Network Fundamentals

Chapter 1 Introduction to Networking

After completing this module, you should be able to:

1. Distinguish between peer-to-peer and client-server networks.
2. Identify types of applications and protocols used on a network.
3. Describe various networking hardware devices and the most common physical topologies.
4. Describe the seven layers of the OSI model.
5. Explain best practices for safety when working with networks and computers.
6. Describe the seven-step troubleshooting model for troubleshooting network problems.

Network Troubleshooting Scenario

A technician found a workstation with no network connection in a new building during the verification phase. All other workstations on the floor were connected. The technician followed these steps:

1. Checked the patch panel and network switch number.
2. Rechecked physical connections for the PC.
3. Verified network settings in the PC's operating system.
4. Checked the VLAN setting on the switch.
5. Tried a known working port on the switch.
6. Tried different cables.
7. Used a wire toner to trace the cable.

The problem was a wrongly routed cable, which was found in a downstairs closet. After connecting the cable to a switch in the closet, the PC was able to verify a proper network connection. The technician labeled the cable in the patch panel and at the wall for future identification.

Defining a Network

A network consists of computers and other devices (e.g., printers) connected by some type of transmission media. Networks can vary greatly in size and complexity, from a small home office network to the Internet.

Networks can link various devices, including smartphones, personal computers, mainframe computers, printers, corporate phone systems, security cameras, vehicles, and wearable technology devices. They can communicate through copper wires, fiber-optic cable, or radio waves.

Network Models: Physical vs. Logical Topology

Topologies

A topology describes how the parts of a whole work together.

• Physical topology: Refers to a network’s hardware and how computers, devices, cables, or radio signals work together to form the physical network.
• Logical topology: Refers to how software controls access to network resources, including how users and software initially gain access to the network, and how specific resources such as applications and databases are shared on the network.

Network Operating Systems (NOS)

Controlling how users and programs access network resources is managed by the operating systems. The OS is configured to use either the peer-to-peer model or the client-server model.

• Peer-to-peer model: Can be achieved using various desktop, mobile, or tablet OSs.
• Client-server model: Requires a NOS (network operating system), which controls access to the entire network. Examples include Windows Server 2019, Ubuntu Server, and Red Hat Enterprise Linux.

Examples of server operating systems are Windows Server 2019, Ubuntu Server, and Red Hat Enterprise Linux. Network devices like routers and switches also require a NOS, often called networking software, managed through a CLI (command-line interface). Examples include IOS (Internetwork OS) on Cisco devices and Junos OS on Juniper devices. Hypervisors and cloud platforms can also be considered a type of NOS.

The connecting lines in diagrams describe the logical arrangement or topology of computers, as opposed to the physical arrangement.

Peer-to-Peer (P2P) Network Model

In a P2P network, each computer's operating system controls access to its resources without centralized control. Computers, called nodes or hosts, form a logical group sharing resources.

Each computer on a P2P network controls its own administration, resources, and security. Examples of operating systems suitable for peer-to-peer networks are Windows, Linux, macOS, or Chrome OS on desktop and laptop computers, and iOS, Android, or Chrome OS on mobile devices.

Devices in a P2P network can share resources through file sharing or user accounts. Most OSs offer options for sharing files with peered devices, even those running different OSs.

When all computers in a peer-to-peer network are running a Windows OS, resources can be shared using Windows folder and file sharing or a Windows workgroup. Each computer maintains a list of users and their rights. Combining folder and file sharing with workgroups can be confusing, so it’s best to stick with one method.

Generally, a peer-to-peer network is suitable for fewer than about 15 computers.

Advantages of Peer-to-Peer Networks:

• Simple to configure, suitable for environments with limited time or technical expertise.
• Less expensive to set up and maintain than other types of networks.

Disadvantages of Peer-to-Peer Networks:

• Not scalable: Adding or changing significant elements of the network may be difficult as the network grows larger.
• Not necessarily secure: Data and other resources shared by network users can be easily discovered and used by unauthorized people in simple installations.
• Not practical for connecting more than a few computers: Managing resources on the network becomes too time-consuming.

Setting up a file server using P2P file sharing requires creating user accounts and matching passwords on both the server and workstations, which can be difficult to manage. For managing many users and shared resources, it’s best to implement Windows Server or another NOS.

