network beginner

peer-to-peer

a decentralized network model where participants interact directly with each other, sharing resources and data without a central server.

Client/Server Network Relationships

a network model where clients request services and resources from centralized servers, which manage and provide the necessary data.

UNDERSTANDING THE OSI NETWORKING MODEL

A conceptual framework used to understand and implement network communications through seven layers, each with specific functions that outline how data is transmitted over a network.

Physical Layer

the topmost layer of the OSI model responsible for enabling end-user services and interactions, such as email and file transfer.

Data-Link Layer

the layer of the OSI model that formats and encodes data for the application layer, ensuring proper data representation between the sender and receiver.

Network Layer

the layer of the OSI model responsible for routing and forwarding data packets between devices across different networks, ensuring data is sent to the correct destination.

Transport Layer

the layer of the OSI model that provides reliable transmission of data segments between points on a network, managing error detection, correction, and flow control.

Session Layer

the layer of the OSI model that establishes, manages, and terminates communication sessions between applications, ensuring proper synchronization and data exchange.

Presentation Layer

the layer of the OSI model that translates, encrypts, and compresses data for the application layer, ensuring that data is presented in a usable format.

Application Layer

the layer of the OSI model that provides network services directly to end-user applications, enabling functions like email, file transfer, and web browsing.

Servers

computers or systems that provide resources, data, services, or programs to other computers, known as clients, over a network.

Hubs, Routers, and Switches

devices used in networking to connect, direct, and manage data traffic between different devices on a network.

Cabling and Cable Plants

Workstation Hardware

refers to the physical components of a workstation, including the computer, monitor, keyboard, and other peripherals designed for tasks such as graphic design, programming, or data analysis.

Bus Topology

one single network cable is used from one end of the network to the other, with different network devices (called nodes) connected to the cable at different locations.

Star Topology

is a network topology where each node is connected to a central hub or switch, allowing for easy management and isolation of devices.

Twisted-Pair Cabling: The King of Network Cables

is a type of cabling used in networking, consisting of pairs of wires twisted together to reduce electromagnetic interference. It is commonly used for telephone and data transmissions.

Hubs and Concentrators

are network devices that connect multiple nodes in a star topology, allowing data to be transmitted between devices. Hubs operate at the physical layer, while concentrators can provide additional functionalities.

Bridges

are networking devices that connect multiple network segments, improving efficiency and reducing collisions by managing data traffic between them.

Routers

are devices that forward data packets between computer networks, directing traffic based on IP addresses. They operate at the network layer of the OSI model.

Switches

are network devices that connect multiple devices within a LAN, using MAC addresses to forward data only to the specific device intended to receive it. They operate at the data link layer of the OSI model.

MAKING HIGH-LEVEL CONNECTIONS WITH GATEWAYS

involves the use of network gateways that facilitate communication between different networks, often translating protocols or data formats to ensure compatibility.

DIRECTING NETWORK TRAFFIC

is the process of managing and controlling the flow of data packets across a network, ensuring efficient communication and resource utilization.

private

A private network is one that is exclusive to a particular company. No other company's data is sent over the private network. The advantages are the data is secure, you can control how the network is used, and you can predict how much bandwidth you have available

Public

. A public network, like the Internet, is a network through which many companies' data passes. Public networks are less secure than private networks, but the advantages are they are less expensive to use and you don't have to maintain the external network yourself.

ADSL

Asymmetric DSL allows for up to 8Mbps of data to be received and up to 1Mbps of data to be sent. Many RBOCs are only offering up to 1.5Mbps to be received (called downstream) and 256Kbps to be sent (called upstream),

HDSL

High-speed DSL allows between 768Kbps and 2.048Mbps connections between two sites.

RADSL

Rate Adaptive DSL allows for 600Kbps to 12Mbps of data to be received and 128Kbps to 1Mbps of data to be sent.

VDSL

Very-high-speed DSL allows up to 51Mbps of data downstream and up to 2Mbps upstream.

xDSL

The twisted-pair copper wire that carries POTS service is capable of carrying signals with up to a 1 MHz spread of frequencies.

