CompTIA Network+ Domain 1

Physical Layer (Layer 1)

The OSI layer that transmits raw binary bits across physical media using electrical voltages, light pulses, or radio frequencies.

Data Link Layer (Layer 2)

The OSI layer responsible for packaging bits into frames, physical MAC addressing, error detection, and local flow control.

Network Layer (Layer 3)

The OSI layer responsible for logical IP addressing and routing packets across different networks.

Transport Layer (Layer 4)

The OSI layer that manages end-to-end communication, segmentation, error checking, and flow control using TCP or UDP.

Session Layer (Layer 5)

The OSI layer that establishes, maintains, and terminates communication sessions between applications.

Presentation Layer (Layer 6)

The OSI layer that handles data formatting, compression, translation, and encryption or decryption.

Application Layer (Layer 7)

The OSI layer that provides network services directly to end-user software applications.

Layer 1 PDU

Bits

Layer 2 PDU

Frames

Layer 3 PDU

Packets

Layer 4 TCP PDU

Segments

Layer 4 UDP PDU

Datagrams

Layers 5 through 7 PDU

Data

Encapsulation

The process of adding protocol headers and trailers to data as it moves down from Layer 7 to Layer 1.

Decapsulation

The process of removing protocol headers and trailers as data moves up from Layer 1 to Layer 7 at the destination.

Hub

A Layer 1 multiport repeater that broadcasts incoming signals to all ports without logic, creating a single collision domain.

Switch

A Layer 2 network device that forwards frames based on MAC addresses, putting each port in its own collision domain.

Router

A Layer 3 network device that routes packets between different networks based on logical IP addresses and divides broadcast domains.

Multilayer Switch

A switch operating at Layer 2 and Layer 3 that combines fast hardware frame switching with IP routing capabilities.

Firewall

A security appliance that monitors, filters, and controls incoming and outgoing network traffic based on configured security rules.

Intrusion Detection System (IDS)

A passive security device that monitors network traffic and alerts administrators when malicious activity is detected.

Intrusion Prevention System (IPS)

An inline security appliance that actively inspects network traffic and blocks unauthorized or malicious activity in real time.

Load Balancer

A network device that distributes application traffic across multiple backend servers to maximize performance and prevent bottlenecks.

Proxy Server

An intermediary device that processes web requests on behalf of clients to provide caching, web filtering, and anonymity.

Network-Attached Storage (NAS)

A dedicated file-level storage device connected directly to a local area network.

Storage Area Network (SAN)

A specialized, high-speed network that delivers block-level storage access to servers.

Wireless Access Point (WAP)

An infrastructure device that connects wireless client endpoints to a wired local area network via radio signals.

Wireless Controller

A centralized appliance or software solution used to manage, configure, and monitor multiple wireless access points across a network.

Content Delivery Network (CDN)

A globally distributed network of proxy caching servers that delivers web content to users with high availability and low latency.

Virtual Private Network (VPN)

A network service that creates an encrypted logical tunnel across an untrusted network to secure data transmission.

Quality of Service (QoS)

A set of network mechanisms that prioritizes time-sensitive traffic like voice and video to minimize latency and packet loss.

Time to Live (TTL)

An 8-bit IPv4 header field that decrements at each router hop to limit packet lifespan and prevent infinite routing loops.

Network Functions Virtualization (NFV)

The concept of virtualizing dedicated network hardware functions like firewalls and routers as software virtual machines.

Virtual Private Cloud (VPC)

An isolated virtual network environment provisioned within a public cloud provider infrastructure.

Network Security Group (NSG)

A stateful instance-level or vNIC-level cloud firewall rule set used to filter network traffic.

Network Security List

A stateless subnet-level cloud firewall rule set used to control inbound and outbound traffic.

Cloud Internet Gateway

A horizontally scalable VPC component that enables communication between cloud instances and the public internet.

Cloud NAT Gateway

A VPC service that allows instances in private subnets to initiate outbound internet access while blocking inbound internet connections.

Direct Connect / Private Connection

A dedicated, private high-speed WAN connection between an organization's on-premises facility and a cloud provider.

Public Cloud

A multi-tenant cloud deployment model where computing infrastructure is shared across multiple organizations over the public internet.

Private Cloud

A single-tenant cloud deployment model dedicated exclusively to a single organization.

Hybrid Cloud

A cloud deployment model that combines and integrates public and private cloud environments.

Infrastructure as a Service (IaaS)

A cloud service model providing virtualized computing resources like servers, networking, and storage over the internet.

Platform as a Service (PaaS)

A cloud service model providing hardware, operating systems, and developer tools for application building without infrastructure management.

Software as a Service (SaaS)

A cloud service model providing fully managed, web-accessible software applications directly to end users.

Cloud Scalability

The ability of a cloud infrastructure to accommodate long-term workload growth by increasing resource capacity.

Cloud Elasticity

The ability of cloud systems to dynamically expand or contract computing resources in real time based on demand.

Cloud Multitenancy

An architecture where multiple independent customers share the same physical server hardware while keeping their data isolated.

FTP (File Transfer Protocol)

Operates on ports 20 (data) and 21 (control) to transfer files unencrypted over a TCP connection.

SFTP (Secure File Transfer Protocol)

Operates on port 22 using SSH to provide encrypted file transfers.

SSH (Secure Shell)

Operates on port 22 to provide encrypted remote command-line administration and secure data communication.

Telnet

Operates on port 23 to provide unencrypted, plain-text remote command-line access.

SMTP (Simple Mail Transfer Protocol)

Operates on port 25 to send and relay unencrypted email messages between mail servers.

DNS (Domain Name System)

Operates on port 53 using UDP for queries and TCP for zone transfers to translate domain names to IP addresses.

