Chapter 12: Internetworking and the Internet

1. Chapter 12:Internetworking and the Internet Principles of Computer Networks and Communications M. Barry Dumas and Morris Schwartz

2. Objectives • Define and explain internetworks and intranets • Describe the Internet’s topology and explain why its structure might be described as pseudo-hierarchical • Discuss the beginnings of the World Wide Web, its evolution and its relation to the Internet • Describe Internet networking with the client/server model • Explain the composition of URLs and examine addressing issues • Discuss issues associated with IPv4 addressing and the move from IPv4 to IPv6 Principles of Computer Networks and Communications

3. Overview • Internetwork: a group of autonomous networks • Company internets and intranets typically revolve around LANs • When varying locations are involved, use WANs • Hierarchies help organize provider access • The issue of names and addresses on the Internet is complex • Classful vs. Classless addressing • The IPv4 system will soon be out of addresses • A move to IPv6 system is necessary When these networks use TCP/IP protocols, they’re called extranets Principles of Computer Networks and Communications

4. Overview • Company internet • Company-owned network, typically revolves around the LAN • Uses LAN protocols (e.g., ethernet, token-ring, etc.) • Designed only to be reached by authorized employees • Company intranet • Company-owned, in-house network • Uses TCP/IP protocols • Designed only to be reached by authorized employees • Company extranet • Company-owned, special outsider access to in-house network • Uses TCP/IP protocols • Connects between the owner company and networks of “participating organizations” (e.g., suppliers, outsourcers, etc.) Principles of Computer Networks and Communications

5. History of the Internet Revisited • Usually traced back to its precursor, the ARPANET project • Main concern—interconnecting independent (mainframe) computers • Later concern—the development of a robust internetwork • That could keep military communications flowing • That could deal with complicated communications with incompatible networks • Can be linked to the Advanced Research Projects Agency (ARPA) • The U.S. response to the 1957 USSR launch of the Sputnik Principles of Computer Networks and Communications

6. “The topology of the Internet . . . is a pseudo-hierarchical structure based on links among different levels of service providers.” Internet Topology and Access • Serviceproviders • Organizations whose nodes and links supply all of the interconnections • Order of main hierarchy • International Internet service providers (IISPs) and national service providers (NSPs) at the top • Most NSPs are also IISPs • Regional service providers (RSPs) • Local Internet service providers (ISPs) at the bottom Many providers connect directly to each other, whether at the same or different levels Local providers offer dial-up access, bringing the telephone system into the picture Principles of Computer Networks and Communications

7. Internet Topology and Access • National service providers (NSPs) • Form the Internet backbone that extends worldwide • Are private companies that own and maintain the backbone networks • Basic global interconnections are provided by NSPs linked to each other through network access points (NAPs) • NAPs are complex switching stations • NAPs are privately owned, usually by companies other than NSPs • Some NSPs bypass NAPs to link directly to each other using peering points in their switching offices Peering points are like the POPsof telephone companies’ end offices Principles of Computer Networks and Communications

8. Internet Topology and Access • Regional service providers (RSPs) • Through routers • Connect hierarchically to NSPs • Connect directly to other RSPs • Local Internet service providers (ISPs) • Can link to NSPs, RSPs, and ISPs • The higher up on the hierarchy, the faster the links and the greater their capacity • ISPs can support many connection types • Dial-up, cable modem, DSL, ATM, frame relay, Ethernet • Not all ISPs can support all types Most individuals and businesses use ISPs to connect Principles of Computer Networks and Communications

9. Basic Topology of the Internet Some RSPs connect directly to each other by routers NSPs are linked to each other by NAPs Some NSPs connect directly to each other by peering points Fig. 12.1 Principles of Computer Networks and Communications

10. Internet2 and Abilene • Internet2 • Nonprofit development project • Academic, industry, government partnership • Led by more than 200 universities • Purpose—to create advanced technologies and applications that can be adopted by the Internet • Will eventually lead to the “Internet of the future” • Formation and constituency are reminiscent of predecessors • Abilene • High-speed wide-bandwidth optical backbone network • Designed to support Internet2 Abilene participants:—Indiana University—Juniper Networks—Nortel Networks—Qwest Communications in partnership with Internet2 Principles of Computer Networks and Communications

11. Hyperlinks are addresses that take us from page to page and site to site, and make traversing the Internet straightforward The World Wide Web aka “the Web” • An interface that allows us to access the Internet • Tim Berners-Lee in 1990 • Wrote the first World Wide Web server: httpd • Created “WorldWideWeb” • the first client • a hypertext browser/editor • Web browser software • Simplified the information-finding process on the Internet providing easy-to-use Web interfaces • Websites • Collections of files (pages) organized by links • Via a structure called hypertext (that contains hyperlinks) Web interfaces:Microsoft Internet ExplorerNetscape NavigatorMozilla Firefox Principles of Computer Networks and Communications

