Introduction to Networking IT 112 PDF

Introduction to Networking 1 IT 112 2 Networking Basics  Key terms  Network Interface  Network Cable  Wall Jack  Local Area Network (LAN) 3  Wide Area Network (WAN)  Metropolitan Area Network (MAN)  Bus Topology  Ring Topology  Star Topolo...

Introduction to Networking 1 IT 112 2 Networking Basics  Key terms  Network Interface  Network Cable  Wall Jack  Local Area Network (LAN) 3  Wide Area Network (WAN)  Metropolitan Area Network (MAN)  Bus Topology  Ring Topology  Star Topology  Mesh Topology  Key terms  Physical Address  Logical Address  Default Address Class  Internet Protocol (IP) 4  Modem  Router  Switch  Access Point  Firewall  Home Router  Key terms  Registered Jack 11 (RJ-11) Interface  Registered Jack 45 (RJ-45) Interface  Bluetooth  Near Field Communications (NFC) 5  Connecting to a network 6 ◼ A network is group of computer systems that are interconnected to share information with each other ◼ The information must be turned into small bits (packets) which may be sent via different paths and must be reassembled at the destination in the correct order. ◼ Network clients and computers and software that allow users to request resources shared by and hosted on servers.  Connecting to a network 7 Network media must be used to connect the computers. This is usually done with copper wiring or radio signals. A network interface must be installed in each computer to connect it to the network media. Network protocols must be configured on each computer. The same protocol must be configured on all computers in the network for them to communicate with each other. 8 Wired Network Components The network interface provides an RJ-45 port into which a network cable can be connected. On desktop computers, this port is usually found on the back. On notebooks and laptops, it is usually found on the side of the system. The wall jack has an RJ-45 port that provides a connection to the wired network. It appears similar to a telephone wall jack but is larger in size. The network cabling connects the computer to the wired network. One end of the cable connects to the RJ-45 port on the computer. The other end connects to the RJ-45 port in the wall jack. 9 Wired Network Components  Network Cable: A cable that provides connectivity between network devices. A common network cable connects a computer's network interface with a wall jack.  Coaxial Cable: A cable that provides transmission on a network through its inner wire in the form of electrical signals. The wire is made up of four different components: an inner conductor, an insulator made of flexible PVC, a metallic shield, and a plastic jacket coating.  Twisted Pair Cable: A cable that transmits data through electrical signals and provides better signals because of its unique eight plastic-coated copper wires that are twisted into four pairs. 10 11  Fastest medium Very inexpensive Immune to EMI Inflexible Very long cable Can’t install lengths connectors 12  Wireless Internet Services 13  While a cabled Internet Service will usually offer the best bandwidth, they are not always available.  Wireless services can be used in areas where it is too difficult or expensive to lay cable.  Microwave Satellite  Cellular radio  GSM (Global System for Mobile Communication)  TIA/EIA IS-95 (CDMA)  Long Term Evolution (LTE)  LTE advanced (LTE-A)  Radio Frequency 14 Wireless Networking Connection  Some networks use radio signals to communicate instead of copper wiring. They are called wireless networks. The process for connecting to a wireless network is a little more complex, To connect to a wireless network, a computer must have a wireless network interface available. Different platforms have different types of wireless options available. On desktop systems, you must typically install a wireless network interface. The easiest way to do this is to insert a USB wireless network interface into an available USB port. Most notebook and laptop systems provide an integrated wireless network interface, so you do not need to install one. However, you may need to switch it on. Most notebook and laptop systems provide a button or switch that enables or disables the wireless network interface  Types of Wireless Hardware 15 There are three types of wireless adapters currently available:  Add-on cards using the PCI (Peripheral Component Interconnect) or PCIe (PCI Express) standards for desktop computers.  USB (Universal Serial Bus) adapters for use with USB 2.0 or 3.x ports.  Internal adapters in laptop or tablet computers; laptop wireless adapters can sometimes be replaced or upgraded. 