component that connects computer to network, has unique MAC address.

NTP (Network Time Protocol): Protocol for synchronizing system clocks over network (port 123 UDP).

O

OFDM (Orthogonal Frequency-Division Multiplexing): Modulation technique used in WiFi for efficient spectrum use.

OSI Model (Open Systems Interconnection): Seven-layer conceptual framework for understanding network communications. See OSI Model Guide.

OSPF (Open Shortest Path First): Link-state IGP routing protocol, widely used in enterprise networks. See Routing Guide.

OUI (Organizationally Unique Identifier): First 24 bits of MAC address identifying manufacturer.

P

Packet: Data unit at Layer 3 (Network), containing source/destination IP addresses and payload.

PAT (Port Address Translation): Type of NAT mapping multiple private IPs to single public IP using different ports.

PDU (Protocol Data Unit): Data unit at specific layer (Frame at L2, Packet at L3, Segment at L4, Data at L7).

Physical Layer: Layer 1 of OSI model; handles electrical signals, cables, connectors (hubs, repeaters, cables operate here).

Ping: Diagnostic tool using ICMP to test connectivity and measure round-trip time.

PoE (Power over Ethernet): Technology delivering electrical power over Ethernet cables (standards: 802.3af = 15.4W, 802.3at = 25.5W, 802.3bt = 51-73W).

Port: Logical endpoint for network communication. Physical port: connector on device. Logical port: number identifying service (HTTP=80, HTTPS=443, SSH=22).

Port Forwarding: NAT feature redirecting traffic from external port to internal IP/port, allowing internet access to internal servers.

Port Security: Switch feature limiting devices on port by MAC address, preventing unauthorized connections.

Presentation Layer: Layer 6 of OSI model; handles data formatting, encryption, compression.

Private IP Addresses: Reserved address ranges for local networks (not routable on internet):

  • 10.0.0.0/8 (10.0.0.0 - 10.255.255.255)
  • 172.16.0.0/12 (172.16.0.0 - 172.31.255.255)
  • 192.168.0.0/16 (192.168.0.0 - 192.168.255.255)

Protocol: Set of rules governing network communication (TCP, UDP, IP, HTTP, etc.).

Proxy: Intermediary server between clients and destination servers, used for caching, filtering, anonymity.

Public IP Address: Globally unique IP address routable on the internet (assigned by ISPs, obtained from IANA).

Q

QoS (Quality of Service): Prioritizing certain traffic types (voice, video) over others (downloads, backups) for consistent performance.

Queue: Buffer holding packets awaiting transmission or processing.

R

RADIUS (Remote Authentication Dial-In User Service): Protocol for centralized authentication, authorization, and accounting. Used in WPA2/WPA3-Enterprise.

RARP (Reverse Address Resolution Protocol): Maps MAC address to IP address (reverse of ARP). Largely obsolete (replaced by DHCP).

RDP (Remote Desktop Protocol): Microsoft protocol for remote graphical access to Windows systems (port 3389).

Redundancy: Having backup systems/paths to maintain service during failures.

RIP (Routing Information Protocol): Distance-vector IGP using hop count as metric (max 15 hops). Legacy protocol. See Routing Guide.

RJ45: Standard 8-pin modular connector used for Ethernet cables.

Roaming: Wireless client transitioning between access points while maintaining connection.

Rogue Access Point: Unauthorized wireless AP on network, creating security vulnerability.

Round-Robin: Load balancing method distributing requests sequentially across servers.

Route Summarization: Combining multiple routes into single advertisement to reduce routing table size.

Router: Layer 3 device that forwards packets between different networks using IP addresses.

Routing: Process of selecting paths for network traffic from source to destination across networks.

Routing Protocol: Protocol that automatically discovers routes and builds routing tables (OSPF, EIGRP, BGP, RIP).

Routing Table: Database in router listing networks, next-hops, and metrics for forwarding decisions.

RSSI (Received Signal Strength Indicator): Measurement of wireless signal strength (typically -30 to -90 dBm).

RTT (Round-Trip Time): Time for packet to travel from source to destination and back, measured by ping.

S

Segment: Data unit at Layer 4 (Transport); TCP segment or UDP datagram.

Server: Computer or software providing services to clients (web server, file server, DHCP server).

Session Layer: Layer 5 of OSI model; manages sessions/connections between applications.

SFTP (SSH File Transfer Protocol): Secure file transfer protocol using SSH encryption (port 22).

SIEM (Security Information and Event Management): Centralized logging and analysis platform for security monitoring.

SMTP (Simple Mail Transfer Protocol): Protocol for sending email (port 25, 587).

SNMP (Simple Network Management Protocol): Protocol for monitoring and managing network devices (port 161 for queries, 162 for traps).

Socket: Combination of IP address and port number (e.g., 192.168.1.10:80).

Spanning Tree Protocol (STP): Prevents loops in switched networks by blocking redundant paths (IEEE 802.1D).

SSID (Service Set Identifier): WiFi network name broadcast by access points.

