Networking Concepts

Wireless Local Area Network (WLAN)

A wireless network designed to replace or supplement a wired local area network (LAN). uses radio waves to transmit data between wireless devices.

Personal Area Network (PAN)

provides communication for devices owned by a single user that work over a short distance. connects devices, such as mice, keyboards, printers, smartphone, and tablets within the range of an individual person. All of these devices are dedicated to a single host and are most often connected with Bluetooth technology

Cellular Generations

1G/2G description, the first generation (1G) of cell phones were analog voice calls only.2G introduced digital voice, conference calls, and caller ID.Speed: less than 9.6 Kb/s. 2.5G description, .5G supports web browsing, short audio and video clips, games, and downloads of applications and ring tones.Speed: 9.6 Kb/s to 237 Kb/s. 3G description, 3G supports full-motion video, streaming music, 3D gaming, and faster web browsing.Speed: 144 Kb/s to 2 Mb/s. 3.5G description, 3.5G supports high-quality streaming video, high-quality video conferencing, and Voice over IP (VoIP).VoIP is a technology that applies internet addressing to voice data.Speed: 400 Kb/s to 16 Mb/s. 3.5G description, 3.5G supports high-quality streaming video, high-quality video conferencing, and Voice over IP (VoIP).VoIP is a technology that applies internet addressing to voice data.Speed: 400 Kb/s to 16 Mb/s. 4G description, 4G supports IP-based voice, gaming services, high-quality streamed multimedia, and Internet Protocol version 6 (IPv6). IPv6 is the newest version of internet addressing.No cell phone carriers could meet the 4G speed standards when first announced in 2008. Speed: 5.8 Mb/s to 672 Mb/s. LTE description, Long Term Evolution (LTE) is a designation for a 4G technology that meets the 4G speed standards.An advanced version of LTE significantly improves the speeds while the user is moving at high speeds, such as in a car on the highway.Speed: 50 Mb/s to 100 Mb/s when mobile, and up to 1 Gb/s when stationary. 5G description, The 5G standard was ratified in June 2018 and is currently being implemented in select markets.5G supports a wide variety of applications including augmented reality (AR), virtual reality (VR), smart homes, smart cars, and any scenario where data transfer occurs between devices.Speed: 400 Mb/s to 3 Gb/s download; 500 Mb/s to 1.5 Gb/s upload.

Virtual LAN (VLAN)

A technology that allows scattered users to be logically grouped together even though they may be attached to different switches. provides more efficient forwarding of data by isolating traffic to only those areas where it is required.

Bluetooth

A Bluetooth device can connect up to seven other Bluetooth devices. Described in the IEEE standard 802.15.1, Bluetooth devices operate in the 2.4 to 2.485 GHz radio frequency range and is typically used for PANs. The Bluetooth standard incorporates Adaptive Frequency Hopping (AFH). AFH allows signals to "hop" around using different frequencies within the 2.4 to 2.485 GHz range, thereby reducing the chance of interference when multiple Bluetooth devices are present.

Cable

A cable internet connection does not use telephone lines. Cable uses coaxial cable lines originally designed to carry cable television. A cable modem connects your computer to the cable company. You can plug your computer directly into the cable modem. However, connecting a routing device to the modem allows multiple computers to share the connection to the internet.

DHCP Server

A host needs IP address information before it can send data on the network. Two important IP address services are Dynamic Host Configuration Protocol (DHCP) and Domain Name Service (DNS). DHCP is the service used by ISPs, network administrators, and wireless routers to automatically assign IP addressing information to hosts

Metropolitan Area Network (MAN)

A large computer network usually spanning a city. Most colleges, universities, and large companies that span a campus use an infrastructure supported by a MAN. consists of various building connected through wireless or fiber optic media

Network Interface Card (NIC)

A network interface card (NIC) provides the physical connection to the network at the PC or other end device. As shown in the figure, there are different types of NICs. Ethernet NICs are used to connect to Ethernet networks and wireless NICs are used to connect to 802.11 wireless networks. Most NICs in desktop computers are integrated into the motherboard or connected to an expansion slot. NICs are also available in a USB form factor. A NIC also performs the important function of addressing data with the NIC's media access control (MAC) address and sending the data out as bits on the network. NICs found on most computers today are gigabit Ethernet (1000 Mbps) capable. Note: Today's computers and motherboards typically have NICs built in including wireless capability. Refer to the manufacturer's specifications for more information.

