Flash Card #1 || Basic Networking
This section reviews the foundational functions of networking, including the OSI model and the TCP/IP model.
Question 1 What is a network?
Answer 1
A network is a collection of devices and end systems.
Networks consist of computers, servers, and network devices, such as switches, routers, wireless access points, and firewalls that are interconnected, communicating with each other and sharing resources with each other. They are found in homes, small business, and large enterprises.
Question 2 What four major categories make up the physical components of a network?
Answer 2
The four major categories found in networks are
- Â Endpoints: These devices receive data and are endpoints of the network. Examples include PCs, servers, laptops, tablets, and so on.
- Â Interconnections: The components that provide a means for data to travel across the network. This includes network interface cards (NIC), network media, and connectors.
- Â Switches: Provide network access for compute devices and other network devices.
- Â Routers: Interconnect networks.
Question 3 What are the four major resources that are shared on a computer network?
Answer 3
The four major resources that are shared on a computer network are as follows:
- Â Data and applications: Consist of computer data and network-aware applications such as e-mail
- Â Resources: Include input and output devices such as cameras and printers
- Â Network storage: Consists of directly attached storage devices (physical storage that is directly attached to a computer and a shared server), network attached storage, and storage-area networks
- Â Backup devices: Can back up files and data from multiple computers
Question 4 What are common network user applications on today’s networks?
Answer 4
Common network user applications on today’s networks are
- Â Email
- Â Web (this includes web applications or any application the uses HTTP/HTTPS)
- Â Instant messaging
- Â Video/collaboration
- Â Databases
- Â File sharing
Question 5 List three categories of network applications.
Answer 5
Three categories of network applications are as follows:
- Â Batch applications: Examples are FTP and TFTP. They are started by a person and complete with no other interaction. Bandwidth is important but not critical.
- Â Interactive applications: Include database updates and queries. A person requests data from a server and waits for a reply. Response time depends more on the server and storage than the network.
- Â Real-time applications: Include VoIP and video. Network bandwidth is critical because these applications are time sensitive. Quality of service (QoS) and sufficient network bandwidth are mandatory for these applications.
Question 6 What are three types of network-monitoring software?
Answer 6
Three types of network-monitoring software are
- Â Protocol analyzers: Capture network packets between network devices and decode the packets so that one can view what applications are being transmitted on a network.
- Â Sniffers: Work like a wiretap and allow one to observe network communication and view the data that is being transmitted.
- Â Availability and performance programs: Use protocols use as ICMP and SNMP to view the availability of network devices and performance in real time.
Question 7 Your company wants to provide streaming video services to all branches and sales representatives. What two network characteristics are the most critical to achieving this goal?
Answer 7
The most critical characteristics are bandwidth and latency.
Time-sensitive applications such as video and VoIP are dependent on bandwidth and latency to function properly. When implementing time-sensitive applications, one needs to ensure that the network has enough bandwidth and low delay to ensure a proper end-user experience.
Question 8 When describing the characteristics of a network, what does speed refer to?
Answer 8
Speed refers to how fast data is transmitted over the network.
Today’s networks consist of speeds of 100 Mbps, 1Gbps, 10 Gbps, 40 Gbps, and 100 Gbps.
Question 9 When describing the characteristics of a network, what does cost refer to?
Answer 9
Cost refers to the general financial value of network components, installation, and maintenance.
Note
Do not confuse this with cost that is associated with dynamic routing protocols such as OSPF.
Question 10 When describing the characteristics of a network, what does security refer to?
Answer 10
Security refers to protecting the network devices and data from both internal and external sources.
Question 11 When describing the characteristics of a network, what does availability refer to?
Answer 11
Availability is the measurement of the network uptime compared to its downtime.
Network availability percentage can be calculated using the following formula, which calculates the number of minutes of downtime compared to the number of minutes in a year:
([525,600 – Minutes downtime] / [525,600]) * 100
Question 12
Your CIO wants to know the network availability of your company’s network for the past year. During the past year, the network was down for 30 minutes. What was the total availability of the network?
Answer 12
The total availability was 99.994%.
([525,600 – 30] / [525,600]) * 100 = 99.994%
Note
Network availability percentage is calculated using the following formula, which calculates the number of minutes of downtime compared to the number of minutes in a year:
([525,600 – Minutes downtime] / [525,600]) * 100
Question 13 When describing the characteristics of a network, what does scalability refer to?
Answer 13
Scalability refers to how well the network can accommodate more users and more data—in other words, how easily the network can grow and expand.
Question 14 When describing the characteristics of a network, what does reliability refer to?
Answer 14
Reliability refers to the dependability of the devices that make up the network (switches, routers, computers, servers, access points, software, and so on).
Question 15 What is the difference between the physical and logical network topology?
