Network + Chapter 1 OSI Reference Model

Layer 1

Physical

Layer 2

Data link

layer 3

Network

Layer 4

Transport

Layer 5

Session

Layer 6

Presentation

Layer 7

Application

Devices that operate at the physical layer

Hubs, repeaters, and network cables

Hub

A basic networking device that connects multiple computers or other network devices together (layer 1)

Repeaters

Devices that are extend the range of a network by amplifying the signal (layer 1)

The data link layer (layer 2)

Responsible for node-to-node data transfer and error detection and correction

Cyclic Redundancy Check (CRC)

Data and error checking code (layer 2)

Switch

Connects multiple devices within a network and learns MAC addresses to determine the destination of each data frame (layer 2)

Bridges

Connect two or more network segments allowing them to function as a single network. They reduce traffic by dividing the network into segments (layer 2).

MAC Address (Media Access Control)

A hardware address that uniquely identifies each node on a network (Layer 2)

Network Interface Cards (NICs)

Hardware components installed in computers and other network devices providing physical connections to the network and convert data from the device into a format transmittable over the network (Layer 1 + Layer 2)

Network Layer 3

Responsible for routing data between different networks

Router

A device that forwards data packets between different networks by analyzing the destination IP address (Layer 3)

Routing Tables

Contains the information about possible paths helping to determine the most efficient route for data to travel (layer 3)

Layer 3 Switch

Connects devices within the same local network forwarding data based on MAC addresses but also can route data between different parts of the network such as VLANs or subnets

Transport (layer 4)

Handles error correction and data flow control and can provide end-to-end communication.

TCP - Transmission Control Protocol

Connection-oriented network communication providing reliable, ordered, and error-checked delivery of data between applications (layer 4)

Handshake (3 way handshake)

TCP establishing a connection between sender and receiver before any data is transmitted (both sides agree to connection parameters)

UDP - User datagram protocol

Sends datagrams (packets) to the receiver without checking whether they arrive or are in order (used for streaming and gaming because speed is of the essence)

Firewalls

Security devices that monitor and control incoming and outgoing network traffic based on predetermined security rules (layer 4).

Session (Layer 5)

Responsible for establishing, maintaining, and terminating sessions between two communicating devices.

Session

A connection for an ongoing exchange of data between two systems (layer 5).

Checkpointing

Allows the session to resume from a certain point if there is an interruption (layer 5)

Presentation layer (layer 6)

Translates data between the application layer and the lower layers. Responsible for data encryption, decryption, compression, and format translation.

Application layer (layer 7)

The closest layer to the end user. Handles protocols such as HTTP, FTP, and SMTP providing network services directly to applications such as web browsers, email clients, and file transfer programs.

WAFs - Web Application Firewalls

protect web applications by filtering and monitoring HTTP/HTTPs requests blocking web based threats (layer 7).

IPS devices - Intrusion Prevention System

detect and block sophisticated attacks that may exploit vulnerabilities in applications (Mainly operate at layer 7).