16 Network Categories Local Area Network A LAN is a group of connected computers that are physically close, usually (LAN) in the same building. The computers in your office, school, or library are probably connected to each other on a LAN. Wide Area Network WANs are networks of interconnected LANs across a large geographical (WAN) location. A WAN can cover a city, a state, a country, or even the entire world. Private A private network can be accessed only by computers inside the network. This is essential for businesses that want employees to have access to the files they need for work and want to provide a high level of data protection. Public Public networks can be accessed freely by anybody. The most important public network is the worldwide system of interconnected networks called the internet.  Local Area Network (LAN)  a network of connected devices localized in a single physical location, such as in a single office building, private residence.  LANs can connect devices by Ethernet cables (a wired connection) or over Wi-Fi (a wireless connection). 17 18 LAN Benefits Devices can share a single Internet connection Devices can print to shared printers Devices can share files with one another Devices can access or control each other if needed  Wide Area Network (WAN)  WAN stands for wide area network, which means that it's made up of a larger geographical area than a LAN. In fact, it connects multiple LANs to create a much larger network.  For example, if you have a company that has a headquarters and branch offices spread across different cities, each branch will have its own LAN, and all these company LANs will be connected into the larger WAN.  A router is usually used to make the connection between a LAN and a WAN, but sometimes dedicated telecommunication lines are used as well.  the Internet itself is simply a very large WAN that connects thousands of LANs all over the world. 19 20 Metropolitan Area Network (MAN)  Is a kind of network that covers a larger geographical area than a LAN, but isn't usually as large as a WAN.  Large cities such as London and New york have created MANs, but large universities also refer to their networks as MANs due to their size and complexity. 21 Network Composition/Area Feature type LAN Fewer devices Share files Limited geographical area Share printers Share control of devices MAN Many devices Similar to a LAN Larger geographical area such as a city or campus WAN Connected LANs Uses VPNs Very large geographical area Share applications Share firewalls 22 Device addresses  For a computer to send or receive information on a network, it needs a network address.  You can think of a network address in the same way as a mailing address. A mailing address needs to include a state, city, street, and house number.  Network addresses work similarly in that they have different parts. Each part lets other devices know where information goes. Network addresses, like mailing addresses, must be unique. No two devices on the same network can have the same network address.  Physical address ✓ The physical address of a device is also called the media access control (MAC) address. MAC addresses are burned into the read-only memory of every network interface, such as wireless network adapters and network interface cards. This makes it virtually impossible to change the device's MAC address. ✓ An important feature of MAC addresses is that they are globally unique. No two network interfaces in the world have the same MAC address. An example of a MAC address is 00-09-5B-36-C2-93. The MAC address is sometimes shown as a group of four hex values (e.g.,0009.5B36.C293). Public ✓ Logical addresses are assigned by software and, as such, can be changed. They include two parts: the network address and the host address. o The network address specifies the network segment (also called a subnet). o All devices on the same network segment share the same logical network address. o The logical host address identifies a specific host on the network. Each device must have a unique logical host address. ✓ The most common types of logical addresses are those assigned by the IP protocol and are called IP addresses. IP addresses combine the logical network and logical host addresses into a single address. An example IP address is: 192.168.1.1 23 24 25 IP Addresses ✓ In a small network with a few computers, a printer, and a server, each device would have its own IP address. The format for an IP address is four numbers between 0 and 255, separated by periods (e.g., 192.168.1.1). ✓ This is known as a dotted decimal notation. Each segment of the address is called an octet. This is because in binary, each section is represented by eight digits, from eight zeros all the way up to eight ones, which is the same as 255 in decimal. Is a 32-bit binary number represented as four octets (four 8-bit numbers). Each octet is separated by a period. Can be represented in one of two ways: Decimal (e.g., 131.107.2.200). In decimal notation, each octet must be between 0 and 255. Binary (e.g., 10000011.01101011.00000010.11001000). In binary notation, each octet is an 8-digit number.  