Answer 15
Physical topology defines the physical layout of devices and network media—cables, network devices, computers, and so on—and how these components are physically connected and configured.
Logical topology refers to the data path or logical paths of the network in which data accesses the media and transmits packets across it. This includes IP addresses as well as routing paths.
Question 16 What are the six types of physical topologies implemented in today’s networks?
Answer 16
The six types of physical topologies implemented in today’s networks are
- Star
- Extended star
- Mesh
- Partial mesh
- Bus
- Ring
Note
See the study sheets located at the back of the flash cards for a diagram of each of these physical topologies.
Question 17 What physical network topology connects all devices to one cable?
Answer 17
The bus topology connects all devices to one cable.
This cable connects one computer to another. In a logical bus topology, only one packet can be transmitted at a time.
Question 18 Describe a ring physical network topology.
Answer 18
In a ring topology, all hosts and devices are connected in the form of a ring or circle. The following two types of ring networks exist:
- Â Single-ring: In a single-ring network, all devices share a single cable and data travels in one direction. Each device waits its turn to send data over the network.
- Â Dual-ring: A dual-ring network has a second ring to add redundancy and allows data to be sent in both directions.
Question 19 Describe a star and extended star physical topology.
Answer 19
Star and extended star physical topologies are made up of a central connection point, such as a hub or switch, where all cable segments connect. A star topology resembles spokes in a bicycle wheel and is the network topology of choice in Ethernet networks.
When multiple star topologies are connected to a common independent centralized device, it is called an extended star topology.
Question 20 What physical network topology connects all devices to each other?
Answer 20
A mesh network topology connects all devices to each other for fault tolerance and redundancy.
Question 21 What is the difference between a full-mesh and a partial-mesh topology?
Answer 21
A full-mesh topology connects all nodes to one another for full redundancy. In a partial-mesh topology, at least one node maintains multiple connections to all other devices and one node cannot connect to all other nodes as well.
Question 22 What are the seven layers of the OSI reference model? Include the layer number and name of each layer in your answer.
Answer 22
The seven layers of the OSI reference model are as follows:
- Layer 7: Application layer
- Layer 6: Presentation layer
- Layer 5: Session layer
- Layer 4: Transport layer
- Layer 3: Network layer
- Layer 2: Data link layer
- Layer 1: Physical layer
Question 23 What are six reasons that the OSI reference model was created?
Answer 23
Six reasons that the OSI reference model was created are as follows:
1. To ensure that different vendors’ products can work together
2. To create standards to enable ease of interoperability by defining standards for the operations at each level
3. To clarify general functions of internetworking
4. To divide the complexity of networking into smaller, more manageable sublayers
5. To simplify troubleshooting
6. To enable developers to modify or improve components at one layer without having to rewrite an entire protocol stack
Question 24 What is the function of the physical layer (Layer 1) in the OSI model? Give some examples of physical layer implementation.
Answer 24
The physical layer defines the physical medium. It defines the media type, the connector type, and the signaling type (baseband versus broadband). This includes voltage levels, physical data rates, and maximum cable lengths. The physical layer is responsible for converting frames into electronic bits of data, which are then sent or received across the physical medium. Twisted-pair, coaxial, and fiber-optic cable operate at this level. Other implementations at this layer are repeaters/hubs.
Question 25 What is the responsibility of the data link layer (Layer 2)?
Answer 25
The data link layer defines how data is formatted from transmission and how access to the physical media is controlled. This layer also typically includes error correction to ensure reliable delivery of data.
The data link layer translates messages from the network layer into bits for the physical layer, and it enables the network layer to control the interconnection of data circuits within the physical layer. Its specifications define different network and protocol characteristics, including physical addressing, error notification, network topology, and sequencing of frames.
Data-link protocols provide the delivery across individual links and are concerned with the different media types, such 802.3. The data link layer is responsible for putting 1s and 0s into a logical group. These 1s and 0s are then put on the physical wire. Some examples of data link layer implementations are IEEE 802.3, packet trailer (for Ethernet, frame check sequence [FCS] or cyclic redundancy check [CRC]), Fiber Distributed Data Interface (FDDI), High-Level Data Link Control (HDLC), and Frame Relay.
Question 26 The Institute of Electrical and Electronics Engineers (IEEE) defines what sublayer of the data link layer?
Answer 26
The IEEE defines the Media Access Control (MAC) sublayer of the data link layer.
Question 27 What functions does the Media Access Control (MAC) sublayer provide?
Answer 27
The MAC sublayer specifies how data is placed and transported over the physical wire. It controls access to the physical medium.
The MAC sublayer communicates downward directly to the physical layer. Physical addressing (MAC addresses), network topologies, error notification, and delivery of frames are defined at the MAC sublayer.