Wide Area Network (WAN)

A network that connects devices in geographically separated areas. Individuals and organizations contract for WLAN access from a service provider. Your service provider for your home or mobile device connects you to the largest WLAN, the internet.

Virtual Private Network (VPN)

A private data network that creates secure connections, or "tunnels," over regular Internet lines securely connects other network over an insecure network such as the internet. The most common type of VPN is used by teleworkers to access a corporate private network. Teleworkers are network user that are offsite or remote.

authentication server

Access to network devices is typically controlled through authentication, authorization, and accounting services. Referred to as AAA or "triple A", these services provide the primary framework to set up access control on a network device. AAA is a way to control who is permitted to access a network (authenticate), what they can do while they are there (authorize), and track what actions they perform while accessing the network (accounting). In the figure, the remote client goes through a four-step process to authenticate with a AAA server and gain access to the network.

Analog Telephone

Analog telephone internet access can transmit data over standard voice telephone lines. This type of service uses an analog modem to place a telephone call to another modem at a remote site. This method of connection is known as dialup.

Bridge

Bridges were introduced to divide LANs into segments. Bridges keep a record of all the devices on each segment. A bridge can then filter network traffic between LAN segments. This helps reduce the amount of traffic between devices. For example, if PC-A needs to send a job to the printer, the traffic will not be forward to Segment 2. However, the server will also receive this print job traffic.

Satellite

Broadband satellite is an alternative for customers who cannot get cable or DSL connections. A satellite connection does not require a phone line or cable, but uses a satellite dish for two-way communication. The satellite dish transmits and receives signals to and from a satellite that relays these signals back to a service provider, as shown in the figure. Download speeds can reach up to 10Mb/s or more, while upload speed ranges about 1/10th of download speeds. It takes time for the signal from the satellite dish to relay to your ISP through the satellite orbiting the Earth. Due to this latency, it is difficult to use time-sensitive applications, such as video gaming, Voice over Internet Protocol (VoIP), and video conferencing.

broadband

Broadband uses different frequencies to send multiple signals over the same medium. For example, the coaxial cables used to bring cable television to your home can carry computer network transmissions at the same time as hundreds of TV channels. Your cell phone can receive voice calls while also using a web browser. Some common broadband network connections include cable, digital subscriber line (DSL), ISDN, satellite, and cellular.

Cellular

Cell phone technology relies on cell towers distributed throughout the user's coverage area to provide seamless access to cell phone services and the internet. With the advent of the third-generation (3G) of cellular technology, smartphones could access the internet. Download and upload speeds continue to improve with each iteration of cell phone technology. In some regions of the world, smartphones are the only way users access the internet. In the United States, users are increasingly relying on smartphones for internet access. According to the Pew Research Center, in 2018 20% of adults in the United States do not use broadband at home (28% for adults 18-29). Instead, they use a smartphone for personal internet access. Search for "pew internet research" for more interesting statistics.

Network Media

Communication across a network is carried on a medium. The medium provides the channel over which the message travels from source to destination. The plural for medium is media.

Intermediary Devices

Computer networks contain many devices that exist in between the host devices. These intermediary devices ensure that data flows from one host device to another host device. The most common intermediary devices are shown in Figure 2: Switch - connects multiple devices to the network. Router - forwards traffic between networks. Wireless router - connects multiple wireless devices to the network and may include a switch to connect wired hosts. Access point (AP) - connects to a wireless router and is used to extend the reach of a wireless network. Modem - connects a home or small office to the Internet.

DNS server

DNS is the method computers use to translate domain names into IP addresses. On the internet, domain names, such as http://www.cisco.com, are much easier for people to remember than 198.133.219.25, which is the actual numeric IP address for this server. If Cisco decides to change the numeric IP address of www.cisco.com, it is transparent to the user because the domain name remains the same. The new address is simply linked to the existing domain name and connectivity is maintained.

Digital Subscriber Line (DSL)

DSL is an always-on service, which means that there is no need to dial up each time you want to connect to the internet. Voice and data signals are carried on different frequencies on the copper telephone wires. A filter prevents DSL signals from interfering with phone signals.