Includes both the network address and the host address. Uses a subnet mask to differentiate the network and host address 26 27 IP Address Classes Class Address Range Subnet Mask A 1.0.0.0 255.0.0.0  IP addresses use default classes 126.255.255.255 that include a default subnet mask value. The class defines the default B 128.0.0.0 255.255.0.0 network address portion of the IP 191.255.255.255 address. C 192.0.0.0 255.255.255.0 223.255.255.255 D 224.0.0.0 N/A 239.255.255.255 E 240.0.0.0 N/A 255.255.255.255 28 IP Version 6  IP version 4 works great, with one small problem: as more devices have connected to the internet, all available IP addresses have been used.  To solve this problem, the internet is transitioning into a new format called IP version 6.  IPv6 addresses are expressed as 32-character hex numbers. IPv4 has about four billion potential addresses. IPv6 has trillions (340 undecillion, a number equal to 1 followed by 36 zeros). 29 Networking Devices - Modem  Modem is short for modulator/demodulator. Signals that arrive at your network from an Internet Service Provider (ISP), whether through fiber, cable, or phone line, can't be directly understood by your computer.  Instead, the signal passes through a modem that translates it into a series of electrical ones and zeros that travel through a copper wire to your computer. To upload data to the internet, the modem does the opposite, turning ones and zeros into light, cable, or phone signals 30 Router  A router's job is to send signals from one network to another. When you send an email, the signal travels through a wire or radio signal to your network's router. The router sees that data is addressed to a different network and forwards it to the ISP.  The ISP's router looks at the data, sees where it's supposed to go, and sends it to the router on the network where the recipient's mail server is stored. 31 Switch Similar to the way a router transfers data between networks, switches transfer data between devices within a network. Every computer on the network is connected to the switch. Whenever a computer sends a signal or a signal comes in from the router, the switch looks at the data. If it recognizes the receiving computer as another device on the switch, it sends it directly to that computer. If it doesn't recognize the data, it sends it to the router. A switch in a Small Office Home Office (SOHO) usually has anywhere from four to eight RJ-45 ports. A switch in the enterprise environment has 20 or more ports. Switches in the enterprise environment can be interconnected. This allows them to provide support for hundreds of connections. 32 Access point  Conceptually, an access point (AP) works in a similar way to a switch; it recognizes the device that should receive the signal, then forwards the data to where it needs to go. The main difference is that APs use Wi-Fi technology to connect devices to the network wirelessly; a switch uses wires. In an enterprise network, the AP supports more devices than those used in a SOHO. 33 Firewall  As amazing as the internet is, it's full of malicious people and software that you want to keep away from your computer. A firewall checks each bit of data (called a packet) that tries to enter your network. If the firewall decides the packet is safe, it passes it along. Otherwise, it drops or rejects the packet. This firewall function is called packet filtering 34 Home router  For a small network, most people buy a single router. These are usually called wireless (Wi-Fi) routers.  Home router is small network device with modem, firewall, routing, and switching features that is used in homes and small businesses. 35 Networking Interfaces  RJ-11 : The Registered Jack 11 interface (RJ-11) has four pins and a clip to hold the plug into a wall socket. RJ-11 is used to connect to a telephone line. In a DSL network, this interface connects the modem to the wall jack.  RJ-45 : The RJ-45 interface is much more common in today's networks. These jacks have eight pins and are a little wider than RJ-11 connectors.  Bluetooth: Bluetooth is a technology used to create wireless connections between computers and devices. Bluetooth uses radio signals to connect devices at a short range, usually no more than ten meters. 36 Networking Interfaces  RFID : RFID, can be used for tracking objects. There are two types of RFID, passive (does not require power) and active (does require power). Passive RFID tags can be embedded in labels and stickers for tracking in manufacturing and shipping.  Fixed infrastructure RFID readers can scan data up to 100 feet  Commons uses is placing RFID labels on products to prevent theft.  