L12 - Consultation (Summary of the NEF Lectures) R4 (1).pdf

Network Engineering Fundamentals (CSE2&5NFE) Lecture 12 - Consultations Summary of the NEF Lectures Textbook reference: CISCO: Network Fundamentals, CCNA Exploration Companion Guid, 2008 Edition Chapters 1 to 11 1(20) Ne...

Network Engineering Fundamentals (CSE2&5NFE) Lecture 12 - Consultations Summary of the NEF Lectures Textbook reference: CISCO: Network Fundamentals, CCNA Exploration Companion Guid, 2008 Edition Chapters 1 to 11 1(20) Network is a group of people or machines that use a set of common communication protocols for the purpose of sharing information that are located on or provided by the network members (the people or the machines). Humans are part or users of many public networks: Professional networks (Engineers Association, Medical Association) Social networks (Religious, Sports, Political, Internet based (Facebook, Tweeter…)) Broadcast networks (Radio, TV, Internet streaming) Telecommunication networks (Voice/Telephony, Data (email, Internet)) Telecommunication data networks based on TCP/IP suite can be public and private. An example of public network is Internet which is freely accessible by the users. Private data TCP/IP networks can be classified as: ▪ Intranets - Are private networks in use by just one company, they enable businesses to communicate and perform transactions among global employee and branch locations. ▪ Extranets (Extended Internetworks) - Are used by companies to provide the suppliers and customers limited access to corporate data to check order status, inventory, and parts lists. 2(20) The term Network Architecture refers to the conceptual plans on which a physical network is built. Networks’ architecture design needs to address the following four requirements: Fault Tolerance – enables a network to function normally even when some of the components of the network fail. Scalability – enables to expand to support new users, new equipment and connect to new external networks. Quality of Service (QoS) - refers to the mechanisms that manage congested network traffic. Security - is essential when Internet is used the for financial, government and businesses transactions. Networks as a Communication Platforms have the following common elements: Messages - are units of information that travel from one device to another. Devices - Laptops, PCs, servers, LAN switches, router, smartphones etc. A device can operate as an End Device or as an Intermediate Device. Media or Medium - Cables used to connect the devices, equipment for wireless connection etc. Rules or agreements (protocols) - govern how the messages are sent, directed, received, and interpreted. The rules can be seen as: o Services - are the software programs that provide information in response to a request (e-mail services, web services); these are the Applications. o Processes - are the software programs that provide the functionality that directs and moves the messages through the network; these are the Protocols. 3(20) The IT and Telecom industries use layered models to describe the complex process of a network communication, where the functions in the specific process are grouped into well defined layers. The OSI (Open Systems Interconnection ) model is a REFERENCE MODEL, it TCP/IP is an open standard, developed by the provides an abstract description of the IETF (Internet Engineering Task Force). network communication process. TCP/IP is the base of the Internet. Applications used by 7. Application the end users. Provides data format 6. Presentation Application information to the application. Manages sessions between 5. Session users. 4. Transport Transfers and receives application Transport data to and from the destinations. Routes the data packets 3. Network Network through the networks. Creates data frames for delivery 2. Data Link between directly connected devices. Network access 1. Physical Transmits binary data over media between directly connected devices. 4(20)  The following are the most widely known TCP/IP Application Layer Protocols: Domain Name System (DNS) is used to resolve Internet names to IP addresses. Hypertext Transfer Protocol (HTTP) is used to transfer files that make up the web pages of the World Wide Web. Simple Mail Transfer Protocol (SMTP) is used for the transfer of mail messages and attachments. Telnet, a terminal emulation protocol, is used to provide remote access to servers and networking devices. File Transfer Protocol (FTP) is used for interactive file transfer between systems. The protocols in the TCP/IP suite are generally defined by Requests for Comments (RFC). The Internet Engineering Task Force (IETF) maintains the RFCs as the standards for the TCP/IP suite. To exchange information the applications use one or more of the following Network Data Exchange Modes: Client/Server mode - the device requesting the information is called a client and the device responding to the request is called a server. Peer-to-Peer mode, which can have two forms: o Peer-to-Peer network - two or more computers are connected through a network and every device can function as either a server or a client (file sharing applications). The roles of client and server are set on a per-request basis. Peer-to-Peer applications - the devices act simultaneously as both a client and a server within the same communication session (voice over IP, instant messaging). In this model, every client is a server and every server a client. 