Chapter 4 Internet Addressing and Operation

1. Chapter 4 Internet Addressing and Operation Part 1: Data Communications in the Information Age

2. Internal Addressing Internet naming conventions Subnet masks Static vs. dynamic IP addresses IP routing Internet tools for network managers Web page design tools Server configurations TCP/IP and security Topics Addressed in Chapter 4

3. Internet Addresses • IPv4 is currently the standard for IP addressing • IPv4 addressing is described in RFC 760 • 32-bit addresses are specified • IPv6 addresses are 128-bits in length • IPv6 is used in Internet2 and will be more widely used in the future on the Internet • IP addressing is primarily concerned with establishing a unique identity for networked computers • By doing this, IP addressing enables packets to be routed between networks and delivered to the appropriate host or node on the destination network

4. IP Addressing Basics • IPv4 addresses are usually written as four separate numbers delineated by a period • For example: 101.209.33.17 • This way of representing an IP address is called the dotted-quad notation • Each number in the four-number group is represented as an 8-bit octet in an IPv4 header • For example: 101.209.33.17 would be represented as: • 01100101 11010001 00100001 00010001

5. More IP Addressing Basics • In IPv4, each 32-bit IP address is subdivided into network and host/node portions • This is illustrated in Figure 4-2 • The composition of the first four bits in the IP address specifies whether the network portion is 1, 2, or 3 bytes in length • These four bits determine whether the host/node has a Class A, B, C, D, E address (see Table 4-1)

6. Figure 4-2

7. IPv4 Address ClassesTable 4-1

8. IPv4 ClassesTable 4-2

9. Reserved IP Addresses • The developers of the IPv4 addressing scheme reserved three blocks of addresses for networks that would not be connected to the Internet • These are identified and defined in RFC 1918 • Reserved address ranges are illustrated in Table 4-3

10. Table 4-3

11. Domain Names • For most Internet users, dotted-quad representations for Internet hosts/nodes are cumbersome. As a result, most users rely on domain name conventions instead • Domain names are included in URLs • A domain name is a word-orientated representation of an Internet address • ICANN is responsible for approving domain names, including abbreviations used in URLs

12. Domain Name Conventions • The address elements of a domain name are ordered from most to least specific • For example, in frodo.mycompany.com.us • frodo probably represents the name of an Internet host owned by the company mycompany • The com identifies the mycompany entity as a company and us identifies the country in which the host’s network is located • The hierarchical nature of domain names is illustrated in Figure 4-3

13. The Hierarchical Nature of Domain NamesFigure 4-3

14. Domain Names and URLs • When a domain name is included in a URL, it must be resolved to an IP address • This is done by the Internet’s Domain Name System (DNS) • Domain names and their IP addresses are stored in databases on domain name servers • When a domain name must be resolved, a message is sent to the closest domain name server to obtain the IP address. If that server does not know the IP address, it sends a request to other domain servers for the information • Once the IP address for a domain name is known, the host/node inserts the IP address as the destination address for the packet so that it can be routed to appropriate recipient

15. URL Protocols • HTTP is not the only TCP/IP protocol that uses URLs • Others are identified in Table 4-7 • Although these differ slightly in format (see Table 4-8), all use domain names and therefore rely on the Domain Name System in order to operate

16. Table 4-7

17. Table 4-8

18. Subnet Addressing • Because there is a limited number of available IPv4 addresses, IPv4 developers provided mechanisms for sharing a single network address among two or more subnets • These mechanisms are described in RFC 950 • RFC 950 enables class A, B, and C networks to be split into smaller networks that use the same network assignment numbers

19. Subnetting Advantages • Subnetting has the following advantages: • It simplifies network administration; each network segment can be maintained independently and efficiently • Intranets can be restructured without affecting the overall network’s interfaces with the Internet and other external networks • Because intranet subnetting is not visible to external networks it can be used to enhance the overall security of the organization’s networks

20. Subnetting Basics • Subnetting enables network managers to extend the network portion of IPv4 addresses by taking away a portion of the host/node portion of the IP address • The portion that is taken away is used as a subnet identifier • This is illustrated in Figure 4-4

21. Figure 4-4

22. Subnet Masks • A subnet mask is a binary bit pattern that is stored in hosts, nodes, and routers • It is matched up with an incoming packet’s destination IP address to determine whether to accept or reject the packet • Every TCP/IP network host/node or router stores a subnet mask along with its IP address (see Figure 4-6) • The subnet mask specifies which bits in an IP address should be treated as an extended network address (network + subnet) and which bits represent the host/node portion of the address • Default subnet masks exists for class A, B, and C networks (see Table 4-9) • Table 4-10 summarizes alternative class C subnet masks • Figure 4-5 illustrates how a subnet mask is used to decompose an IPv4 address into its subnet and host/node addresses