Near Field Communications (NFC) : A technology that uses specially encoded tags that respond in a specific way when scanned by a radio frequency reader. NFC is often used by placing a smartphone near a scanner to pay for an item in a store. 37 Virtual LAN (VLAN)  A virtual LAN (VLAN) is a logical grouping of computers based on a switch port.  Most screened segments, also known as demilitarized zones (DMZs), are created using a VLAN. You can configure multiple VLANs with varying security requirements on one switch. This keeps the cost down.  Things to consider when setting up a VLAN:  VLAN membership is configured by assigning a switch port to a VLAN.  A switch can have multiple VLANs configured on it, but each switch port can be a member of only one VLAN. The one exception is described below. 38 Virtual LAN (VLAN)  Network media refers to the communication channels used to interconnect nodes on a computer network.  Typical examples of network media include copper coaxial cable, copper twisted pair cables and optical fiber cables used in wired networks, and radio waves used in wireless data communications networks. 39 Screened Subnet ( demilitarized zone )  Is a segmented network (or subnet) that sits between the private network and an untrusted network, such as the internet. Typically: Firewalls allow traffic that originates in the secured internal network into the screened subnet and through to the internet. Traffic that originates in the screened subnet (low-security area) or the internet (no-security area) should not be allowed access to the intranet (high-security area). 40 Client - Server Model servers provide network services to the clients on the network. Now, instead of storing files on Bob's computer, users can store them on the server. They can also use the server to manage the printer. Even if their computers are turned off, they'll still have access to the network services on the server.  Connecting to a network 41  Networks of Many Sizes  Small Home / Office Networks  Medium to Large Networks  World Wide Network  Clients and Servers  Clients request and display information  Servers provide information to other devices on the network  Peer-to-Peer  Computers can be both server and client at the same time. 42 Class discussion  What hardware components are needed for a wired network? A wireless network? 43 Key Definitions  Attenuation: A feature of radio waves where the signal becomes weaker as the wave travels further from its point of origin. 802.11 standards require that signals are strong enough to cover a specific distance.  Speed: A characteristic of 802.11 protocols that require them to transfer data at a specific number of bits per second.  Bluetooth: A technology used to create wireless connections between computers and devices.  Wi- Fi: A technology that uses radio signals to connect a device to an access point. 44 Ethernet Ethernet 45  Wireless Internet Services 46  While a cabled Internet Service will usually offer the best bandwidth, they are not always available.  Wireless services can be used in areas where it is too difficult or expensive to lay cable.  Microwave Satellite  Cellular radio  GSM (Global System for Mobile Communication)  TIA/EIA IS-95 (CDMA)  Long Term Evolution (LTE)  LTE advanced (LTE-A)  Radio Frequency  Types of encryption in a Wi-Fi network 47  There are three different types of encryption you can use with a Wi-Fi network: WEP, WPA, WPA2.  Wired Equivalent Privacy (WEP) was the first type of wireless security developed.  WEP is flawed and you would only select this if compatibility with legacy devices and software is imperative.  Wi-Fi Protected Access (WPA): WPA uses the same weak RC4 (Rivest Cipher) cipher as WEP but adds a mechanism called the Temporal Key Integrity Protocol (TKIP) to make it stronger.  WPA2: It uses AES (Advanced Encryption Standard) cipher for encryption. AES is much stronger than RC4/TKIP  Speed Limitations 48 There are a couple of factors that affect Wi-Fi speeds such as:  The greater the distance between an access point/wireless router and a wireless client, the slower the speed of the connection.  When wireless devices that support different speeds connect, they connect at the speed of the slower device.  When network channel congestion is present with 2.4GHz wireless networks, a single 20MHz channel may be used on 802.11n-compatible wireless access points even though 802.11n supports wilder channels.  The more data streams connecting devices, the better the performance.  Interference & Attenuation Factors 49  Interference: Interference is caused by devices that are operating in the same frequency as the wireless network.  For example, devices that can interfere with 2.4GHz networking include some types of cordless phones, some wireless mice and keyboards, early versions of Bluetooth, and some types of home automation devices.  