5(20) E-Mail Processes The e-mail client uses the Mail Transfer Agent (MTA) application to send and receive e-mails. The e-mail server operates two separate processes: Mail Transfer Agent (MTA) - to receive e-mails from a client MUA and forward e-mails to a server MTA. Mail Delivery Agent (MDA) - to accept e-mails from a local or remote Mail Transfer Agent (MTA) and to perform the e-mail delivery by placing the e-mails into the users’ mailboxes. The most common application layer protocols for E-mail services are: Post Office Protocol (POP)/Internet Message Access Protocol (IMAP); and Simple Mail Transfer Protocol (SMTP). POP and IMAP are used to deliver e-mail from the e-mail server, using the Mail Delivery Agent (MDA) application, to the e-mail client, which uses the Mail User Agent (MUA) application to receive the e-mail. SMTP is used to send e-mails from the sending e-mail client using the MUA application to the e-mail server which uses the Mail Transfer Agent (MTA) application to receive e-mail. SMTP is also used to transfer e-mails between two e-mail servers; the Mail Transfer Agent (MTA) application is 6(20) used to send and receive the e-mail.  Transport Layer performs segmentation of long application data (splits the long block of data in smaller blocks). Transport layer supports several protocols to meet the requirements of different applications. The two most common transport layer protocols of the TCP/IP protocol suite are: ▪ TCP (Transmission Control Protocol) ▪ UDP (User Datagram Protocol). TCP is used by applications whose data is not sensitive to delays and do not tolerate loss of data. TCP uses the following function to achieve that: Maintaining connection sessions - Before a host sends data to another host, TCP initiates creates (both way) connection session with the remote destination. Flow control and remote host load control - Receiving end provides indication in the “window” parameter how much data can receive without acknowledging the sent data. Network congestion control - Sending end maintains transmission restriction parameter “congestion window” which is dynamically adjusted based on the frequency of retransmitted segments. Retransmission of lost data - Sending end retransmit lost and corrupted data which are indicated by the receiving end. UDP is a simple, connectionless protocol, that provides the basic functions for delivering the data between the applications. It supports application identification and error detection but there is no loss recovery, congestion control and flow control. Thus, UDP has the advantage of providing low-overhead data delivery. The data packets in UDP are called datagrams. 7(20) Port Number parameters (source and destination) are included in the TCP and UDP headers and are used to uniquely identify the applications at each end of the conversation. Internet Assigned Numbers Authority (IANA) assigns port numbers. IANA is also a standards body that is responsible for assigning various addressing standards. The different types of port numbers are: Well-known ports (numbers 0 to 1023) – used for “well known” (server and client) applications or processes. Registered ports (numbers 1024 to 49151) – used for user (client) processes or applications. Dynamic or private ports (numbers 49152 to 65535) - ), also known as ephemeral (transient) ports, are usually assigned dynamically to client applications when initiating a connection. Port Numbers assignment method is dependant on the type of application process at the hosts: Server processes are assigned with static (“well known”) port numbers. Client processes may use dynamically assigned port numbers for each conversation (the selected number must not be used by an other client process on the host). Client software must know the destination port number of the server process on the remote server host. Destination port number in the client software is configured either by default or manually. Example When a web browser application makes a request to a web server, the browser uses destination port number 80 in the TCP header, which is the default port assigned to web-serving applications. Many other common applications are assigned with default port numbers. 