PROG1225-07 Lecture-Networking Introduction.pdf

1225 Unit Seven: Networking Introduction Overview When two computers communicate using a local network (like a home network) or the Internet, communication happens at three levels – hardware, operating system, and application. The three basic steps in networking communication are:    1st: one c...

1225 Unit Seven: Networking Introduction Overview When two computers communicate using a local network (like a home network) or the Internet, communication happens at three levels – hardware, operating system, and application. The three basic steps in networking communication are:    1st: one computer must find the other. 2nd: both computers must agree on the methods and rules for communication – called protocols. 3rd: one computer takes on the role of making request from the other computer – in a client/server model (like a web browser and web server) – or both computers make requests from each other – in a peer-to-peer model (like two computers on a home network sharing files). Network Communication Layers When two devices communicate, they must use the same protocols so that the communication makes sense. For almost all networks today, including the Internet, the group or suite of protocols used is called TCP/IP (Transmission Control Protocol/Internet Protocol). In the above example, communication starts with an application (browser) passing a request to the OS, which passes the request to the network card and then on to the network. When the request reaches the network card on the server, the network card passes it on to the OS and then the OS passes it on to the application (the web server).  Hardware Level: consists of some type of network card and connection to the network. o Network connection – can be wireless (like Wi-Fi, satellite, cellular) or use some type of cabling (like Ethernet cables, phone lines, coaxial cables).4  Wi-Fi (IEEE 802.11) and Ethernet are the most common types of connections for home and offices. o Network Adapter (or Network Card, Network Interface Card, NIC) – includes any network connector (port) or wireless access circuitry.  MAC (Media Access Control) Address (or Hardware Address, Physical Address, Adapter Address) – Every network adapter has a 48-bit (6 byte) hexadecimal number hard-coded on the card by its manufacturer that is unique for that device. Part of the MAC address identifies the manufacturer of the network adapter.    MAC addresses are used to locate a computer on a local area network (LAN). A LAN is a group of computers and devices (like printers and storage devices) connected together in the same general location (like a house or building). Operating System Level: use IP (Internet Protocol) addresses to find other computers on a network. o IP Address – a 32-bit or 128-bit number that is assigned to a network device (like a computer or printer) when a connection is first made.  MAC addresses are used only to find computers on a local network and is also used when assigning IP addresses – a certain MAC address can be given a specific IP address or can even be banned from getting an IP address.  IP addresses are used to find computers on the Internet as well as local networks that use the TCP/IP protocol. Intranets are local networks that use the TCP/IP protocols. IP addresses can be helpful in locating a computer when a local network has been divided into smaller networks called a subnetwork or subnet. Application Level: use port numbers to determine which application is requesting information from the Internet. o Port Number (Port or Port Address) – a preassigned number that uniquely identifies the type of application on the computer. A web browser will typically use port 80 and an email program will typically ‘listen’ for incoming email at port 25. The port number is usually added to the end of a IP address. Before a message is transmitted on a network, if it is too long, it’s broken up into smaller pieces. Header and trailer information is added, including the IP addresses of the source and destination computer, and the application’s port number. When this information is added, the message (or message pieces) is called a segment, datagram, packet, or frame depending on what information has been added to the header and trailer and which layer of communication added the information. OSI Protocol Layers vs TCP/IP OSI (Open Systems Interconnection) Reference Model: is a seven-layer communication model developed to categorize the layers of communication – developed by the International Organization for Standardization (ISO). Layer 1: Physical Layer  Responsible only for sending bits via a wired or wireless transmission. Layer 2: Data Link Layer (or just Link Layer)    Responsible for interfacing with the physical hardware only on the local network. Ethernet and Wi-Fi are the typical link layer protocols used which is programmed into all the hardware on the local network. The Ethernet and Wi-Fi protocol uses the MAC address for transmitting data. The information coming from this layer is called a Frame. Layer 3: Network Layer     Responsible for moving messages from one node to another until they reach the destination host. IP (Internet Protocol) is the main protocol used at this layer which uses IP addresses to identify nodes (devices) on a network. The information coming from this layer is called a Packet. IP relies on several routing protocols to find the best route for a packet when traversing several networks on its way to its destination. These routing protocols include ICMP (Internet Control Message Protocol) and ARP (Address Resolution Protocol). Layer 4: Transport Layer  Responsible for transporting application layer payloads (data) from one application to another on different computers.    