Client-Server Network Model

In the client-server network model, resources are managed by the NOS via a centralized directory database. The database can be managed by one or more servers with a similar NOS installed.

When Windows Server controls network access to a group of computers, this logical group is called a Windows domain. The centralized directory database containing user account information and security for the entire group of computers is called Active Directory (AD).

Each user has a domain-level account in Active Directory, assigned by the network administrator. This account can be a local account (specific to that domain) or a Microsoft account (linking local domain resources with Microsoft cloud resources). Users can sign on to the network from any computer and access resources allowed by Active Directory.

This process is managed by AD DS (Active Directory Domain Services). A computer making a request from another is called the client.

Clients on a client-server network can run applications installed on the desktop and store their own data on local storage devices. Clients don’t share their resources directly; access is controlled by entries in the centralized domain database.

The NOS (e.g., Windows Server 2019, Ubuntu Server, or Red Hat Enterprise Linux) is responsible for:

• Managing data and other resources for clients.
• Ensuring that only authorized users access the network.
• Controlling which types of files a user can open and read.
• Restricting when and from where users can access the network.
• Dictating which rules computers will use to communicate.
• Supplying applications and data files to clients in some situations.

Servers that have a NOS installed require more memory, processing power, and storage capacity than clients because servers must handle heavy processing loads and requests from multiple clients. Servers might use a RAID (redundant array of independent disks) configuration of hard drives for redundancy.

Advantages of Client-Server Networks over Peer-to-Peer Networks:

• User accounts and passwords are assigned in one place.
• Access to multiple shared resources can be centrally granted to a single user or groups of users.
• Problems can be monitored, diagnosed, and often fixed from one location.
• Client-server networks are more scalable.

Client-Server Applications

The resources a network makes available to its users include applications and the data provided by these applications, collectively referred to as network services.

Client-server applications involve at least two endpoint devices, such as computers or smartphones. The client computer requests data or a service from the server. The computers do not need to reside on the same network.

To handle a request, the client computer must find the web server, agree on communication protocols, and then make the request. The server sends its response in the form of a web page.

Communication relies on protocols, which are methods and rules for communication. The primary network protocols are TCP (Transmission Control Protocol) and IP (Internet Protocol), and the suite of protocols an OS uses is the TCP/IP suite.

Popular Client-Server Applications and Their Protocols:

• Web service: Uses HTTP (Hypertext Transfer Protocol) for web servers and browsers. HTTPS (HTTP Secure) is HTTP layered on top of SSL (Secure Sockets Layer) or TLS (Transport Layer Security) for secure transmission.
  • Popular web server applications: Apache and Nginx (free and open source, primarily run on Linux systems), and IIS (Internet Information Services) embedded in Windows Server.
• Email services: Uses SMTP (Simple Mail Transfer Protocol) to send email from the client to the SMTP server. The receiver's mail server delivers the message to the receiving client using POP3 (Post Office Protocol, version 3) or IMAP4 (Internet Message Access Protocol, version 4). Both these protocols are available over SSL or TLS for security.
  • POP3 downloads email to the client computer and typically removes it from the server.
  • IMAP4 manages email while it remains stored on the server.
  • Example email server application: Microsoft Exchange Server. Example email client application: Outlook.
• DNS service: DNS (Domain Name System) helps clients find web servers over a network. Companies and Internet providers run DNS servers.
• FTP service: FTP (File Transfer Protocol) transfers files between two computers. FTP does not provide encryption and is, therefore, not secure.
  • SFTP(Secure File Transfer Protocol) is an encrypted and secure file transfer protocol, which is based on the SSH protocol.
  • Web browsers can work as FTP clients, but dedicated FTP client applications offer more features.
  • Examples: FileZilla and CuteFTP.
• Database services: Databases store massive amounts of data organized into tables and records. A DBMS (database management system) is software installed on the database server responsible for making requested changes to the data and organizing the data for viewing, reporting, or exporting.
  • Many DBMSs use SQL (Structured Query Language) to configure and interact with the database.
  • Examples of SQL database software: Microsoft SQL Server, Oracle Database, and MySQL (open-source).
• Remote access service: Allows an administrator or user to access a remote computer to control it remotely.
  • Telnet is a command-line application, but transmissions are not encrypted.
  • SSH (Secure Shell) protocol creates an encrypted channel between two computers.
  • In Windows operating systems, RDP (Remote Desktop Protocol) provides secure, encrypted transmissions.

