Physical Layer

Handles the transmission of raw bits over physical media like cables and wireless signals. Deals with voltage levels

Data Link Layer

Provides node-to-node data transfer and handles error detection/correction. Uses MAC addresses and is where switches operate. Includes LLC and MAC sublayers

Network Layer

Responsible for logical addressing and routing packets between different networks. This is where routers operate and IP addresses are used

Transport Layer

Ensures reliable data transfer between hosts with error checking and flow control. Handles segmentation and can provide connection-oriented or connectionless communication

Session Layer

The Session Layer (Layer 5) of the OSI model is responsible for establishing, managing, and terminating dialogues (sessions) between applications on different devices.

Presentation Layer

Translates data between application and network formats. Handles encryption

Application Layer

Closest to end users and provides network services directly to applications. Where protocols like HTTP

TCP/IP Application Layer

Combines OSI layers 5-7. Provides network services and protocols that applications use to communicate

TCP/IP Transport Layer

Provides end-to-end communication services. Uses TCP for reliable

TCP/IP Internet Layer

Handles logical addressing and routing of packets across networks. IP protocol operates here along with ICMP and ARP

TCP/IP Network Access Layer

Combines OSI layers 1-2. Handles physical transmission of data and local network protocols like Ethernet and WiFi

Class A IP Range

1.0.0.0 to 126.0.0.0 with default mask 255.0.0.0. First bit is 0

Class B IP Range

128.0.0.0 to 191.255.0.0 with default mask 255.255.0.0. First two bits are 10

Class C IP Range

192.0.0.0 to 223.255.255.0 with default mask 255.255.255.0. First three bits are 110

Private IP Ranges

10.0.0.0/8

Subnet Mask

Binary pattern that determines which portion of an IP address represents the network and which represents the host

CIDR Notation

Shorthand method using a slash followed by the number of network bits. Example: 192.168.1.0/24 means first 24 bits are network

Default Gateway

Router IP address that devices use to send traffic destined for other networks. Acts as the exit point from the local network

IPv6

128-bit addressing system using hexadecimal notation separated by colons. Designed to replace IPv4 due to address exhaustion

TCP

Connection-oriented protocol that guarantees delivery with error checking

UDP

Connectionless protocol that sends data without establishing a connection or guaranteeing delivery. Faster but less reliable

HTTP

Port 80 protocol for transferring web pages and resources. Uses request-response model between clients and servers

HTTPS

Port 443 protocol that adds encryption to HTTP using SSL/TLS. Secures data transmission between client and server

DNS

Port 53 service that translates domain names into IP addresses. Operates hierarchically with root

DHCP

Port 67/68 protocol that automatically assigns IP addresses and network configuration to devices on a network

ARP

Protocol that maps IP addresses to MAC addresses on a local network. Maintains a cache of recent mappings

ICMP

Protocol used for diagnostic and error-reporting purposes. Powers tools like ping and traceroute

FTP

Port 21 protocol for transferring files between systems. Sends credentials and data in cleartext

SFTP

Port 22 protocol that provides secure file transfer over SSH with encryption. Not related to FTPS

SSH

Port 22 protocol providing secure remote access and command execution. Uses encryption and supports key-based authentication

Router

Operates at Layer 3 and forwards packets between different networks based on IP addresses. Makes routing decisions

Switch

Operates at Layer 2 and forwards frames within a network based on MAC addresses. Creates separate collision domains

Hub

Operates at Layer 1 and broadcasts all traffic to every connected device. Creates one large collision domain

Firewall

Security device that monitors and filters traffic based on predetermined rules. Can operate at multiple layers

Access Point

Device that allows wireless devices to connect to a wired network. Broadcasts SSIDs and manages wireless connections

Modem

Device that modulates and demodulates signals to connect a local network to an ISP. Converts between analog and digital

Load Balancer

Distributes network traffic across multiple servers to optimize resource use and prevent overload

MAC Address

48-bit physical address burned into network interface hardware. Consists of 6 hexadecimal octets separated by colons or hyphens

Port Numbers

16-bit numbers that identify specific processes or services on a host. Range from 0-65535 with well-known ports below 1024

Common Ports

HTTP:80

Broadcast

Transmission sent to all devices on a network segment. Uses MAC address FF:FF:FF:FF:FF:FF or IP ending in .255

Unicast

One-to-one transmission sent from one source to one specific destination. Most common traffic type

Multicast

One-to-many transmission sent to a group of interested recipients. Uses special IP address range 224.0.0.0 to 239.255.255.255

Collision Domain

Network segment where data packets can collide. Switches create separate collision domains for each port

Broadcast Domain

Network segment where broadcast traffic is propagated. Routers separate broadcast domains while switches don't

NAT

Technique that translates private IP addresses to public ones for internet communication. Conserves public IP addresses

VLAN

Logical segmentation of a network at Layer 2 that creates separate broadcast domains on the same physical switch

VPN

Encrypted tunnel that allows secure communication over public networks. Creates a virtual private connection

Bandwidth

Maximum data transfer rate of a network connection. Measured in bits per second

Throughput

Actual data transfer rate achieved in practice. Usually lower than bandwidth due to overhead and congestion

Latency

Time delay for data to travel from source to destination. Measured in milliseconds and affects responsiveness

Half-Duplex

Communication mode where data flows in both directions but only one direction at a time. Example: walkie-talkies

Full-Duplex

Communication mode where data flows in both directions simultaneously. Modern switches and NICs use this

Packet Structure

Data unit consisting of header (source/destination info

Three-Way Handshake

TCP connection establishment process using SYN

command - ipconfig

Displays IP configuration information

command - ping

Tests Connections to other IP ports

command - netstat

Displays network connections.

command - tracert

Displays the route taken to the destination

command - nslookup

Directly queries the name server for information on a destination domain.