Attenuation: It is the loss of signal strength in networking cables or connections.  It is measured in decibels (dB).  It may cause signals to become indiscernible. An example of this is Wi-Fi signal and strength getting noticeably weaker the further that your device is from the router. In wireless transmission, attenuation could be caused by objects in the path of the signal, such as doors, walls, or trees. Wireless Standards 50 Wireless Standards 51 Wireless Standards 52 53 Internet Connectivity  Key Terms  Digital Subscriber Line (DSL)  Satellite  Cellular 54  Wi-Fi  Virtual Private Networks (VPN) 55 Key Definitions  Dial Up: A technology used in the early days of the internet where a computer would make a phone call to the ISP to establish internet connectivity.  Digital Subscriber Line (DSL): A technology that uses phone lines to establish high-speed connectivity to the internet through an ISP. 56 Key Definitions Satellite: A technology that sends signals to and from a satellite to establish connectivity to the internet through an ISP. Cellular: A technology that uses cellular radio signals to establish connectivity to the internet. Wi- Fi: A technology that uses radio signals to connect a device to an access point. Virtual Private Network (VPN): A tool that allows internet users more security and privacy using a public internet connection to create a private network that shields the user's data from others. A VPN masks a user's IP address to make their actions untraceable. 57 Key Definitions  Wi- Fi: A technology that uses radio signals to connect a device to an access point.  Virtual Private Networks (VPN): A tool that allows internet users more security and privacy using a public internet connection to create a private network that shields the user's data from others. A VPN masks a user's IP address to make their actions untraceable. 58 Internet Service Types 59 Cable Modem  Cable Internet is generally provided by the same company that sends cable TV signals to your house.  Since cable companies can already send multiple TV channels on the same cable, they can easily add a few extra channels for data. Just like with dial up, cable connections require a modem to convert analog cable signals into digital computer signals. Satellite 60 Internet Service Types 61 62 Wi-Fi  Uses radio signals to connect a cell phone to a smaller network  Data can be downloaded to your phone 63 Networking protocols  Key Terms  Internet Protocol (IP)  Transmission Control Protocol (TCP)  User Datagram Protocol (UDP)  Domain Name System (DNS) 64  Hypertext Transfer Protocol (HTTP)  Hypertext Transfer Protocol Secure (HTTPS)  Key Terms  Simple Mail Transfer Protocol (SMTP)  Post Office Protocol 3 (POP3)  Internet Message Access Protocol (IMAP)  HTTP Method 65  Dynamic Host Configuration Protocol (DHCP)  Subnetting  Subnet Mask 66 Key Definitions  Internet Protocol (IP): The principal communications protocol in the internet protocol suite that is used to route information over the Internet.  Transmission Control Protocol (TCP): An important protocol in the internet protocol suite that enables two hosts to establish a connection and exchange data.  User Datagram Protocol (UDP): An important protocol in the internet protocol suite that is generally used when speed in transmission is more important than accuracy since the sending computer doesn't verify that the packets were correctly received. 67 Key Definitions  Domain Name System (DNS): A protocol that helps internet users and network devices discover other devices using a human-readable hostname instead of numeric IP addresses.  Hypertext Transfer Protocol (HTTP): A protocol that governs the transfer of web content between computers.  Hypertext Transfer Protocol Secure (HTTPS): A protocol that combines HTTP with the Secure Sockets Layer (SSL) protocol to securely transfer web content between computers. 68 Key Definitions  Simple Mail Transfer Protocol (SMTP): A protocol used to send email.  Post Office Protocol 3 (POP3): A protocol used to receive email. With POP3, email is deleted from a server after it is downloaded to a client.  Internet Message Access Protocol (IMAP): A protocol used to receive email. With IMAP, email is saved on a server even after it is downloaded to a client. 69 Key Definitions  HTTP Method: A command that tells the server what the user wants to do. The most common methods are POST, GET, PATCH, and DELETE. These methods are used for CRUD operations which stand for Create, Read, Update, and Delete.  Dynamic Host Configuration Protocol (DHCP): A network management protocol that assigns IP addresses on a network. It is part of the larger set of built-in networking protocols known as TCP/IP. 70 Key Definitions  Subnetting: Dividing a network into smaller subnets.  