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DCN : Section 7

DCN : Section 7. Internet Technology. Learning Objectives. Introduction to Internet and classful IP addressing Internet and Intranet; Understand of subnet and subnet mask; Understand the relationship between domain name and DNS;

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DCN : Section 7

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  1. DCN : Section 7 Internet Technology

  2. Learning Objectives • Introduction to Internet and classful IP addressing • Internet and Intranet; • Understand of subnet and subnet mask; • Understand the relationship between domain name and DNS; • Introduction to the components of Intranet; such as web servers, routers and proxy service; • Familiar with with TCP/IP protocol suite; • Introduction to security issues, such as cryptography, PKI and CA, etc.

  3. Internet (1) • The Internet is • A network of networks. • Connecting networks from homes, schools, and businesses worldwide. • A decentralized, global collection of networks using TCP/IP suite protocols for communication. • The Internet (capital I) refers to a specific WAN made up of many interconnected networks around the globe, including servers and routers.

  4. Internet (2) • The Internet provides the following: • A global collection of text files, multimedia files, etc. • A collection of network services interconnected by a system of hypertext documents. • Web browsers to access WWW • Hypertext documents formatted in HTML supported by Internet WWW servers.

  5. Internet (3)

  6. Internet Addressing

  7. Internet Scaling Problems (1) • IP version 4 (IPv4) addressing mechanism for addressing packets and directing information on a network. • The current IPv4 defines 2^32 (4,294,967,296) addresses available. • IP addressing shortage has caused the following: • Continuing depletion of IP v4 address space; • Difficulty in routing traffic between more networks on the Internet Super Highway.

  8. Internet Scaling Problems (2) • The address shortage problem is aggravated by the fact that portions of the IP addresses have not been efficiently allocated due to the significant amount of organizations have their own IP addresses. • Also, the traditional model of classful addressing does not allow the address space to be used to its maximum potential. • The long term solution to these problems can be deployed IPv6.

  9. Classful IP Addressing (1) • A unique IP address for each network • The 32 bits are divided into network number and host number. • Two-level Address Structure • The network number (also called network-prefix) identifies the network on which the host resides. • The host number identifies the particular host on the given network.

  10. Classful IP Addressing (2) • All hosts on a given network share the same network number, but have a unique host number. • Any two hosts on different networks may possess different network number, but may have the same host number.

  11. Classful IP Addressing (3) • Developed to support different size of networks. It is decided that the IP address space should be divided into classes. • Addressing scheme of each class specifies a boundary between the network number and the host number at a different point within the 32-bit address. • Connecting the private network to the Internet, however, requires using a registered IP address to avoid duplicates.

  12. Classful IP Addressing (4) • To prevent duplication, an organisation called Internet Information Center (InterNIC) assigns Internet addresses to organizations and individuals that requires an Internet site. • IP address space was divided primarily into • Class A: for network with more than 216 hosts • Class B: for network with between 28 and 216 hosts • Class C: for network with fewer than 28 hosts

  13. Classful IP Addressing (5) • The host calculation requires that 2 is subtracted because of the all 0s (“this network”) and all 1s (“broadcast”) host numbers cannot be assigned to individual hosts.

  14. Class A Networks (/8 Prefixes) • Each Class A (/8) network address has a 8-bit network -prefix with the highest order bit is set to zero and a 7-bit network number, followed by 24-bit host number. • A maximum of 126 (2^7-2) /8 networks can be defined. • The calculation requires that the 2 is subtracted because the /8 network 0.0.0.0 is reserved for use as the default route and /8 network 127.0.0.0 (also written 127.0.0.0/8) has been reserved.

  15. Class A Networks (/8 Prefixes) • Each /8 supports a maximum of 16,777,214 (2^24-2) hosts per network. • Since the /8 address block contains 2^31 (2,147,483,648) individual addresses and the IPv4 address space a max of 2^32 (4,294,967,296) addresses, the /8 address space is 50% of the total address space.

  16. Class B Networks (/16 Prefixes) • Each Class B (/16) network address has a 16-bit network-prefix, with the two highest order bits set to 1-0, and a 14-bit network number, followed by a 16-bit host number. • A maximum of 16,384 (2^14) /16 networks can be defined with up to 65,534 (2^16-2) hosts per network. • Since the entire /16 address block containing 2^30 (1,073,741,824) addresses, it represents 25% of the total IPv4 address space.

  17. Class C Networks (/24 Prefixes) • Each Class C (/24) network address has a 24-bit network-prefix, with the three highest order bits set to 1-1-0, and a 21-bit network number, followed by a 8-bit host number. • A maximum of 2,097,152 (2^21) /24 networks can be defined with up to 254 (2^8-2) hosts per network. • Since the entire /24 address block containing 2^29 (536,870,912) addresses, it represents 12.5% of the total IPv4 address space.