TCP (Transmission Control Protocol) makes a connection with the end host, checks whether the data is received, and resends it if it is not. TCP is sometimes called a connection-oriented protocol. TCP is used by applications such as Web browsers and email. Guaranteed delivery takes longer and is used when it is important to know that the data reached its destination. UDP (User Datagram Protocol) does not guarantee delivery by checking whether data is received – so UDP is sometimes called a connectionless protocol or best-effort protocol. UDP is used for broadcasting, such as streaming video or audio over the Web, where guaranteed delivery is not as important as fast transmission. USP is also used to monitor network traffic. The information coming from this layer is called either a segment (TCP) or datagram (UDP). Layer 5: Session Layer  Describes how data between applications is synced and recovered if messages don’t arrive intact at the receiving application. Layer 6: Presentation Layer  Responsible for reformatting, compressing, and/or encrypting data in a way that the application on the receiving end can read. Layer 7: Application Layer    Describes the interface between two applications, each on separate computers. HTTP, SMTP, POP3, IMAP4, FTP, Telnet, and RDP are examples of TCP/IP application layer protocols. The information coming from this layer is called a payload and includes control information like the port number of the application (which is based on the application layer protocol used). The Application, Presentation, and Session layers are so intertwined that it is often difficult to distinguish between them. Tasks for each layer may be performed by the operating system or the application. Most tasks are performed by the OS when an application makes an API (Application Programming Interface) call to the OS – which is a method an application uses when it makes a request of the OS. Below is a table relating the different layers with each model… OSI Model Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Protocols and Services HTTP, SMTP, POP3, IMAP4, FTP, Telnet, RDP (TCP/IP suite of protocols embedded in the OS) TCP or UDP IP, ICMP, and ARP Ethernet TCP/IP Model Basic 3 Layer Model Applications (Web Browser, Email) Application Layer Application Layer Operating System Layer Transport Layer Network Layer Network Interface Layer Hardware Layer As noted above, each TCP/IP layer adds data to be transmitted (when data is added it’s called encapsulation and when data is removed it’s called decapsulation) …     Application Layer – payload data Transport Layer – adds a header to the payload data to create a segment (TCP) or datagram (UDP) Network Layer – adds another header to the segment/datagram to create a packet Network Interface Layer – adds another header and a trailer to a packet to create a frame TCP/IP Protocols Common protocols used by networking applications include:              HTTP (Hypertext Transfer Protocol) (Port #80): used for the World Wide Web and used by web browsers and web servers to communicate. HTTPS (HTTP Secure) (Port #443): refers to the HTTP protocol working with a security protocol such as Secure Sockets Layer (SSL) or Transport Layer Security (TLS) to create a secured (encrypted) socket – a connection between a browser and web server. SMTP (Simple Mail Transfer Protocol) (Port #25): used to send an email message to its destination. POP (Post Office Protocol) (Port #110) or IMAP (Internet Message Access Protocol) (Port #143): used to download messages from an email server. POP3 (POP version 3) or IMAP4 (IMAP version 4) is used. Telnet (Port #23): an unsecured protocol used to connect to another computer. LDAP (Lightweight Directory Access Protocol) (Port #389): used by various client applications when querying a database. LDAP is not encrypted – LDAPS (LDAP Secure) (Port #636) is encrypted. SMB2 (Server Message Block version 2) (Port #445): can be used to share files and printers on a network. Also called CIFS (Common Internet File System). FTP (File Transfer Protocol) (Port #20 & #21): used to transfer files between two computers. FTP by default is not encrypted – SFTP (Secure FTP) uses SSH encryption (Port #22). SSH (Secure Shell) (Port #22): protocol encrypts transmission so they cannot be intercepted. SSH is commonly used in Linux to pass sign-in information to a remote computer and control that computer over a network. SNMP (Simple Network Management Protocol) (Port #161 and #162): used to monitor network traffic. RDP (Remote Desktop Protocol) (Port #3389): used by the Windows Remote Desktop and Remote Assistance utilities to connect to and control a remote computer. DNS (Domain Name Server) (Port #53): used to resolve a computer name (or web address) to an IP address. DHCP (Dynamic Host Configuration Protocol) (DHCPv4: Port #67 & #68) (DHCPv6: Port #546 & #547): used to assign an IP address to a network device. IP Addresses IP address are the backbone of network communication:     Static IP: an IP address that doesn’t change. Dynamic IP: an IP address that does change – typically received by a DHCP server. IPv4 (IP version 4) uses a 32-bit IP address in 4 groups of 8 bits each – usually seen in decimal number system o Addresses range from 0.0.0.0 (currently unassigned IP address) to 255.255.255.255 (used by broadcast messages by TCP/IP background processes). o 127.0.0.1 indicates your own computer and is called