Mail Server

Email requires several applications and services, as shown in the figure. Email is a store-and-forward method of sending, storing, and retrieving electronic messages across a network. Email messages are stored in databases on mail servers. Email clients communicate with mail servers to send and receive email. Mail servers communicate with other mail servers to transport messages from one domain to another. An email client does not communicate directly with another email client when sending email. Instead, both clients rely on the mail server to transport messages. Email supports three separate protocols for operation: Simple Mail Transfer Protocol (SMTP), Post Office Protocol (POP), and Internet Message Access Protocol (IMAP). The application layer process that sends mail uses SMTP. A client retrieves email using one of the two application layer protocols: POP or IMAP.

Fiber

Fiber optic cables are made of glass or plastic and use light to transmit data. They have a very high bandwidth, which enables them to carry large amounts of data. At some point in your connection to the internet, your data will cross a fiber network. Fiber is used in backbone networks, large enterprise environments and large data centers. Older copper cabling infrastructures closer to home and businesses are increasingly being replaced with fiber. For example, in the figure, the cable connection includes a hybrid fiber coaxial (HFC) network in which fiber is used in the last mile to the user's home. At the user's home, the network switches back to copper coaxial cable. The choice of connection varies depending on geographical location and service provider availability.

Hub

Hubs receive data on one port and then send it out to all other ports. A hub extends the reach of a network because it regenerates the electrical signal. Hubs can also connect to another networking device, such as a switch or router, which connects to other sections of the network. Hubs are legacy devices and should not be used in today's networks. Hubs do not segment network traffic. When one device sends traffic, the hub floods that traffic to all other devices connected to the hub. The devices are sharing the bandwidth.

Intergrated Services Digital Network (ISDN)

Integrated Services Digital Network (ISDN) uses multiple channels and can carry different types of services; therefore, it is considered a type of broadband. ISDN is a standard that uses multiple channels to send voice, video, and data over normal telephone wires. ISDN bandwidth is larger than traditional dialup.

Line of sight wireless internet service

Line of sight wireless internet is an always-on service that uses radio signals for transmitting internet access, as shown in the figure. Radio signals are sent from a tower to the receiver that the customer connects to a computer or network device. A clear path between the transmission tower and customer is required. The tower may connect to other towers or directly to an internet backbone connection. The distance the radio signal can travel and still be strong enough to provide a clear signal depends on the frequency of the signal. Lower frequency of 900 MHz can travel up to 40 miles (65 km), while a higher frequency of 5.7 GHz can only travel 2 miles (3 km). Extreme weather conditions, trees, and tall buildings can affect signal strength and performance.

Mobile Hotspot and Tethering

Many cell phones provide the ability to connect other devices This connection, known as tethering, can be made using Wi-Fi, Bluetooth, or by using a USB cable. Once a device is connected, it is able to use the phone's cellular connection to access the Internet. When a cellular phone allows Wi-Fi devices to connect and use the mobile data network

Syslog server

Many networking devices support syslog, including routers, switches, application servers, firewalls, and other network appliances. The syslog protocol allows networking devices to send their system messages across the network to syslog servers. The syslog logging service provides three primary functions: The ability to gather logging information for monitoring and troubleshooting The ability to select the type of logging information that is captured The ability to specify the destinations of captured syslog messages

NFC (Near Field Communication)

NFC uses frequency 13.56 MHz and is a subset of the RFID standards. NFC is designed to be a secure method to complete transactions. For example, a consumer pays for good or services by waving the phone near the payment system. Based on a unique ID, the payment is charged directly against a pre-paid account or bank account. NFC is also used in mass-transportation services, the public parking sector, and many more consumer areas.