12. The Client/Server Model • Name refers to the association between network entities • Client software requests services • Server software provides services • A software model, not a hardware model • Because it is software based, the client/server model provides a flexible and scalable architecture • This explains its popularity • Different from master/slave relationship! • Server software in server/client model does not control the network • Servers and clients operate independently Servers and clientsonly join for the request–response relationship Principles of Computer Networks and Communications

13. The Client/Server Model • Client/Server—how different types of software running on network devices interact • Examples • When you go to a website, your browser software (client) requests Web pages from the site’s Web server software (server) • You can download a file from an Internet server by using an FTP (file transfer protocol) client that requests the file from a server running FTP software (part of the TCP/IP protocol suite) • An application can be both a client and a server • One time requesting services and another time providing them This is common in peer-to-peer networks Principles of Computer Networks and Communications

14. The Challenge of Internetwork Addressing • Standardized protocols and procedures are key factors in Internet success • To send a message, the system must • Resolve the location of the recipient machine • Distinguish it from all the devices on the Internet • Computers on a shared medium LAN (not an internetwork) have unique flat physical addresses • Makes recipients easy to identify, but • Insufficient and impractical for internetworking! • Addresses do not contain any location information • System would have to search every network in the internetwork for the recipient machine Principles of Computer Networks and Communications

15. The Challenges of Internetwork Addressing • Hierarchical scheme • Different levels identify • A particular network of the internetwork • The physical machine address • Two architecture models • Open systems interconnection (OSI) model • The medium access control (MAC) sublayer of the data link layer handles physical addresses • Network layer handles logical addresses • Transmission control protocol over Internet protocol (TCP/IP) model • Follows the same pattern as OSI, but with possibly different labels • OSI data link layer is the TCP/IP data link or link layer • OSI network layer is the TCP/IP network or Internet layer Principles of Computer Networks and Communications

16. Hierarchical Addresses (Reviewing from Chapter6) • The postal system uses hierarchical addresses • Zip codes, states, cities, streets, names, etc. • Allows the post office to route mail in stages • Hierarchical network addresses similarly comprise groupings/segment • Allow the system to route messages to general areas, particular networks and subnetworks, and finally the destination machine • Addresses are constructed and routed in network layer (OSI) or internetwork layer (TCP/IP) Principles of Computer Networks and Communications

17. Hierarchical Addresses • Physical address is different from the network address • Physical address—refers to a particular device • The physical address doesn’t change when the device is moved • Network address—refers only to the network in which the device resides • The network address changes when the device is moved! • Analogy • An automobile VIN stays with the automobile (physical address) if you move to a different state • The license plate (network address) changes to be state-specific Principles of Computer Networks and Communications

18. Addressing in the Internet • Replaced NCP (network control protocol) • Major step towards today’s Internet • Explains why the Internet uses TCP/IP model architecture • TCP/IP • There is a single applications layer • Communications functions are in the other layers • OSI • Layers above transport focus on applications • Layers below session deal with communications “In 1983ARPANET officially adopted TCP/IP as the standard communications protocol.” Principles of Computer Networks and Communications

19. Focused on applications Focused on communications Model Architectures Fig. 12.2 Principles of Computer Networks and Communications

20. Addressing in the Internet • Internet protocol (IP) address • Used to identify a device for the Internet, in the internet layer • Different from a medium access control (MAC) address • IP address • Associated with a machine that may or may not be in a LAN • A logical address at the internet layer • May be changed without affecting the physical address • MAC address • A physical address at the data linklayer of a device on a LAN Principles of Computer Networks and Communications

21. Addressing in the Internet • IP address • Can be • Static • Assigned and fixed on the device by a network administrator • Dynamic • Assigned to a device by a protocol process when the device links (logs on) to the Internet • Dynamic IP addresses are recycled—released when a device disconnects and available for assignment on another device • Is used by the Internet to route packets • To reach a device, there must be a mapping of its IP address to its physical address In other words, the IP address must be associated with the device’s physical address Principles of Computer Networks and Communications

22. Addressing in the Internet • There are several protocols to do this mapping (i.e., IP address to physical address) • Address resolution protocol (ARP) • Reverse address resolution protocol (RARP) • Dynamic host configuration protocol (DHCP) )More about these in Chapter13…) Principles of Computer Networks and Communications

23. The Domain Name System • Domain name • The alphabet version of an IP address on the Internet • Domain name system (DNS) • Used by the internet to translate a domain name or e-mail address to an IP address • Every domain name and e-mail address • Is globally unique • Has a one-to-one relationship with a unique IP address • Resolving the domain name • The process where DNS translates a typed domain name into an IP address that the Internet uses to route the transmission For example, www.icann.org resolves (translates) into dotted quad notation as 192.0.34.65 Principles of Computer Networks and Communications