• TCP/IP

is a combination of two protocols that work together to manage network communication.

• IP (Internet Protocol)

handles the addressing of data, ensuring it reaches the correct destination and is reassembled properly.

• TCP (Transmission Control Protocol)

adds reliability by checking for errors and ensuring data is received correctly. If packets are lost or damaged, TCP resends them.

• UDP (User Datagram Protocol

is a faster but less reliable alternative to TCP. It doesn’t guarantee all packets arrive or are error-free but is ideal for quick communications like loading web pages.

TCP vs. UDP

TCP is used for important, error-sensitive data (e.g., banking transactions), while UDP is used when speed matters more than accuracy (e.g., streaming or online gaming).

IP Addressing (Internet Protocol)

uniquely identify computers on the internet and help route packets from sender to receiver.

Version

Indicates wheather ip v4 or v6 is in use

Header Lengt

Specifies the length of header info before the actual data

Type of Service

Allows vendors to set priorities (e.g., high reliability or fast routing).

Total Length

Defines the packet’s overall size

Identification, Flags, Fragment Offset

Helps reassemble packets that were split during transmission.

Time to Live (TTL)

Determines the number of network hops a packet can take before being discarded.

Protocol

1. Specifies whether the packet is using TCP or UDP

Header checksum

The header checksum is used to help ensure that none of the packet's header data (the fields being discussed here) is damaged.

Source IP address

This field contains the address of the sending computer. It is needed in case retransmission of a packet is required, in which case the receiving node (or, in some cases, a router) knows from which node retransmission should be requested.

Destination IP address

This field contains the address of the receiving node.

Options and padding

These final two fields of the header of the IP packet are used in case specific routing instructions must be requested or to contain time information of when the packet was sent.

Data

The final field of an IP packet is the actual data being sent.

Domain Name System

Domain names are registered with ICANN and linked to specific computers. When you enter a domain in a web browser, DNS finds the matching IP address, allowing the connection

Dynamic Host Configuration Protocol (DHCP)

A DHCP server manages a range of IP addresses (a "scope"). When a device joins the network, it requests an address from the server.

Leased Addresses

Devices don’t keep their IPs permanently; they use them for a set period before the address is available for reuse.

HTML (Hypertext Markup Language)

The formatting language used to create web pages, including text, images, and links.

Web Browsers

Programs like Microsoft Edge and Chrome display HTML documents.

HTTP (Hypertext Transfer Protocol)

Controls communication between a web client (browser) and a web server, enabling users to access websites.

DNS Integration

HTTP works with DNS to convert domain names (like www.yahoo.com) into IP addresses for seamless connection

Security Concerns

HTTP is insecure since it sends text "in the clear," making data vulnerable. Secure alternatives like HTTPS (SSL/TLS encryption) provide protection.

Connection Behavior

Web connections are not persistent—once a page loads, the connection ends. Clicking links reactivates new connections, either to the same or different servers.

Let me know if you need any additional clarifications!

• FTP (File Transfer Protocol)

enables file transfers between a client and a server over a network.

FTP vs. FTP Program

The protocol (FTP) defines how files are sent, while the program (FTP software) is used to execute those transfers.

Text & Binary Transfers

FTP supports transferring both text and binary files, allowing flexibility for different data types

Authentication

Users typically log in with a username and password, but some servers allow anonymous FTP, where anyone can access files using "anonymous" as the username and an email as the password.

• Telnet Protocol

Enables remote access to an internet-connected host as if the user were physically present at the terminal.

• Functions telnet

users can manage files, run applications, and administer the system remotely (with proper permissions).

Port & Protocol

• Telnet is a TCP-based protocol, typically operating on port 23, but can be configured to use other ports.

Simple Mail Transfer Protocol (SMTP)

Enables email transmission between mail servers, ensuring reliable delivery. The sending system connects to the receiver’s port 25.the sender issues a HELO command with its address; the receiver responds with its own address.The sender specifies the recipient and sends the email body with attachments.

Acknowledgment & Termination SMTP

The receiver confirms receipt, and the connection closes.

Dynamic Addressing

• Unlike TCP/IP, which can require static IPs, IPX dynamically negotiates addresses at login using Ethernet MAC addresses.