Network Hardware

A network requires each node to have a network address. Applications and data are the payload, operating systems are the traffic controllers, and hardware is the road system on which the traffic flows.

LANs and Their Hardware

LANs (local area networks) have nodes that can communicate directly with each other, usually within a small space (e.g., office or building). Devices connect to a switch via wired connections.

A switch receives incoming data from one of its ports and redirects (or switches) it to another port or multiple ports that will send the data to its intended destination(s) within the local network. The physical topology used by this network is called a star topology because all devices connect to the central device, the switch. In a physical topology of the net work, each device can connect to multiple other devices, which is called a mesh topology.

Legacy Networking: Hubs

A hub is an inefficient and outdated networking device replaced by switches. A hub accepted signals from a transmitting device and repeated those signals to all other connected devices in a broadcast fashion. On Ethernet networks, hubs once served as the central connection point for a star topology.

Traffic is greatly reduced with switches because, when a switch receives a transmission from a device, the switch sends it only to the destination device or devices rather than broadcasting to all devices connected to the switch.

Network Ports and NICs

Computers, network printers, switches, and other network devices have network ports into which you plug a network cable. A network port can be an onboard network port embedded in the computer’s motherboard or it can be provided by a modular NIC (network interface card), also called a network adapter, installed in an expansion slot on the motherboard. Both ports are typically called NICs.

A LAN can have several switches daisy-chained together. The backbone is a central conduit that connects the segments (pieces) of a network and is sometimes referred to as “a network of networks.” The backbone might use higher transmission speeds and different cabling than network cables connected to computers. Daisy-chained switches use a bus topology, but each switch connects to computers via a star topology, making it a hybrid topology.

A central switch can connect to multiple peripheral switches, forming a hub-and-spoke topology. The central switch is the hub, and each peripheral switch is a spoke.

A router manages traffic between two or more networks and can help find the best path for traffic to get from one network to another. SOHO (small office-home office) networks use a consumer grade router to connect the LAN to the Internet.

Legacy Networking: Ring Topology

In a ring topology, nodes are connected in a ring, with one node connecting only to its two neighboring nodes. A node can put data on the ring only when it holds a token. The ring topology is rarely used today because of its slow speed and vulnerability to failure.

Routers

An enterprise or industrial-grade router can have several network ports, one for each of the networks it connects to. The router belongs to each of these networks. The fundamental difference between a switch and a router is that a switch belongs only to its local network, and a router belongs to two or more networks. Routers act as a gateway between multiple networks.

Hosts vs. Nodes

A host is any endpoint device, such as a computer or printer, connected to a network that hosts or accesses a resource. A node is any device, such as a router or switch, connected to a network that can be addressed on the local network or managed through a network connection.

A client computer or server is both a node and a host, but a router or switch does not normally host resources and is, therefore, merely a node on the network.

Hosts are typically networked devices (endpoint devices), while nodes can be either end devices or intermediary devices. Cisco standards call end devices hosts, and intermediary devices nodes.

MANs and WANs

A group of LANs that spread over a wide geographical area is called a WAN (wide area network). A group of connected LANs in the same geographical area is known as a MAN (metropolitan area network) or CAN (campus area network).

WANs and MANs often use different transmission methods and media than LANs do. The Internet is the largest and most varied WAN in the world.

Other network types include:

• PAN (personal area network): A network of personal devices.
• BAN (body area network): Made up of personal fitness devices.
• SAN (storage area network): Consists of high-capacity data storage devices in a defined network segment.
• WLAN (wireless local area network): Consists of two or more devices connected wirelessly.

The Seven-Layer OSI Model

An application, such as a browser, depends on operating systems to communicate across the network. Operating systems depend on hardware to communicate across the network. Protocols govern each layer of communication.

A seven-layer model, the OSI (Open Systems Interconnection) reference model, was developed to categorize the layers of network communication. It was first developed by the International Organization for Standardization (ISO).