23. Figure 4-6

24. Table 4-9 Table 4-10

25. Figure 4-5

26. Static vs. Dynamic IP Addresses • Host/node addresses can be allocated in one of two ways: • Static assignments • Dynamic assignments • Static IP addresses are permanently assigned to hosts and node • Servers and routers are typically assigned static IP addresses • These can be assigned to hosts/nodes through manual configuration or by always assigning the same IP address to a particular host/node when it comes online • Dynamic IP addresses are automatically assigned to client stations in a TCP/IP network when they come online • DHCP servers assign dynamic IP addresses to clients

27. Dynamic Host Configuration Protocol (DHCP) • The most common approach for dynamically assigning IP addresses is DHCP (Dynamic Host Configuration Protocol) • Each DHCP server has a range of IP addresses that can be assigned and maintains a list of currently assigned and currently unassigned IP addresses • DHCP client software enables a network host/node to request an IP address from a DHCP server when it comes online • This process is illustrated in Figure 4-9 • When the client goes offline, it notifies the DHCP server that it is releasing the IP address. Once released, the IP address is placed on the DHCP server’s assignable address list

28. Figure 4-9

29. Internet Addressing in LANs • Additional addressing processes take place when the host/node that needs to connect to the Internet is in a LAN • In LANs, physical (MAC) addresses (the address of the computers’ network interface cards) are used for message delivery • When a LAN host/node has both an IP address and a MAC address, an incoming IP packet can only be delivered to the computer after the IP address has been translated to a MAC address • The protocol that performs this function is address resolution protocol (ARP)

30. Address Resolution Protocol (ARP) • ARP servers maintain tables that contain host/node IP addresses and corresponding MAC addresses (see Table 4-12) • If the destination node’s IP address is in the ARP table, it extracts the corresponding MAC address and uses it to build the MAC header needed to send the message to the node • ARP is found at the Internet layer of the TCP/IP protocol stack (see Figure 4-10) but is often described as overlapping the Internet and media access layers because of its role in translating IP to MAC addresses

31. Table 4-12

32. Figure 4-10

33. IP Routing • Routers leverage routing tables when determining how to route a packet to the destination node’s IP address • Some of the information found in routing tables is found in Table 4-13 • Essentially, when a router receives a packet, it: • identifies the destination node’s IP address in the packet header • consults the routing table to determine the best path to the destination node’s network across the Internet backbone • Addresses the packet to the next router on the best path and transmits the packet out the appropriate port • This process is illustrated in Figure 4-12

34. Figure 4-12

35. Ports and Sockets • Once received by the destination host/node, a packet progresses up the layers of the TCP/IP protocol stack and is directed to the appropriate application • Port numbers are included in TCP or UDP headers to identify the application layer protocol that generated the data in the packet • Some port numbers are permanently assigned to applications/services (see Table 4-15) • The combination of an IP address and a port number is called a socket • For example, the socket notation for a Web page request on a Web server whose IP address is 141.165.231.193 would be 141.165.231.193:80

36. Examples of Well-Known PortsTable 4-15

37. Internet Tools for Network Managers • Some of the Internet tools used by network managers include: • Finger (see Table 4-16) • Ping (see Figure 4-13) • Tracert (see Figure 4-14) • WHOIS database

38. Internet ToolsTable 4-16 & Figure 4-13

39. Figure 4-14

40. Web Page Design Tools • Some of the major Web page design tools include: • Hypertext Markup Language (HTML) • Dynamic HTML (DHTML) • Extensible Markup Language (XML) • see Table 4-17 and Figure 4-16 • Vector Markup Language (VML) • Precision Graphics Markup Language (PGML) • Virtual Reality Markup Language (VRML) • These all evolved from SGML (see Figure 4-15) • GIF, JPEG, and PNG are examples of graphics files used by Web page designers (see Table 4-18)

41. Server Configurations • At large commercial Web sites, a group of servers may share a single URL. This collective “host” is called a server farm • Server farms help ensure reliable access and fault tolerance • Load balancing involves the use of a switch or router to transfer user requests to particular servers in a server farm (see Figure 4-17) • In a server cluster, a group of servers acts as a single team and is responsible for allocating the total workload that they are responsible for handling

42. Figure 4-17

43. TCP/IP and Security • Important TCP/IP security technologies include: • Proxy servers that stand between the Internet and a private network and help prevent outsiders from accessing internal addresses and other network details (see Figure 4-18) • Network address translation (NAT) is an important proxy server capability • Virtual private networks (VPNs) that use tunneling protocols, authentication, and encryption to establish private links for a corporate network across the Internet and other public networks • IPSEC (Internet Protocol Security Architecture) that provides secure data transmission across IP networks via authentication and encryption (see Figure 4-19)

44. Figure 4-18

45. Figure 4-19

46. IPSEC Uses • Because IPSEC enables secure communications across public TCP/IP networks such as the Internet, it is used to: • Build secure VPNs among branch offices • Implement secure remote access for teleworkers • Create secure extranets with business partners • Provide security for B2B e-commerce, e-mail, file transfers, remote logons, and other distributed applications

47. Chapter 4 Internet Addressing and Operation Part 1: Data Communications in the Information Age