the loopback address. o Private IP addresses are not allowed on the Internet and are used for private internal networks:  10.0.0.0 to 10.255.255.255 (16,777,216 IP addresses)  172.16.0.0 to 172.31.255.255 (1,048,576 IP addresses)  192.168.0.0 to 192.168.255.255 (65,536 IP addresses) o IPv4 addresses use subnet masks to identify which part of an IP address is the network portion and which part is the host portion (the part of the address that identifies the individual devices on the network). o APIPA (Automatic Private IP Address): if no DHCP server is available and no static IP is currently assigned then the computer can assign its own IP address in the range from 169.254.0.0 to 169.254.255.255. IPv6 (IP version 6) uses a 128-bit IP address in 8 groups of 16 bits each – usually seen in hexadecimal number system o Example: 2001:0000:0b80:0000:0000:00d3:9c5a:00cc (in hex) … leading zeros in a four-character hex block can be eliminated: 2001:0000:b80:0000:0000:d3:9c5a:cc … if blocks contain all zeros, they can be written as double o o o o colons: 2001:0000:0b80::d3:9c5a:cc … only one set of double colons can be used in an IP address else ambiguity can occur – so pick the longest run of zeros. Here are a few terms used in the IPv6 standards:  A link, sometimes called the local link, is any local area network (LAN) bounded by routers (hardware devices used to connect computers and networks together and directs traffic between them).  An interface is a node’s (networking device) attachment to a link (either wired or wireless).  The last 64 bits (or four blocks) of an IPv6 address identify the interface and are called the interface ID or interface identifier. These 64 bits uniquely identify an interface on the local link (or in English: The last four blocks uniquely identify a device on the local network).  Neighbors are two or more nodes on the same link. IPv6 classifies IP addresses differently than IPv4. IPv6 supports these three types of IP addresses, classified as to how the address is used:  Unicast address – this type of address specifies a single node on a network. Three types of unicast addresses are global, link local, and unique local addresses.  Multicast address – packets are delivered to all nodes in the targeted, multicast group.  Anycast address – this type of address can identify multiple destinations, with packets delivered to the closet destination. Example: A DNS name server might send a DNS request to a group of DNS servers that have all been assigned the same anycast address. A router handling the request examines routes to all the DNS servers in the group and routes the request to the closest server.  IPv4 uses broadcasting which sends messages to every node on a network. IPv6 reduces network traffic by eliminating broadcasting. Three types of unicast addresses:  Global addresses – also called a global unicast address, can be routed on the Internet.  Link local addresses – also called a link local unicast address or local address, can be used for communicating with nodes in the same link (LAN).  Unique local addresses – is a private address that can travel across subnets within the private network. These addresses are used by network administrators when subnetting a large network. IPv6 uses subnetting but doesn’t need a subnet mask because the subnet ID that identifies a subnet is part of the IPv6 address.  The subnet ID is the 16 bits following the first 48 bits of the address (used by either global addresses or unique local addresses). The following table shows the address prefixes for types of IPv6 addresses: IPv6 Address Type Link-local Address Unique local Address Global Address Multicast Unassigned Address Loopback Address Address Prefix fe80::/64 fc00::/7 2000::/3 ff00::/8 0::0 0::1 or ::1 Notes First 64-bits are always fe80:0000:0000:0000 (in hex) First 7-bits are always 1111 110 (or fc in hex) First 3-bits are always 001 First 8-bits are always 1111 1111 (or ff in hex) All 64-bits are zeros First 127 bits are zero, the last bit is one (0:0:0:0:0:0:0:1 in hex) Character Based Names Remembering an IP address in not always easy, so character-based names are used to substitute for IP addresses.    Host Name, also called a computer name, is the name of a computer and can be used in place of its IP address. A workgroup is a group of computers on a peer-to-peer network that are sharing resources. The workgroup name assigned is only recognized within the local network. A domain name identifies a network (like microsoft.com or google.com).  A fully qualified domain name (FQDN) identifies a computer and the network to which it belongs. Example: www.microsoft.com – the host name is www (a web server), Microsoft is the domain name, and com is the top level domain. Whereas msdn.microsoft.com identifies another computer – msdn. On the Internet, a fully qualified domain name must be associated with an IP address before a particular computer can be found. This process of associating a character-based name with an IP address if called name resolution.  DNS (Domain Name System or Domain Name Service) protocol is used by a DNS server to find an IP address for a computer when the fully qualified domain name is known. o Home Internet Service Providers (ISPs) are responsible for providing access to one or more DNS servers as part of the service it provides for Internet access. o When a computer tries to resolve a computer name to an IP address, it first looks in the DNS cache stored in memory – if not found, it then uses a DNS server for which it has an IP address for. o DNS Client is a device requesting DNS services.