8(20) Chapter 5 presents the functionalities of OSI Network Layer, Layer 3, though the functionalities of the widely used Internet Protocol version 4 (IPv4). IPv4 basic characteristics are: Connectionless - IPv4 does not establish a connection before sending data packets. Best effort (unreliable) - IPv4 does not use processes that guarantee packet delivery. Media independent - IPv4 operates over different media: wireless, Ethernet cable and fiber-optic cable media. The IP header holds the delivery and handling instructions for an IP packet, these are: Version: Indicates IP version 4 or 6. IHL (Internet Header Length): Indicates how long the header is.. Type of Service (ToS): Forwarding priority of the packet; also known as QoS or quality of service. Total Length: This is the total length of the datagram, including the header. Identification: Sent by the source to help reassemble any fragments. Flags and Fragment Offset: Used to reconstruct a fragmented packet when it arrives at the destination host. Time to Live (TTL): Maximum hops the packet can take before it is considered “lost” or undeliverable. Protocol: Indicates the transport layer protocol, for example, TCP, UDP, or ICMP. Header Checksum: Used for error protection of the header content only. Source Address: 32-bit binary value that represents the host that sends the packet.. Destination Address: 32-bit binary value that represents the host that will receive the packet. Options: A rarely used field that can provide special routing services. Padding: Padding is used to fill in bits when header data does not end on a 32-bit boundary. 9(20) Route is a path to a network i.e., Route is an interface (channel) towards a destination network. The information about the routes are stored in the Routing Table. Destination network can be : A connected network is directly attached to one of a router interface. A remote network is a networks that is not directly connected to the router. Routing Table contains the main information about the Routes, these are: Destination network IP address Metric Next-hop [router IP address and interface] Routing is the process performed when forwarding packets, it involves analysing the destination address information and the characteristics of the available paths before selecting a path for forwarding the packet. Hop is the route that a packet takes to reach the next device. A packet can hop between several different routers before it reaches to the destination. Large computer networks can be separated/restructured into smaller networks. Historically, large computer networks were divided geographically, because workers with common tasks tended to be clustered into workgroups. Today network members can be grouped not just by physical (size, geography) attributes, but also by abstract attributes such as purpose and ownership. 10(20) IPv4 address is 32 bits parameter where the 32 bits are grouped in two parts: Network Portion; and Host Portion. The number of bits in the network and host portions can vary. Subnet Mask is a 32-bit parameter which is used to define the number of bits in the Network and the Host Portions. Subnet Mask is created by placing a binary 1 in each bit position that represents a network bit of the address and placing a binary 0 in the remaining bit positions that represent the host portion of the address. The number of Host Portion bits determines the size of the addressing block required for a network: 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝐼𝑃 𝑎𝑑𝑑𝑟𝑒𝑠𝑠𝑒𝑠 = 2𝑁𝑢𝑛𝑏𝑒𝑟 𝑜𝑓 𝐻𝑜𝑠𝑡 𝑝𝑜𝑟𝑡𝑖𝑜𝑛 𝑏𝑖𝑡𝑠 Network Prefix or Prefix Length is used as short representation of the address mask, it indicates the number of bits used to identify the network portion of the address. Prefix Length is written in “slash” format: a forward slash (/) followed by the number of network bits. For example, in the notation “192.168.8.20 /24”, the first part is the IP address (192.168.8.20) and the second part (/24) is the prefix length, which indicates that the first 24 bits are the network portion of the address and the remaining 8 bits are the host portion of the address. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 1 0 0 0 0 0 0|1 0 1 0 1 0 0 0|0 0 0 0 1 0 0 0|0 0 0 1 0 1 0 0| => 192.168.8.20 /24 -----+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IP address Network | prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |1 1 1 1 1 1 1 1|1 1 1 1 1 1 1 1|1 1 1 1 1 1 1 1|0 0 0 0 0 0 0 0| => 255.255.255.0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Subnet Mask | \----------------------------------------------/ \--------------/ | Network Portion = 24 bits