  18. Other Classes • There are two additional classes – Class D and E. • Class D addresses have their leading four bits set to 1-1-1-0. It is used to Support IP multicasting. • Class E addresses have their leading four bits set to 1-1-1-1. It is used for research and experimental purposes

  19. Dotted Decimal Notation (1) • To make Internet address easier for human users to read and write, it can be expressed as 4 decimal numbers, each separated by a dot. This is called dotted decimal notation. • It divides the 32-bit Internet address into four 8-bit (byte) fields and specifies the value of each field.

  20. Dotted Decimal Notation (2) • /8 (A) – 1.xxx.xxx.xxx through 126.xxx.xxx.xxx • /16 (B) – 128.0.xxx.xxx through 191.255.xxx.xxx • /24(C) – 192.0.0.xxx through 223.255.255.xxx • xxx represents the host number field, which is assigned by the local network administrator. • Note that: 127.xxx.xxx.xxx has been reserved for looping test purpose.

  21. Problems of two-level classical hierarchy(1) • The present two-level classical hierarchy faces the problem of • Global routing tables were beginning to grow very fast. • Local administrators had to request another network before a new network could be installed at their own site. • Subnetting, which supports three-level hierarchy, was introduced. • It increases addressing capacity. • It divides private network into smaller components, called subnets.

  22. Problems of two-level classical hierarchy (2)

  23. Subnets (1) • Based on a three-level hierarchy: a network number, a subnet number, and a host number created from the bits allocated for your host number. • Subnetting attacked the expanding routing table problem by ensuring that the subnet structure is NEVER visible outside of the organization’s private network. (ie Subnet number of a network is not advertised to external networks).

  24. Subnets (2) • It routes from a public network to any subnet of an IP address is the same, regardless of the subnet on which the destination host resides. • It is used the same network number but different subnet numbers. • Routers in private network must differentiate between each subnet. • All of the subnets in the organisation are collected into a single routing table entry.

  25. Subnets (3) • Router is set to accept all traffic from the Internet to your designated IP address (for example, 132.132.0.0). • Traffic is received and forwarded to the interior subnets you have set up (for example, 132.132.32.0, 132.132.64.0, 132.132.96.0, 132.132.128.0 and ...., which are using 3-bit in the third octet of the IP as subnets).

  26. Subnets (4) • Internet routers use only the network-prefix of the destination address for routing traffic to a subnet configuration. • Routers use the extended network-prefix to route traffic between subnets. • Extended network prefix consists of the class network prefix and the subnet number. • Extended network prefix is identified by a subnet mask.

  27. Using Subnet Masks (1) • If you are given a network address: 132.132.0.0/16, the default subnet mask for /16 (class B) is to be 255.255.0.0. • The host ID can be ranged from 132.132.0.1 to 132.132.255.254. • A total of 2^16-2 (65534) hosts can be placed to this network. ( network-prefix) ( host ) 132.132.0.0/16 = 10000100.10000100. 00000000. 00000000 subnet mask = 10000100.10000100. 00000000. 00000000

  28. Using Subnet Masks (2) • You are also given a network address: 132.132.0.0/16 and want to use the first 3 bits of third octet to represent the subnet number. • Since 8=23, three bits are required to achieve eight subnets. • This network is subnetting a /16 so it will need three more bits, or /19, as the extended network-prefix. • A 19-bit extended network-prefix can be expressed in 255.255.224.0.

  29. Using Subnet Masks (3) • The eight subnet numbers are given below. The 19-bit extended network-prefix has been shown italics. subnet #0 = 10000100.10000100. 00000000. 00000000 = 132.132.0.0/19 subnet #1 =10000100.10000100. 00100000. 00000000 = 132.132.32.0/19 subnet #2 =10000100.10000100. 01000000. 00000000 = 132.132.64.0/19 subnet #3 =10000100.10000100. 01100000. 00000000 = 132.132.96.0/19 subnet #4= 10000100.10000100. 10000000. 00000000 subnet #5= 10000100.10000100. 10100000. 00000000 subnet #6= 10000100.10000100. 11000000. 00000000 subnet #7= 10000100.10000100. 11100000. 00000000

  30. Using Subnet Masks (4) subnet #4 =10000100.10000100. 10000000. 00000000 = 132.132.128.0/19 subnet #5 =10000100.10000100. 10100000. 00000000 = 132.132.160.0/19 subnet #6 =10000100.10000100. 11000000. 00000000 = 132.132.192.0/19 subnet #7= 10000100.10000100. 11100000. 00000000 = 132.132.224.0/19

  31. Using Subnet Masks (5) • An easy way to check if the subnets are correct is to ensure they are multiples of the subnet#1 address. In this case, they are of multiples of 32: 0, 32, 64, 96, 128, …. • The lowest and highest number of subnet will not be used. In fact, there are only SIX possible subnets in the above case. • In general, • Possible subnets = 2 (number of masked bits) - 2 • Possible hosts per subnet = 2 (number of masked bits) - 2

  32. Using Subnet Masks (6) • After two examples, we have done the following: • Set the subnet mask bits to 1 if your network treats the corresponding bit in the IP address as part of the extended network prefix • Set the subnet mask bits to 0 if your network treats the bit as part of the host number. • The internal network address is the logical AND of the subnet mask with the IP address. • The host number within the subnet is the remaining host address portion of the IP address.