Subnet Mask: A value given to an address in a subnetted network that tells a computer which numbers are part of the network or subnet address and which are part of the host address. 71 72 TCP/IP  To help understand the functions of a networking system a conceptual framework known as the Open Systems Interconnection Mode (OSI Model) is used. This model is a theoretical way of classifying and talking about the complex process of sending data on a network.  However, to better understand how TCP/IP functions, there is also a TCP/IP model.  The TCP/IP model focuses specifically on the functions in the Internet layer and the Transport layer. All other functions of the traditional OSI model are encompassed in the first and fourth layers 73 Application Layer  The Application layer contains high-level protocols used by processes (applications) running on a host for network communications. The Application layer integrates network functionality into the host operating system and enables network services. The Application layer does not include specific applications that provide services, but rather provides the capability for services to operate on the network. 74 Transport Layer The Transport layer is responsible for error checking and reliable delivery. In the transport layer, each application protocol is identified by a port number. Protocols that are associated with the Transport layer include: Transport Control Protocol (TCP) - Adds a header to each IP packet. The TCP header helps the receiving computer to assemble the packets into the correct configuration once the entire file is downloaded. The headers also allow the sending and receiving computers to verify with each other that each packet was received correctly. User Datagram Protocol (UDP) - Is generally used when speed in transmission is more important than accuracy, such as streaming audio or video. Like TCP, UDP adds a header to each packet. However, unlike TCP, the sending computer doesn't verify that the packets were correctly received. This makes transmissions happen much faster but allows transmission errors. 75 Internet Layer  The Internet layer is responsible for forwarding packets through multiple networks. This process is called routing and is done by encapsulating the packets into internet datagrams. The Internet layer manages host addressing and routing decisions to identify how packets traverse networks.  Protocols that reside at the Internet layer include. Internet Protocol (IP) - the IP protocol uses logically-assigned IP addresses to uniquely identify networks and network hosts. This helps in the routing of the packets between each host and network. Address Resolution Protocol (ARP) - This protocol links an IP address to a host's physicals address (MAC address). For example, when you use a browser to access a site, you use the IP address (a number not too difficult to remember or use). However, to communicate with the host, the process needs to know the MAC address (hardware address) found on the interface card or device. ARP discovers the MAC address for you. Internet Control Message Protocol (ICMP) - It's main job is to send error messages and other operational information to let the systems know if the data was transferred successfully or if there was an error during transmission. It is used by network devices, including routers. Internet Group Management Protocol (IGMP) - This protocol is used by hosts and adjacent routers to establish multicast group memberships. IGMP is an integral part of IP multicast and allows the network to direct multicast transmissions only to hosts that have requested them. 76 Link Layer  The Link layer is responsible for describing the physical layout of the network and how messages are electrically transmitted. It is used to move information between hosts by controlling how individual bits are transmitted and received on the network medium.  The Link layer converts the data to be transmitted into frames by adding a Link layer header that includes physical device addressing information. Each frame processed by the Link layer includes the source MAC address and the destination MAC address. The Link layer then converts the frames into bits for transmission across the network media. Internet Protocols 77 Internet Protocols 78 79 Internet Protocols  DNS (Domain Name System) 80  The domain name system (DNS) is the phonebook of the internet. Humans access information online through domain names, like Facebook.com or YouTube.com.  Web browsers interact through internet protocol (IP) addresses.  DNS translates domain names to IP addresses so browsers can load internet resources. DNS works by translating a URL into the actual IP address used by that resource.  