OSI Model Layers:

1. Layer 7: Application Layer: Describes the interface between two applications on separate computers. This layer does not contain the applications themselves. Examples of protocols used at this layer are HTTP, SMTP, POP3, IMAP4, DNS, FTP, Telnet, SSH, and RDP. Data passed between applications and the OS is called a payload.
2. Layer 6: Presentation Layer: Responsible for reformatting, compressing, and/or encrypting data in a way that the application on the receiving end can read. For example, an email message can be encrypted at the presentation layer by the email client or by the OS.
3. Layer 5: Session Layer: Describes how data between applications is synced and recovered if messages don’t arrive intact. For example, the Zoom application works with the OS to establish and maintain a session between two endpoints. Tasks for each layer may be performed by the OS or the application. An API (application programming interface) is an access point into a software’s available processes.
4. Layer 4: Transport Layer: Responsible for transporting application layer payloads from one application to another. The two main transport layer protocols are TCP (guarantees delivery) and UDP (does not).
   • TCP (Transmission Control Protocol): Connection-oriented protocol that makes a connection with the end host, checks whether the data is received, and resends it if it is not. TCP is used by applications such as web browsers and email. If the message is too large to transport in one package across the network, TCP divides it into smaller messages called segments.
   • UDP (User Datagram Protocol): Connectionless protocol that does not guarantee delivery because it doesn’t maintain a connection to check whether data is received. UDP is used for broadcasting, such as streaming video or audio over the web or also used to monitor network traffic. If the message is too large to transport in one package across the network, UDP divides it into smaller messages called datagrams..

Transport-layer protocols add control information in an area at the beginning of the payload called the header. Encapsulation is the process of adding a header to the data inherited from the layer above. The transport layer header addresses the receiving application by a number called a port.

5. Layer 3: Network Layer: Responsible for moving messages from one node to another until they reach the destination host. This is the layer where routers typically function. The principal protocol is IP (Internet Protocol). IP adds its own network layer header to the segment or datagram, and the entire network layer message is now called a packet. The network layer header identifies the sending and receiving hosts by their IP addresses. Packets that are larger than the maximum size are divided into smaller packets in a process called fragmentation.
   • IP relies on supporting protocols to find a route for a packet when traversing several networks on its way to its destination. Ex: ICMP (Internet Control Message Protocol) and ARP (Address Resolution Protocol).
6. Layer 2: Data Link Layer: Commonly called the link layer. This layer, and layer 1, are responsible for interfacing with the physical hardware on the local network. The type of networking hardware or technology used on a network determines the data link layer protocol used. Examples of data link layer protocols are Ethernet and Wi-Fi.

The data link layer puts its own control information in a data link layer header and attaches control information to the end of the packet in a trailer. The entire data link layer message is then called a frame. The frame header contains the hardware addresses of the source and destination NICs, also called a MAC (Media Access Control) address, physical address, hardware address, or data link layer address. These physical addresses are short-range addresses used only to find nodes on the local network.
* Firmware: Programs embedded into hardware devices. This software does not change unless a firmware upgrade is performed.

7. Layer 1: Physical Layer: Responsible for sending bits via a wired or wireless transmission. These bits can be transmitted as wavelengths in the air (for example, Wi-Fi), voltage on a copper wire (for example, Ethernet on twisted-pair cabling), or light (for example, Ethernet on fiber-optic cabling).

Protocol Data Unit (PDU)

A group of bits as it moves from one layer to the next and from one LAN to the next is called a PDU (protocol data unit).

How Layers Work Together

In summary, the sending host encapsulates the payload in headers and a trailer before sending it. The receiving host removes the headers and trailer in reverse order before the message reaches the web server application.

TCP/IP Model

A four-layer model similar to the OSI model is the TCP/IP model. The four layers are application layer, transport layer, Internet layer, and link layer. This course and the CompTIA Network+ exam use the OSI model.

Safety Procedures and Policies

As a network and computer technician, you need to know how to protect yourself and sensitive electronic components as you work. Let’s look at some best practices for safety.

Emergency Procedures

In case of an emergency, such as a fire alert, you need to know the best escape route or emergency exit. Review building layouts and fire escape plans and be aware of emergency exit doors.