• Network Address Structure

• 32-bit network address

• 48-bit node address

• 16-bit connection ID (allows up to 65,000 client/server connections)

Scalability

• The IPX design theoretically supports 281 trillion nodes across 16 million networks.

• LAN to WAN Adaptation

• Originally for LANs, but later enhanced to support WAN connections.

• IPX (Internetwork Packet Exchange)

• is based on Xerox Network Systems (XNS). While it can operate on various network types, it was originally optimized for Ethernet.

Directory Services

Organizes network resources, eliminating chaos in large IT environments.Without directory services, each server would require separate management of users, printers, and configurations, making administration difficult.

• Benefits OF Active directory

• Centralized management – No need to maintain separate user lists on each server.

• Simplified access – Users can query for a resource type (e.g., all printers) and get a complete list.

• Enhanced reliability & security – Distributes services across multiple servers instead of relying on one.

• Tree-Based Organization

• Directory services use a hierarchical structure similar to file directories on a hard disk.

• Root

The top-level entry containing all other objects.

• Containers

Hold other objects, including subcontainers and leaves

• Leaves

• Represent actual network resources like workstations, printers, shared files, or user accounts.

• Attributes (Properties)

Each object has specific attributes that define its characteristics:

• Printer object

Stores details like name, administrator, and location.

• User account object

Includes name, password, and access permissions.

• Variability Across Systems

Different directory services use similar attribute structures but vary in implementation.

Remote acces needs

Easy remote access to e-mail and files stored in e-mail • Remote access to stored private or shared files on the LAN • Remote access to a centralized application, like an accounting system or a sales order system • Remote access to groupware programs or custom applications • Remote access to any of the previous from a fixed location, such as a remote sales office .A. Remote access to any of the previous from anywhere in the world

Firewall

A system that enforces a security policy between two networks, such as between a LAN and the Internet. Firewalls can use many different techniques to enforce security policies.

Proxy server

A server that acts as a proxy, usually for users of a network. For example, it may stand in as a proxy for browsing Web pages, so that the user's computer isn't connected to the remote system, except through the proxy server.

Packet filter

Usually built into a router, a packet filter enables you to set criteria for allowed and disallowed packets, source and destination IP addresses, and IP ports.

Internal security

Internal security focuses on protecting a network from insider threats, which account for more than 75% of security incidents.

Unauthorized Access

Employees viewing payroll, accounting, or other sensitive data.

User Impersonation

Sending emails under someone else's identity to cause disruption.

• File Access Violations

Accessing or modifying files without proper authorization.

• Criminal Activities

Using internal systems for fraud, data theft, or embezzlement.

File and Directory Permissions

• Best practices include role-based access control (RBAC), structured permissions, audits, and least privilege principles.Setting permissions at top-level directories simplifies management.

• Logging, encryption, and automation strengthen security.

Create only

a type of role enables users to add a new file to a directory, but they cannot see, edit, or delete existing files, including any they've created.

Read only

This role enables users to see the files in a directory and they can even pull up the files for viewing on their computer. However, they cannot edit or change the stored files in any way.

Change

This role lets users do whatever they like with the files in a directory, except they cannot give other users access to the directory.

Full control

Usually reserved for the "owner" of a directory, this role enables the person(s) to do whatever they like with the files in a directory and, further, they have the ability to grant other users access to the directory

EXTERNAL SECURITY

the process of securing the network from external threats.

Front-door threats

This is where someone, from outside the company, somehow finds, guesses, or cracks a user password and then logs on to the network.

Back-door threats

threats where software or hardware bugs in the network's OS and hardware enable an outsider to crack the network's security. Once accomplished, the outsider often finds a way to log in to the administrative account, and then can do anything he or she likes .

Denial of service

These are attacks that deny service to the network. Examples include specific actions that are known to crash different types of servers or flooding the company's Internet connection with useless traffic (such as a flood of PING requests).

Viruses

A computer virus is a program that spreads by infecting other files with a copy of itself. Files that can be infected by viruses include program files (.COM, .EXE, and .DLL) and document files