24. The Domain Name System • E-mail addresses • A computer program called a mail transfer agent sends e-mail from one computer or mail server to another • These agents use the DNS to find out where to deliver the email • Smooth operations in the DNS • DNS is an interconnected hierarchical system of high-speed servers running distributed domain name databases • For translation, this system simply searches its databases, finds the IP address for the name, and relays it back • Centralized organization keeps the DNS up to date Domain name registries are responsible for distributing domain names and IP addresses while ensuring their uniqueness Principles of Computer Networks and Communications

25. The Parts of a URL • Uniform resource locator (URL) • Is a symbolic meaning for specifying • a Web resource • The Web server on which the resource resides • The protocol that will be used to retrieve the resource • URL components are separated from each other by forward slashes, dots, and sometimes colons • Easiest to interpret from right to left • The rightmost segment is called the top-level domain (TLD) Principles of Computer Networks and Communications

26. Top-Level Domains (TLDs) www.users.alvernia.edu • Five original TLDs • .com for commercial enterprises • .gov for government sites • .net for organizations providing network services • .mil for use by the military • .org for nonprofit organizations and those that do not fit other designations • Because .com, .org, and .net characteristics have blurred over time, they are now referred to as generic TLDs (gTLDs) • TLD concept speeds up the searching process in the database because each partition is relatively small TLD Principles of Computer Networks and Communications

27. Domain and Sub-domain Names • Domain name www.users.alvernia.edu • Also called second-level domain • To the left of the TLD, separated by a dot • Specifies a particular network, an autonomous system (AS) within the Internet • Sub-domain name www.users.alvernia.edu • Narrows the location of the resource server Principles of Computer Networks and Communications

28. URL Server • Server (host) name www.users.alvernia.edu • Is located to the left of the sub-domain name • Holds the requested resource It is common practice to give the name www to the server that hosts Web documents However, it is not required! Principles of Computer Networks and Communications

29. Domain Name and URL Components www is a server at Baruch College Combined domain name.cuny.edu specifies a particular network within the Internet Fig 12.3 If you see a URL that ends after the TLD or after a subdirectory name, the extension/index.htm or /index.html is assumed Principles of Computer Networks and Communications

30. Specifying the File on the Server • Domain names • Specify location of the server • Do not explicitly specify the file (Web page) on the server • Beyond domain names • We need the path to the file on the server • Path must include directories and the file name • Path information is appended to the right of the TLD by a slash (/) Example www.users.alvernia.edu/students/finalgrades/index.htm • /students is the directory where Web files for students are stored • /finalgrades is the subdirectory where files specific to final grades are stored • /index.htm specifies one particular file Principles of Computer Networks and Communications

31. Specifying the File on the Server • .htm and .html • Indicate that the file is written in hypertext markup language (HTML) • Are default file names that are automatically searched for if no file name is given Any URL with nothing after the TLD or a subdirectory name assumes the extension /index.htm or /index.html Principles of Computer Networks and Communications

32. Specifying the File on the Server • Specifying the protocol in the URL • Leftmost segment of the URL defines actions taken in response to particular requests • http:// is one of the most common Web protocols • Stands for hypertext transfer protocol • In a browser, sends a command to the site’s Web server to download the page • Part of the application layer of the TCP/IP suite • A “stateless” protocol • Each command is performed independently • Makes it difficult to create sites that interact with users Principles of Computer Networks and Communications

33. The Http Protocol and “Cookies” • Software like Java is used to overcome “stateless” protocol difficulties • Used to write very small text files (cookies) to the client’s hard drive • Cookies contain “state” information • Allow a server application to understand the http requests that make up a continuous exchange Principles of Computer Networks and Communications

34. Other Identifiers • https:// • For sites that require secure transmissions, an s is added, indicating encryption • Unreachable without appropriate passwords • ftp (file transfer protocol) • Commonly employed protocol • Used for uploading and downloading files to and from ftp servers • ftp is typically in the server name, but not required • Country identifier • The country identification is part of the TLD, though separated from it by a dot • For example, BBC News has a United Kingdom identifier news.bbc.co.uk • When with the TLD, it is called a country code top-level domain (ccTLD) There are more than 240 ccTLDs! Principles of Computer Networks and Communications

35. IPv4 • IP addressing began with ARPANET • 1981 IPv4 became the standard we use today • Hierarchical scheme • Classes of addressesThree logical arrangements/splits of the bits reserved for addresses • For few organizations needing many host addresses • Few bits for network addresses, many for hosts • For many companies with many hosts • Many bits for network addresses, but also many for hosts • For the great many organizations with very few hosts • Many bits for network addresses, few for hosts Principles of Computer Networks and Communications