Question 28 What are examples of network devices that operate at the data link layer (Layer 2)?
Answer 28
Bridges and switches operate at the data link layer.
Both devices make decisions about what traffic to forward or drop (filter) by MAC addresses; logical network address are not used at this layer. Data link layer devices assume a flat address space.
Question 29 Describe the function of the network layer (Layer 3) of the OSI model. Give some examples of network layer implementations.
Answer 29
The network layer provides internetwork routing and logical network addresses. It defines how to transport traffic between devices that are not locally attached.
The network layer also supports connection-oriented and connectionless service from higher-layer protocols.
Routers and multilayer switches operate at the network layer. IP and IPv6 are examples of network layer implementations.
Question 30 Are network layer addresses physical or logical?
Answer 30
Network layer addresses are logical.
These addresses are logical addresses that are specific to the network layer protocol being run on the network. Each network layer protocol has a different addressing scheme. They are usually hierarchical and define networks first and then hosts or devices on that network. An administrator typically assigns network layer addresses either by static configuration or dynamic configuration.
An example of a network address is an IP address. For example, IPv4 has 32-bit addresses often expressed in decimal format. An example of an IPv4 address in decimal format is 192.168.0.1.
Question 31 What is the transport layer (Layer 4) of the OSI model responsible for? Give some examples of transport layer implementations.
Answer 31
The transport layer segments and reassembles data from upper-layer applications into data streams. It provides reliable data transmission to upper layers.
End-to-end communications, flow control, multiplexing, error detection and correction, and virtual circuit management are typical transport layer functions. Some examples include Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).
Note
Not all transport protocols perform error detection and correction. For example, UDP does not perform error detection or correction.
Question 32 What layer of the OSI model handles the reliability of network communications between hosts using flow control, sequencing, and acknowledgments?
Answer 32
The transport layer handles this reliability.
The transport layer uses acknowledgments and sequence numbers for reliable delivery of data. Flow control is used to avoid network or host congestion.
Question 33 What is flow control, and what are the three methods of implementing it?
Answer 33
Flow control is the method of controlling the rate at which a computer sends data, thus preventing network congestion.
The three methods of implementing flow control are as follows:
- Buffering
- Congestion avoidance
- Windowing
Question 34 How do network devices use buffering for flow control?
Answer 34
Buffering is used by network devices to temporarily store bursts of extra data in memory until they can be processed and sent. Buffering can handle occasional data bursts; however, buffer overflows can occur if data bursts are continuous.
Question 35 What are the functions of the session layer (Layer 5) of the OSI model? Provide some examples.
Answer 35
The session layer is responsible for creating, managing, and ending communication sessions between presentation layer entities.
These sessions consist of service requests and responses that develop between applications located on different network devices. Some examples include Structured Query Language (SQL), remote-procedure call (RPC), and SSL.
Question 36 What is the responsibility of the presentation layer (Layer 6)? Give some examples of Layer 6 implementations.
Answer 36
Also known as the translator, the presentation layer provides coding and conversion functions to application layer data. This guarantees that the application layer on one system can read data transferred from the application layer of a different system. Some examples of the presentation layer are
Compression, decompression, and encryption
JPEG, TIFF, GIF, PICT, QuickTime, MPEG, EBCDIC, and ASCII file types
Question 37 What does the application layer (Layer 7) of the OSI model do, and what are some examples of this layer?
Answer 37
The application layer is the layer that is closest to the user. This means that this layer interacts directly with the software application. The application layer’s main functions are to identify and establish communication partners, determine resource availability, and synchronize communication. Some examples include TCP/IP applications protocols such as Telnet, FTP, Simple Mail Transfer Protocol (SMTP), and HTTP.
Note
An application must have a communicating component, such as FTP, to be relevant to internetworking.
Question 38 How do the different layers of the OSI model communicate with each other?
Answer 38
Each layer of the OSI model can communicate only with the layer above it, below it, and parallel to it (a peer layer on a remote host).
For example, the presentation layer can communicate with only the application layer and session layer on the local host, and the presentation layer on the remote host. These layers communicate with each other using service access points (SAP) and protocol data units (PDU). The SAP is a conceptual location at which one OSI layer can request the services of another OSI layer. PDUs control information that is added to the user data at each layer of the model. This information resides in fields called headers (the front of the data field) and trailers (the end of the data field).
Note
SAPs apply to OSI layer application protocols and do not apply to TCP/IP.
Question 39 Which layer of the OSI model uses the hardware address of a device to ensure proper message delivery to a host on a LAN?
Answer 39
The data link layer uses physical addresses or hardware addresses for message delivery on a LAN.
Question 40 Which network layer protocols are responsible for path determination and traffic switching?
Answer 40
Routing protocols are responsible for path determination and traffic switching.