Port Numbers

Port number 20, Protocol TCP, Application FTP (data). File transfer protocol. Used to transfer files between computers. Considered insecure Port number 21, Protocol TCP, Application FTP (control). uses TCP port 21 to establish a connection between the client and FTP server. In order to start a data transfer session Port number 22, Protocol TCP, Application, SSH. Secure Shell or Secure Socket Shell provides a strong authentication and encrypted data transport between a client and remote computer. Like Telnet, it provides a command line on the remote computer. Port number 23, Protocol TCP, Application Telnet. Telnet is an insecure remote access protocol that provides a command line on a remote computer. SSH is preferred for security reasons. Port number 25, Protocol TCP, Application SMTP. Simple Mail Transfer Protocol is used to send email from clients to an email server. It may also be used to relay email messages from source to destination email servers. Port number 53, Protocol TCP/UDP, Application DNS, protocol finds the IP address associated with a registered Internet domain for Web, Email, and other Internet services. It uses UDP for requests and information transfer between DNS servers. TCP will be used for DNS responses if required Port number 67, Protocol UDP, Application DHCP (server). Dynamic Host Configuration Protocol automatically provides IP addresses to network hosts and provides a way to manage those addresses. Port number 68, Protocol UDP, Application DHCP (client). Dynamic Host Configuration Protocol automatically provides IP addresses to network hosts and provides a way to manage those addresses. Port number 69, Protocol UDP, Application TFTP. Trivial File Transfer Protocol utilizes less overhead than FTP. Port number 80, Protocol TCP, Application HTTP. Hypertext Transfer Protocol (HTTP) provides a set of rules for exchanging text, graphic images, sound, video, and other multimedia files on the World Wide Web. Port number 110, Protocol TCP, Application POP3. Post Office Protocol 3 is used by email clients to retrieve messages from an email server. Portnumber 137-139, Protocol TCP, UDP, Application NetBIOS/NetBT. NetBIOS over TCP/IP provides a system through which older computer applications can communicate over large TCP/IP networks. Different NetBT functions use different protocols and ports in this range. Port number 143, Protocol TCP, Application IMAP. Internet Message Access Protocol is used to retrieve email messages from a server. It is more advanced than POP3 and offers a number of advantages. Port number 161/162, Protocol UDP, Application SNMP. Simple Network Management Protocol enables network administrators to monitor network operations from centralized monitoring stations. Port number 389, Protocol TCP,UDP, Application LDAP. Lightweight Directory Access Protocol is used to maintain user identity directory information that can be shared across networks and systems. It can be used to manage information about users and network resources. It can be used to authenticate users on multiple computers. Port number 427, Protocol TCP,UDP, Application SLP. Service Location Protocol allows computers and other devices to locate services on a LAN without previous configuration. Usually uses UDP, but can use TCP. Port number 443, Protocol TCP, Application HTTPS. Secure HTTP Port number 445, Protocol TCP, Application SMB/CIFS. Server Message Block or Common Internet File System allow for sharing of files, printers, and other resources between nodes on a network. Port number 548, Protocol TCP, Application AFP. Apple Filing Protocol is a proprietary protocol developed by Apple to enable file services for macOS and classic Mac OS. Port number 3389, Protocol TCP,UDP, Application RDP. Remote desktop protocol was developed by Microsoft to provide remote access to the graphical desktop of a remote machine. It is useful for tech support situations, however it should be used with caution because it provides a remote user with complete control of the destination computer

Print Server

Print servers enable multiple computer users to access a single printer. A print server has three functions: Provide client access to print resources. Administer print jobs by storing them in a queue until the print device is ready for them and then feeding or spooling the print information to the printer. Provide feedback to users.

proxy server

Proxy servers have the authority to act as another computer. A popular use for proxy servers is to act as storage or cache for web pages that are frequently accessed by devices on the internal network. For example, the proxy server in the figure is storing the web pages for www.cisco.com. When any internal host sends an HTTP GET request to www.cisco.com, the proxy server completes the following steps: 1. It intercepts the requests. 2. It checks to see if the website content has changed. 3. If not, the proxy server responds to host with the web page. In addition, a proxy server can effectively hide the IP addresses of internal hosts because all requests going out to the internet are sourced from the proxy server's IP address.

RFID

RFID uses the frequencies within the 125 MHz to 960 MHz range to uniquely identify items, such as in a shipping department. Active RFID tags that contain a battery can broadcast their ID up to 100 meters. Passive RFID tags rely on the RFID reader to use radio waves to activate and read the tag. Passive RFID tags are typically used for close scanning but have a range of up to 25 meters.

Repeater

Regenerating weak signals is the primary purpose of a repeater. Repeaters are also called extenders because they extend the distance a signal can travel. In today's networks, repeaters are most often used to regenerate signals in fiber-optic cables. Also, every networking device that receives and sends data regenerates the signal.