36. IPv4 Classful Addressing • “Classful”—most widely used type of IPv4 • Consists of 32 bits arranged in the dotted quad format • Four 8-bit sections • Makes up three unicastclasses • Unicast—from one source to one destination • Two-part addresses that split the 32-bits into network/host • Class A: 8 / 24 • Class B: 16 / 16 • Class C: 24 / 8 • Class identifier bits (prefixes) are included in the network address part of the split 192 .0 .34 .65 Principles of Computer Networks and Communications

37. Classful Addressing Prefixes • Prefixes • Identify class • Are not part of the IP address • Class A is 0 • Class B is 10 • Class C is 110 • D (not classful) is 1110 • E (not classful) is 1111 Principles of Computer Networks and Communications

38. IPv4 Classful Addressing These classes account for 87.5% of potentially available addresses Table 12.1 Principles of Computer Networks and Communications

39. IPv4 Non-Classful D and E • Two other categories of bits reserved for addresses • D and E are not segmented into networks and hosts • Both allow for 228 = 268,435,456 addresses • D • Multicasting • From a source to multiple destinations • E • Reserved for experimenting Principles of Computer Networks and Communications

40. Classful Addressing • An organization that applies for an IPv4 address • Receives a network address with a block of host addresses • The size of this block is determined by class • If the organization can handle more addresses than it actually uses, the other addresses associated with the company’s block go unused • Significant limitation to classful addressing • It wastes a lot of addresses Soon they will run out of addresses! To forestall this, classless addressing was implemented Principles of Computer Networks and Communications

41. Classful Addresses, Networks, Subnets, and Masks • Network ID • A company receives a network ID when a classful network address is assigned • Network ID + host address all 0s = network address • Used by outside routers to direct IP packets addressed to the company • Not assignable to any company host • No host ID can be all 0s • Logical IP networks • A company subdivides the classful network address to organize its own hosts Principles of Computer Networks and Communications

42. Subnets and Masks • Subnets • Logical networks with their own subnet addresses • Created by assigning hosts to groups with their own subnet addresses • Organized many ways—by building, floor, department Major advantage: • Masks • Bit patterns applied to entire addresses to isolate their components • Used to separate network, subnet, and host addresses • Have the same number of bits (arranged in dotted quad segments) as the IP address, but only use 1s and 0s A single IP address can connect a whole subnet to the Internet Principles of Computer Networks and Communications

43. Bitwise Multiplication and Masks • Bitwise multiplication of the address by the mask • Equivalent to applying the “and” operator • Captures address parts where mask bits are 1and ignores where they are 0 • Internet routers easily identify the IP address class by finding bit patterns this way Class B mask Principles of Computer Networks and Communications

44. Bitwise Multiplication and Masks • When the class is identified, a network default mask is applied • Three default masks • Class A mask: 255.0.0.0 • Class B mask: 255.255.0.0 • Class C mask: 255.255.255.0 Principles of Computer Networks and Communications

45. Bitwise Multiplication and Masks • In operation • After one of the three default masks is applied, the network address is revealed • The network address is assigned to the edge router of the organization • When a packet reaches any router, the appropriate mask is applied • If the network address it finds is not for that organization, the packet is passed to the next hop router • If the network and router addresses match, a subnet mask is applied Principles of Computer Networks and Communications

46. Addressing in the Internet • Subnet address • Comprises the network address + subnet mask bits • The remaining host address bits are all 0s • The total number of bits in the combined network and subnet addresses is indicated by a /n notation at the end of the address 130.57.110.9/19 = 19 bits 16 bits 3 bits Principles of Computer Networks and Communications

47. Classless Addresses • A solution to the IP address shortage? • Classless addressing • All of IPv4’s address space of 32 bits would be available without restriction • Twice as many addresses could be created • But addressing hierarchy and restrictions needed • Otherwise, routers would be overwhelmed and complicated Principles of Computer Networks and Communications

48. Classless Addresses • Classless inter-domain routing (CIDR) • The compromise between classful and classless • Allows any number of leftmost bits to be assigned as a network address • Addresses assigned based on the number of hosts a network can support; no class designation • CIDR is not limited to network addresses of 8,16,or 24 bits • CIDR is NOT perfect • Still wastes addresses, just not as many as classful addressing Principles of Computer Networks and Communications

49. CIDR, Subnetting, and Supernetting • Supernetting • CIDR’s hierarchical scheme that parallels subnetting • One key difference—it is applied to routing outside of the organization (hence the name) • Is a method of route aggression • A single high-level routing table entry represents many lower-level routes • Internet backbone routers need fewer entries • More efficient, eases table size requirements Principles of Computer Networks and Communications

50. IPv6 • Uses a 128-bit address sequence instead of 32 • Provides IP header extensions • Adds quality of service (QoS) labeling to IP packets • Uses coloned octal, not dotted quad • Accommodates CIDR by adding a (an) /n to the end of the address Principles of Computer Networks and Communications