Fire Suppression Systems

A company is likely to have at least one fire suppression system in its data center that provides fire protection at the following levels:

• Building level: Protects the building and employees.

  • Active fire protection: Ex: fire extinguishers
  • Passive fire protection: Ex: firewalls

• Room level: Incorporates a sprinkler or gas system with at least two detection points to activate the system; gas systems decrease oxygen levels or absorb heat.

  • *Ex: the popular FM-200

• Rack level: Offers targeted fire detection and suppression inside the cabinet that holds network devices.

Other components:

• Emergency alert system: Loud noise, flashing lights, text and voice message alerts.
• Portable fire extinguishers: Electrical fires require a Class C fire extinguisher.
• Emergency power-off switch: Use only when necessary.

Fail Open or Fail Close

• During a fire alert using a fail-open policy, all exit doors stay unlocked so that people can safely leave the building and firefighters can enter the building
• If firewall software protecting access to a database of customer credit card numbers fails, it might be configured to fail close and to deny access toaccess to the database unitl software is back online.

SDS (Safety Data Sheet)

An SDS (safety data sheet), formerly called an MSDS (material safety data sheet), explains how to properly handle substances such as chemical solvents and how to dispose of them. It includes information such as identification, first-aid measures, fire-fighting measures, accidental release measures, handling and storage guidelines, exposure controls, and physical and chemical properties.

OSHA (Occupational Safety and Health Administration) guidelines when using power or hand tools:

• Wear PPE (personal protective equipment).
• Keep all tools in good condition and properly store tools not in use.
• Use the right tool for the job and operate the tool according to the manufacturer’s instructions and guidelines. Don’t work with a tool unless you are trained and authorized to use it.
• Watch out for trip hazards.

Lifting Heavy Objects

1. Decide which side of the object to face so that the load is the most balanced.
2. Stand close to the object with your feet apart.
3. Keeping your back straight, bend your knees, and grip the load.
4. Lift with your legs, arms, and shoulders, and not with your back or stomach.
5. Keep the load close to your body and avoid twisting your body while you’re holding it.
6. To put the object down, keep your back as straight as you can and lower the object by bending your knees.

Protecting against Static Electricity

Computer components are grounded inside a computer case.

Sensitive electronic components can be damaged by ESD (electrostatic discharge). ESD can cause catastrophic failure or upset failure.

Ground yourself using one of these methods:

• Wear an ESD strap around your wrist that clips onto a metallic part of the computer case, called a chassis, which eliminates any ESD between you and the chassis and its components.
• If you don’t have an ESD strap handy, be sure to keep touching the metal parts of the case before you touch any component inside the case. This reduces the risk of ESD.
• To protect a sensitive component, always store it inside an antistatic bag (but not on top of the bag) when it’s not in use.

Always shut down and unplug a computer before working inside it.

Troubleshooting Network Problems

Troubleshooting Model (Seven Steps):

1. Identify the problem and its symptoms: Identify the symptoms, question the user, find out what has recently changed, and determine the scope of the problem. Duplicate the problem if possible.
2. Establish a theory of probable cause: Make your best guess as to the source of the problem. Consider multiple approaches, such as working through the layers of the OSI model.
   • Follow the bottom-to-top OSI model by first suspecting and eliminating failed hardware.
   • Obvious software related: Follow the OSI model top-to-bottom.
3. Test your theory to determine the cause:Test to assure yourself that it will solve the problem before you implement the solution, and then determine the next steps needed. Escalate the problem to the next tier of support if the test fails.
4. Establish a plan for resolving the problem: Consider the scope of your change, especially how it will affect users, their applications, and their data. Make changes when the least number of users are on the network and follow change management procedures.
5. Implement the solution or escalate the problem: Alert all affected users in advance, create backups of software and data, and keep notes as you work. Make only one change at a time and test it before moving to another change. Escalate complex problems.
6. Verify functionality and implement preventive measures: Test the system for full system functionality. Consider what you can do to make sure the problem doesn’t reappear
7. Document findings, actions, and outcomes: Use a call tracking system (help desk software) to document problems and their resolutions. your company may also require you to document lessons learned and unique or insightful solutions to problems in your company’s knowledge base for you and others to draw from in the future.