Routers

Routers can have all the functionality of a switch or a wireless AP. However, routers connect networks, as shown in the figure. Switches use MAC addresses to forward traffic within a single network. Routers use IP addresses to forward traffic to other networks. In larger networks, routers connect to switches, which then connect to LANs, like the router on the right in the figure. The router serves as the gateway to outside networks. also known as a multipurpose device or integrated router. It includes a switch and a wireless access point. For some networks, it is more convenient to purchase and configure one device that serves all your needs than to purchase a separate device for each function. This is especially true for the home or small office. Multipurpose devices may also include a modem for connecting to the internet.

Switches

Switch Operation Every device on a network has a unique media access control (MAC) address. This address is hardcoded by the manufacturer of the NIC. As devices send data, switches enter the device's MAC address into a switching table that records the MAC address for each device connected to the switch, and records which switch port can be used to reach a device with a given MAC address. When traffic arrives that is destined for a particular MAC address, the switch uses the switching table to determine which port to use to reach the MAC address. The traffic is forwarded out the port to the destination. By sending traffic out of only one port to the destination, other ports are not affected. Managed and Unmanaged Switches In larger networks, network administrators typically install managed switches. Managed switches come with additional features that the network administrator can configure to improve the functionality and security of the network. For example, a managed switch can be configured with VLANs and port security. In a home or small business network, you probably do not need the added complexity and expense of a managed switch. Instead, you might consider installing an unmanaged switch. These switches typically have no management interface. You simply plug them into the network and attach network devices to benefit from a switch microsegmentation features.

File Transfer Server

The File Transfer Protocol (FTP) provides the ability to transfer files between a client and a server. An FTP client is an application that runs on a computer that is used to push and pull files from a server running FTP as a service. As the figure illustrates, to successfully transfer files, FTP requires two connections between the client and the server, one for commands and replies, the other for the actual file transfer. FTP has many security weaknesses. Therefore, a more secure file transfer services should be used, such as one of the following: File Transfer Protocol Secure (FTPS) - An FTP client can request the file transfer session be encrypted. The file server can accept or deny the request. SSH File Transfer Protocol (SFTP) - As an extension to Secure Shell (SSH) protocol, SFTP can be used to establish a secure file transfer session. Secure Copy (SCP) - SCP also uses SSH to secure file transfers.

WLAN Protocols

The Institute of Electrical and Electronic Engineers' (IEEE) standards for Wi-Fi as specified in the 802.11 collective group of standards that specify the radio frequencies, speeds, and other capabilities for WLANs. Various implementations of the IEEE 802.11 standards have been developed over the years The 802.11a, 802.11b, and 802.11g standards should be considered legacy. New WLANs should implement 802.11ac devices. Existing WLAN implementations should upgrade to 802.11ac when purchasing new devices. IEEE Standard: 802.11a, Maximum Speed: 54 Mb/s, Maximum Indoor Range: 115 ft (35 m), Frequency: 5 Ghz, Backwards Compatible: None. IEEE Standard: 802.11b, Maximum Speed: 11 Mb/s, Maximum Indoor Range: 115 ft (35 m), Frequency: 2.4 Ghz, Backwards Compatible: None. IEEE Standard: 802.11g, Maximum Speed: 54 Mb/s, Maximum Indoor Range: 125 ft (38 m), Frequency: 2.4 Ghz, Backwards Compatible: 802.11b. IEEE Standard: 802.11n, Maximum Speed: 600 Mb/s, Maximum Indoor Range: 230 ft (70 m), Frequency: 2.4 Ghz and 5 Ghz, Backwards Compatible: 802.11a/b/g. IEEE Standard: 802.11ac, Maximum Speed: 1.3 Gb/s (1300 Mb/s), Maximum Indoor Range: 115 ft (35 m), Frequency: 5 Ghz, Backwards Compatible: 802.11a/n.

Host Devices

The network devices that people are most familiar with are called end devices or host devices (Figure 1). They are called end devices because they are at the end or edge of a network. They are also called host devices because they typically host network applications, such as web browsers and email clients, that use the network to provide services to the user.