The DNS is the name for the network of servers on the internet that translates domain names, such as www.google.com, and individual hostnames into their matching IP addresses. If you manually configure an IP address, you typically provide the IP addresses of one or more DNS servers as part of the configuration process.  DNS uses port 53.  HTTP and HTTPS 81 ◼ Hyper text Transfer Protocol (HTTP) is the basis of the World wide web. ◼ Is is usually used to serve HTML web pages, which are plain text files with coded tags. ◼ A web browser can interpret the tags and display the text and other resources associated with the page, such as pictures or sound files. ◼ HTTP enables clients (typically web browsers) to request resources from an HTTP server. ◼ A client connects to the HTTP server using its TCP port (the default port is 80) and submits a request for a resource using a Uniform Resources Locator (URL). ◼ The server acknowledges the request and returns the data. ◼ Hypertext Transfer Protocol Secure (HTTPS) - Provides secure transfer over the internet. One of the biggest downsides of HTTP is that it transmits data as plain text. An attacker could intercept the signal during transmission and read the sensitive information it contains. When websites need to send or receive data securely, they use HTTPS, which combines HTTP with the Secure Sockets Layer (SSL) protocol. SSL encrypts data so unauthorized parties can't understand the data even if they manage to intercept it. Internet Protocols 82  SSL/ TLS 83 ◼ Secure Socket Layer (SSL) is an encryption technology used by secured (https://) websites. ◼ To access a secured website, the web browser must support the same encryption level used by the secured website (normally 128-bit encryption) and the same version(s) of SSL used by the website (normally SSL version 2.0 or 3.0). ◼ Sites secured with SSL display a padlock beside the browser’s URL and often a green address bar if secured by a certificate. ◼ Https operates over port 443 by default. ◼ Transport Layer Security (TLS) is the successor to SSL. SSL3 was somewhat of a prototype to TLS and was not fully standardized. ◼ TLS was ratified by the IETF in 1999. However, many people and companies might still refer to it as SSL.  Email Protocols and services 84  SMTP 85 ◼ SMTP: Simple Mail Transfer Protocol (SMTP) is a protocol for sending email messages between servers. ◼ Most email systems that send email over the internet use SMTP to send messages from one server to another; the messages can then be retrieved with an email client using either POP or IMAP. ◼ In addition, SMTP is generally used to send messages from a mail client to a mail server. SMTP uses TCP port 25. ◼ When configuring email settings on a client, you need to know the server type(s) used (SMTP, POP3, or IMAP), the ports used (default values may be changed by some ISPs), the username and password for the email service, and the security settings.  POP3 86 ◼ POP3 (Post Office Protocol 3), is the third version of a widespread method of receiving email. Similar to the physical version of a post office clerk, POP3 receives and holds email for an individual until they pick it up. ◼ All versions of POP work by checking an email server and downloading new messages to your email client app. ◼ For users who have only one computer, POP3 works well. However, for users who switch between computers, POP3 and earlier versions have a major limitation. ◼ If you retrieve email on a desktop computer and on a laptop, each computer will have only some of the messages unless you configure your email server to keep a copy of your email. When the server keeps a copy of downloaded email, you might download the same messages over and over again. ◼ POP3 uses TCP port 110.  IMAP 87  Internet Message Access Protocol (IMAP) is an internet standard protocol used by email clients to retrieve email messages from a mail server over a TCP/IP connection.  Instead of downloading new messages to the user’s computer, IMAP displays messages when received and enables the user to keep them on the server and organize them in folders.  If a user checks for email using IMAP on multiple devices, all devices can show all of the user’s email. A user can delete IMAP messages whenever necessary.  Multiple users can check a single email box at the same time. When configuring a new email service, the user must select the protocol to use.  IMAP4 is the current version of IMAP. IMAP uses TCP port 143. 88 Subnetting Subnetting 89 Subnetting 90 Subnetting 91 Subnetting 92 Subnetting 93 94 Class Discussion  When might it be better to use TCP? When might it be better to use UDP?  Why is it important for computers to use communications protocols?  What is the relationship between subnet masks, IP addresses, and the binary number system? 95 Questions ?