DHCP (Dynamic Host Configuration Protocol)

Operates on port 67 (server) and port 68 (client) to automatically assign IP addresses and network parameters.

TFTP (Trivial File Transfer Protocol)

Operates on port 69 using UDP to provide simple, unencrypted file transfers without authentication.

HTTP (Hypertext Transfer Protocol)

Operates on port 80 to transmit unencrypted web pages across the internet.

NTP (Network Time Protocol)

Operates on port 123 using UDP to synchronize system clocks across network devices.

SNMP (Simple Network Management Protocol)

Operates on port 161 (queries) and port 162 (traps) using UDP to monitor and manage network equipment.

LDAP (Lightweight Directory Access Protocol)

Operates on port 389 to query and manage directory services over plain text.

HTTPS (Hypertext Transfer Protocol Secure)

Operates on port 443 to transmit web traffic securely using SSL/TLS encryption.

SMB (Server Message Block)

Operates on port 445 to provide shared access to files and printers on Microsoft networks.

Syslog

Operates on port 514 using UDP to send system log messages to a central log server.

SMTPS (SMTP Secure)

Operates on ports 465 or 587 to securely transmit email messages using SSL/TLS encryption.

LDAPS (LDAP over SSL)

Operates on port 636 to securely access directory services using SSL/TLS encryption.

MS SQL Server

Operates on port 1433 for Microsoft SQL database connectivity.

RDP (Remote Desktop Protocol)

Operates on port 3389 to deliver graphical remote desktop access to Windows systems.

SIP (Session Initiation Protocol)

Operates on port 5060 (unencrypted) and 5061 (TLS encrypted) to initiate and manage VoIP call sessions.

ICMP (Internet Control Message Protocol)

An IP helper protocol used by diagnostic utilities like ping and traceroute to send operational messages and error reports.

TCP (Transmission Control Protocol)

A connection-oriented, reliable transport layer protocol that guarantees ordered delivery of data via a three-way handshake.

UDP (User Datagram Protocol)

A connectionless, lightweight transport layer protocol that transmits datagrams without establishing a session or guaranteeing delivery.

GRE (Generic Routing Encapsulation)

A tunneling protocol developed by Cisco that encapsulates a wide variety of network layer protocols inside virtual point-to-point links.

IPsec AH (Authentication Header)

An IPsec sub-protocol that provides connectionless data integrity and data origin authentication without encryption.

IPsec ESP (Encapsulating Security Payload)

An IPsec sub-protocol that provides data confidentiality through encryption, along with origin authentication and integrity protection.

IPsec IKE (Internet Key Exchange)

The IPsec protocol responsible for negotiating security associations and exchanging cryptographic keys.

Unicast Traffic

Data transmission sent from a single sender host to a single specific recipient host on a network.

Multicast Traffic

Data transmission sent from one host to a specific designated group of subscribed listening hosts.

Anycast Traffic

Data transmission sent from a sender to the single nearest recipient node among a group of nodes sharing the same address.

Broadcast Traffic

Data transmission sent from one host to every host located within the local broadcast domain.

802.11 Standards

IEEE wireless LAN standard family specifying PHY and MAC layer implementations for Wi-Fi networks.

802.3 Standards

IEEE wired LAN standard family specifying Physical and Data Link specifications for Ethernet networks.

Single-Mode Fiber (SMF)

Optical fiber cable with a narrow core (8-10 microns) that carries laser light in a single path for long-range transmissions without modal dispersion.

Multi-Mode Fiber (MMF)

Optical fiber cable with a wider core (50-62.5 microns) that uses LED light across multiple paths for short-distance network links up to 2 km.

Direct Attach Copper (DAC) / Twinaxial

A high-speed twinax copper cable assembly with factory-terminated transceiver ends used for short-range server rack interconnects.

Coaxial Cable

Shielded copper cable featuring a single central copper conductor surrounded by insulation and metallic braid, used for cable internet and RF.

Plenum-Rated Cable

Fire-retardant cabling jacket designed for air handling spaces that produces low toxic smoke when exposed to heat or flame.

Non-Plenum Cable (PVC)

Standard plastic copper cabling jacket suitable for open office runs that releases toxic fumes if burned.

Ethernet Transceivers

Optical and electrical modular transceivers operating under IEEE 802.3 standards for Ethernet connectivity.

Fibre Channel (FC) Transceivers

Specialized high-speed optical transceivers utilized specifically in Storage Area Networks (SANs) for block storage traffic.

SFP (Small Form-Factor Pluggable)

A compact, hot-swappable optical transceiver module supporting data rates up to 4.25 Gbps.

SFP+ Transceiver

An enhanced SFP form factor supporting network data speeds up to 16 Gbps.

QSFP (Quad Small Form-Factor Pluggable)

A transceiver form factor using four channels to achieve total speeds up to 40 Gbps.

QSFP28 Transceiver

A high-density optical transceiver form factor supporting data rates up to 100 Gbps.

PAN (Personal Area Network)

A short-range network spanning up to 10 feet connecting personal devices via Bluetooth or USB.

LAN (Local Area Network)

A localized network spanning a single room, office, or building, limited to approximately 100 meters per copper cable segment.

CAN (Campus Area Network)

A network connecting multiple local area networks across adjacent buildings within a defined geographical campus.

MAN (Metropolitan Area Network)

A high-speed network spanning a larger geographic area such as a municipality or entire city.

WAN (Wide Area Network)

A network spanning large geographical distances connecting distant branch sites and regions globally.

SAN Topology

A dedicated storage area architecture built specifically to deliver block-level data storage between servers and arrays.

WLAN (Wireless Local Area Network)

A local network that relies on radio frequency waves rather than physical cables to connect endpoint clients.