N10-009 Networking Concepts Study Guide for the CompTIA Network+

General Information

This is study material for the CompTIA Network+ N10-009 exam, which replaces the old Network+ N10-008 exam as of December 20, 2024. Be sure you are studying for the right test.

Nearly one-fourth of the questions on the CompTIA Network+ N10-009 exam assess networking concepts, so your understanding in this realm is important. Just a little over 12% of these questions begin with a scenario, so most of them simply test your knowledge of basic networking ideas and terms.

The Open Systems Interconnection (OSI) Reference Model

The OSI model, developed by the International Organization for Standardization (ISO), is the most frequently used reference model for network communication design. A reference model is a map or blueprint of how communications take place between devices. The OSI model was developed to create a standard communication pattern that could be used by all vendors to create an interoperable network by separating processes into logical groupings, or layers. The OSI model is composed of seven logical groupings known by both their layer number and their purpose. You will need to be able to compare and contrast the seven layers of the OSI model and their related concepts.

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Layer 1—Physical

Layer 1, or the physical layer, defines the physical topology of a network, meaning how the physical cables and devices are arranged and connected. Logically, the physical layer receives and sends data in bits, which only transmit in binary, the base language of all computing devices. The physical layer sends or receives the binary and passes it up to the data link layer.

Layer 2—Data Link

Layer 2, or the data link layer, receives the bits from the physical layer and is responsible for the physical transmission of the data to the appropriate devices or locations through the use of hardware (or Ethernet) addresses, such as media access control (MAC) or logical link control (LLC) addresses. The data link layer also provides the network topology and is responsible for flow control. This layer takes the bits sent by the physical layer, combines them into bytes (eight bits), and places them into data frames. A header is placed on the data frame by the data link layer, which contains the destination and source hardware addresses, and the data frame is then passed up to Layer 3.

Layer 3—Network

Layer 3, or the network layer, is responsible for the logical device addressing on a network as well as their location and the most effective way of getting the data to where it needs to go. When the network layer receives the data frame, the header placed on the data is removed, and the logical destination address contained in the original data is evaluated and routed (in a packet) to the appropriate location, where it is passed up to Layer 4. The most common networking protocol is the Internet Protocol (IP).

Layer 4—Transport

Layer 4, or the transport layer, is responsible for turning received packets into a data stream via segments, which provides the logical connection between the lower three layers and the upper three layers. The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) are the most commonly used transport protocols.

Layer 5—Session

Layer 5, or the session layer, receives the segments sent by Layer 4 and creates a separate communication connection between the transport layer and the presentation layer entities. The session layer is primarily responsible for keeping the data from one application separate from other applications.

Layer 6—Presentation

Layer 6, or the presentation layer, receives the data sent to it through the created session, which is still in a binary format, and performs the data translation and code formatting, which is used by Layer 7. The presentation layer is also responsible for data compression, decompression, encryption, and decryption.

Layer 7—Application

Layer 7, or the application layer, takes the data that was translated by Layer 6 and uses it to create the user interface. The application layer is responsible for creating the connection between applications and the operating system (OS) via application processes, interfaces, or an application programming interface (API).

Networking Appliances, Applications, and Functions

A networking device is an electronic device, either hardware or software, that facilitates communication and interaction between two or more devices on a network. Networking devices are used for data transmission through a network, with each device transmitting data based on their specific function. There are numerous network devices that you should be familiar with for the CompTIA Network+ N10-009 exam. You need to be able to compare and contrast different appliances, their common functions, and the appropriate applications for each device on a network.

Physical and Virtual Appliances

In a modern network, networking devices can be either physical devices or virtual devices. Virtual networking devices may be provided through a cloud service provider or within an on-premises network using virtualization techniques.