Web Server

Web resources are provided by a web server. The host accesses the web resources using the Hypertext Transfer Protocol (HTTP) or the secure HTTP (HTTPS). HTTP is a set of rules for exchanging text, graphic images, sound, and video on the World Wide Web. HTTPS adds encryption and authentication services using Secure Sockets Layer (SSL) protocol or the newer Transport Layer Security (TLS) protocol. HTTP operates on port 80. HTTPS operates on port 443. To better understand how the web browser and web server interact, we can examine how a web page is opened in a browser. For this example, use the http://www.cisco.com/index.html URL. First, the browser interprets the three parts of the URL: 1. http (the protocol or scheme) 2. www.cisco.com (the server name) 3. index.html (the specific filename requested) The browser then checks with a Domain Name Server (DNS) to convert www.cisco.com into a numeric address, which it uses to connect to the server. Using HTTP requirements, the browser sends a GET request to the server and asks for the index.html file. The server sends the HTML code for this web page back to the client's browser. Finally, the browser interprets the HTML code and formats the page for the browser window.

Wireless Access Points

Wireless access points (APs), shown in the figure, provide network access to wireless devices, such as laptops and tablets. The wireless AP uses radio waves to communicate with the wireless NIC in the devices and other wireless access points. An access point has a limited range of coverage. Large networks require several access points to provide adequate wireless coverage. A wireless access point provides connectivity only to the network, while a wireless router provides additional features.

Z-Wave

Z-Wave technology is a proprietary standard that is now owned by Silicon Labs. However, a public version of the interoperability layer of Z-Wave was open sourced in 2016. These open source Z-Wave standards include Z-Wave's S2 security, Z/IP for transporting Z-Wave signals over IP networks, and Z-Ware middleware. Z-Wave operates within a variety of frequencies based on the country from 865.2 MHz in India to 922 - 926 MHz in Japan. Z-Wave operates at 908.42 MHz in the North America. Z-Wave can transmit data up to 100 meters but has a slower data rate than Zigbee at 9.6-100 kb/s. Z-Wave can support up to 232 devices in one wireless mesh network.

ZigBee

Zigbee uses low-power digital radios based on the IEEE 802.15.4 wireless standard for low-rate wireless personal area networks (LR-WPANs) that is meant to be used by low-cost, low-speed devices. Zigbee operates within frequencies from 868 MHz to 2.4 GHz and is limited to 10 to 20 meters. Zigbee has a data rate from 40-250 kb/s and can support approximately 65,000 devices. The ZigBee specification relies on a main device called a ZigBee Coordinator. Tasked with managing all ZigBee client devices, the ZigBee Coordinator is responsible for the creation and maintenance of the ZigBee network. Although Zigbee is an open standard, software developers must be a paid member of the Zigbee Alliance to use and contribute to the standard.

Land Area Network (LAN)

a network that encompasses a small geographical area. However, the distinguishing characteristic for LANs today is that they are typically owned by an individual, such as in a home or small business, or wholly managed by an IT department, such as in a school or corporation

TCP/IP Model

consists of layers that perform functions necessary to prepare data for transmission over a network. TCP/IP stands for two important protocols in the model: Transmission Control Protocol (TCP) and Internet Protocol (IP). TCP is responsible for tracking all the network connections between a user's device and multiple destinations. The Internet Protocol (IP) is responsible for adding addressing so that data can be routed to the intended destination. two protocols that operate at the transport layer are TCP and User Datagram Protocol (UDP) TCP is considered a reliable, full-featured transport layer protocol, which ensures that all of the data arrives at the destination. In contrast, UDP is a very simple transport layer protocol that does not provide for any reliability TCP transport is analogous to sending packages that are tracked from source to destination. If a shipping order is broken up into several packages, a customer can check online to see the order of the delivery. With TCP, there are three basic operations of reliability: Numbering and tracking data segments transmitted to a specific device from a specific application Acknowledging received data Retransmitting any unacknowledged data after a certain period of time UDP is similar to placing a regular, non-registered, letter in the mail. The sender of the letter is not aware of the availability of the receiver to receive the letter. Nor is the post office responsible for tracking the letter or informing the sender if the letter does not arrive at the final destination. UDP provides the basic functions for delivering data segments between the appropriate applications, with very little overhead and data checking. UDP is known as a best-effort delivery protocol. In the context of networking, best-effort delivery is referred to as unreliable because there is no acknowledgment that the data is received at the destination.

wireless mesh network (WMN)

networks using multiple Wi-Fi access points to create a wide area network that can be quite large and are essentially a series of interconnected local area networks. uses multiple access points(AP) to extend the WLAN