  33. DNS (1) • Because IP addresses are hard to remember, the text version of the IP address is always used. This text version is called a domain name. • For example, the IP address 198.105.232.4 would be translated to microsoft.com • To translate and track domain names, InterNIC uses the Domain Name Service (DNS).

  34. DNS (2) • DNS is a set of distributed databases containing IP addresses and their corresponding domain names. • DNS, with servers located all over the Internet, performs the translation back and forth between names and numbers. • A user can type in a domain name instead of the IP address.

  35. DNS (3)

  36. Domain Name (1) • DNS uses several levels of naming conventions, each of which is called a domain. • A domain refers to a group of computers and devices on a network that is administered as a unit with common rules and procedures. • Top-Level Domain (TLD): it indicates the class of institution, such as .com, .edu, .gov, .org • Second-Level Domain (SLD): it is registered by an organisation or entity by InterNIC, such as ibm, microsoft

  37. Domain Name (2)

  38. Domain Name (3)

  39. World Wide Web (1) • The collection of hyperlinked documents accessible on the Internet is known as the World Wide Web, WWW, W3 or simply Web. • A Web site is where a related collection of web pages or files stored on a web server. • Web Browser: a client program which requests a web page from a web server and displays it on the local computer

  40. World Wide Web (2) • Uniform resource locator (URL): it is the address of a file accessible on the WWW, such as an HTML web pages or any file supported by the HTTP.

  41. Intranet • It is used to be an internal corporate network enhanced with Internet technology, such as adopting a WWW browser, email and newsgroup system. • It emphasizes in secured against inappropriate access, such as password control. • So that, it is often connected to outside Internet via a firewall and/or a router for protecting any intruder’s attack.

  42. Web Server • Application that publishes HTML and other types of documents on the World Wide Web. • It receives an HTTP, FTP, or other type of request for a document from a browser, it responds by sending the document to the browser. • A secure web server is a server on the WWW that supports one or more of the major security protocols such as Secure Socket Layer (SSL) or HTTPS.

  43. Firewall • A firewall sets an electronic boundary that prevents unauthorized users from accessing certain location on a network • It can examine each packet in the stream to see whether if the sender is authorized access • It is designed to control the flow of packets based on the source, destination, port and packet type information in each packet • It can be implemented in hardware, software, or a combination of both.

  44. Router • A router is a device that connects two or more networks. • It sorts addressed data packets and sends them to the correct destinations with the built-in routing table. • It can connect networks that use different network adapters or transmission media as long as both sides of connection use same protocols.

  45. Proxy Server • It is used to overcome delays, slower response times, and security concerns. • Traffic problems are partly due to the repeated retrieving of objects from remote Web servers. • Caching frequently requested Internet information. • It reduces the number of times the same information is accessed over an Internet connection, the download time, and the load on the remote server.

  46. Proxy Service Benefits (1) • It reduces WAN traffic to the Internet and on the primary Web server by providing local LAN access to cached information. • It reduces the load on Web Internet servers and increases Internet and intranet performance. • It enhances intranet security with access control and content filtering, which can avoid users to indecent web sites.

  47. Proxy Services Benefits (2) • It distributes LAN client requests across multiple proxy servers, for example, FTP requests on one server and HTTP requests on another server. • Proxy servers receive your requests, check for authorization, then go to get information. If you are not authorized, your request will be denied. • ISPs can use proxy servers to stop users from going to certain sites, too.

  48. OSI Model versus TCP/IP

  49. TCP/IP Suite of Protocols (1) • TCP/IP is the Internet suites of network protocols that allows different computers to communicate. • Underneath TCP/IP, there are various media protocols that help move the data over the various networks on the Internet. • TCP/IP also works in conjunction with the following protocols for specific applications.

  50. TCP/IP Suite of Protocols (2) • FTP (File Transfer Protocol) for file transfer • HTTP (HyperText Transfer Protocol) for browsing in WWW • HTTPS (http with Secure Socket Layer) for secure data transfer in WWW • NNTP (Network News Transfer Protocol) for news group reading • SMTP (Simple Mail Transfer Protocol) for delivering e-mail

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