SSH (Secure Shell): Encrypted protocol for remote command-line access (port 22), replacing insecure Telnet.

SSL (Secure Sockets Layer): Deprecated encryption protocol (replaced by TLS). Term still commonly used.

Subnet: Division of larger IP network into smaller logical networks.

Subnet Mask: 32-bit number defining which portion of IP address is network vs. host (e.g., 255.255.255.0 or /24).

Subnetting: Dividing network into smaller subnetworks for better management and efficiency.

Switch: Layer 2 device that forwards frames based on MAC addresses, creating separate collision domain per port.

SYN Flood: DoS attack exploiting TCP handshake by sending many SYN packets without completing connection.

T

TCP (Transmission Control Protocol): Connection-oriented, reliable Layer 4 protocol ensuring ordered delivery (used by HTTP, FTP, SSH).

TCP/IP: Suite of protocols forming foundation of internet (TCP, IP, UDP, ICMP, etc.).

Telnet: Insecure protocol for remote command-line access (port 23). Replaced by SSH.

TFTP (Trivial File Transfer Protocol): Simple file transfer protocol without authentication (port 69 UDP), used for network device firmware.

Three-Way Handshake: TCP connection establishment process (SYN → SYN-ACK → ACK).

Throughput: Actual data transfer rate achieved (lower than bandwidth due to overhead).

TLS (Transport Layer Security): Cryptographic protocol for secure communication over networks, successor to SSL (HTTPS uses TLS).

Topology: Physical or logical layout of network devices and connections (star, mesh, ring, bus).

Traceroute: Diagnostic tool showing path packets take through network (traceroute on Linux/Mac, tracert on Windows).

Transport Layer: Layer 4 of OSI model; handles end-to-end communication (TCP, UDP).

Trunk: Switch port carrying traffic for multiple VLANs using 802.1Q tagging.

TTL (Time To Live): Field in IP packet limiting lifetime (decremented at each hop, packet dropped at 0). Also: DNS record caching duration.

U

UDP (User Datagram Protocol): Connectionless, unreliable Layer 4 protocol for speed over reliability (used by DNS, DHCP, streaming).

Unicast: Transmission from one sender to one specific receiver (most common traffic type).

Uplink: Connection from lower-level device to higher-level (switch to router, branch to HQ, local to internet).

URL (Uniform Resource Locator): Web address (e.g., https://www.example.com/page).

UTM (Unified Threat Management): All-in-one security appliance combining firewall, VPN, IDS/IPS, antivirus, content filtering.

V

Virtual IP (VIP): IP address not tied to specific physical device, used for load balancing or high availability (VRRP, HSRP).

VLAN (Virtual Local Area Network): Logical network segmentation within physical network, separating broadcast domains. See VLAN Guide.

VLAN Tagging: Adding 802.1Q header to Ethernet frames to identify VLAN membership.

VoIP (Voice over IP): Technology for voice calls over IP networks instead of traditional phone lines.

VPN (Virtual Private Network): Encrypted tunnel over internet allowing secure remote access to private network.

VRRP (Virtual Router Redundancy Protocol): Protocol providing automatic gateway failover for high availability.

W

WAN (Wide Area Network): Network spanning large geographic area, connecting multiple LANs (typically slower than LAN).

WAP (Wireless Access Point): See Access Point.

WEP (Wired Equivalent Privacy): Obsolete WiFi security protocol, easily broken. Never use.

WiFi: Wireless networking technology based on IEEE 802.11 standards. See Wireless Guide.

WiFi 6 (802.11ax): Latest WiFi standard offering improved speed, capacity, and efficiency.

WINS (Windows Internet Name Service): Legacy Microsoft service for NetBIOS name resolution (replaced by DNS).

Wireshark: Popular open-source packet analyzer for network troubleshooting and analysis.

WLAN (Wireless Local Area Network): Wireless network using WiFi technology.

WPA (WiFi Protected Access): Wireless security protocol, replaced WEP. Versions: WPA, WPA2, WPA3 (current standard).

WPA2: WiFi security standard using AES encryption, minimum acceptable security for wireless networks.

WPA3: Latest WiFi security standard with improved encryption and protection against brute-force attacks.

X

x.509: Standard format for public key certificates used in TLS/SSL and other security protocols.

Y

Yottabyte (YB): 1,000,000,000,000,000,000,000,000 bytes (1 septillion bytes). Largest data unit.

Z

Zero-Day: Security vulnerability unknown to vendor, with no patch available.

Zero Trust: Security model assuming no implicit trust, requiring verification for every access request.

Zeroconf (Zero Configuration Networking): Technologies enabling automatic network configuration without manual setup or DHCP (includes Bonjour, mDNS).

Zone File: DNS configuration file containing resource records for domain.

Zone Transfer: Replication of DNS zone data from primary to secondary nameserver.

Contributing

This glossary is continuously updated. For corrections or additions, please refer to the documentation contribution guidelines.

This glossary provides quick reference for networking terminology. For detailed explanations, see the linked comprehensive guides.

Edit this page