Router

A router is used for connecting two or more network segments together, creating an internetwork. A router uses IP information to transmit data to the appropriate location on the network. The router is the networking device that provides the connection to the internet. In network diagrams, the following universal symbol is used to indicate a router:

Switch

A switch connects multiple devices on a network and forwards data between devices on a network based on the source and destination information attached to the data, including assigned port numbers. A Layer 2 switch is a traditional switch that uses Layer 2 hardware addresses (MAC addresses) to forward data through the network. A Layer 3 switch is one that is capable of performing the functions of both a traditional switch as well as a router, which forwards data at the network layer. In network diagrams, the following universal symbol is used to indicate a switch:

Firewall

A firewall is a networking security device that monitors and filters incoming and outgoing traffic based on preset parameters. A firewall can be implemented at multiple layers of the OSI model depending on functionality needs. In a network diagram, the following symbol (or something similar) is used to indicate a firewall:

Intrusion Prevention System (IPS)/Intrusion Detection System (IDS)

An IPS or IDS device is a Layer 3 networking security device that monitors network transmissions for malicious activity. An IPS device is inline and can actively prevent malicious traffic, while an IDS device sits outside the flow and only collects and monitors traffic flow data.

Load Balancer

A load balancer distributes traffic between two or more devices attached to a single IP address. A traditional load balancer functions in Layer 4 and distributes traffic based on a distribution configuration, such as round-robin or least number of connections. In a network diagram, the following universal symbol is used to indicate a load balancer:

Proxy

A proxy or proxy server provides an interface between a client requesting a resource (endpoint device) and the server housing that resource (the internet). A proxy resides at Layer 7 and can be either forward, in which the proxy sits in front of the client, or reverse, in which the proxy sits in front of the web server. This is an illustration of a forward proxy:

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This is an illustration of a reverse proxy:

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Network-Attached Storage (NAS)

NAS is a file storage bank that is shareable between numerous devices on a network via a LAN connection, accessible either through a wired or wireless connection

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Storage Area Network (SAN)

A SAN is a network of high-speed storage devices that is not located on the local area network (LAN) but is accessible via a dedicated storage-specific switch. A SAN provides a network with a pooled storage space that can be used to collect, manage, and access data from multiple network-attached servers or devices.

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Wireless

Wireless networking appliances are devices that provide a point of contact for wireless connections between endpoint devices and the primary network.

Access Point (AP)

An AP, also known as a wireless AP or WAP, is a Layer 2 networking device that connects devices wirelessly to a wired network connection or router. Some APs can be used to connect to a separate router or may have routing functionality integrated, which is commonly referred to as a wireless router. In a network diagram, the following symbol can be used to indicate an access point:

Controller

A wireless LAN controller (WLC) centralizes multiple access points into a single device or controller. It is used to manage and configure all connected APs. A WLC functions in both Layer 2 and Layer 3. In a network diagram, the following symbol is commonly used to indicate a WLC:

Applications

Applications are the processes, interfaces, and APIs through which an end user communicates with the OS of the endpoint device and the network. Applications are used to identify and establish the connection with the target while also evaluating for required resources.

Content Delivery Network (CDN)

A CDN is a bank of connected servers in different geographical locations that store website content, decreasing the time it takes for end users to access and communicate with the primary network containing the web data. A CDN is able to cache data, reduce latency, and scale quickly to meet demand.

Functions

Network appliances provide various network functions to create, maintain, and secure communications. Network functions, like networking devices, may also be accessed via a wired or wireless connection.

Virtual Private Network (VPN)

A VPN is a virtual environment that creates a secure connection between entities over public or insecure network connections. The VPN verifies and establishes the secure connection prior to routing traffic through the VPN tunnel.

Quality of Service (QoS)

QoS is the concept of prioritizing network traffic to ensure that critical network applications, users, or data flows can maintain connection with the network. QoS can be programmed to address connectivity issues such as dropped packets, delays, jitter, and errors in data transmission.

Time to Live (TTL)

The TTL is a time value applied to data, such as cache data, that indicates how long the receiving entity can store the result before a new request needs to be submitted. For example, if the response provided by the web server has a TTL of one hour, the local device will store the cached information for one hour in its local cache before forgetting the information.