Understanding Networks

1. Understanding Networks

2. Objectives • Compare client and network operating systems • Learn about local area network technologies, including Ethernet, Token Ring, FDDI, and wireless • Use the OSI model to understand networking • Learn how network computers and servers are addressed

3. TCP/IP Protocols at Each Layer • TCP/IP covers the first five layers of the OSI model, and is included in an operating system as a group of utilities called the TCP/IP stack. • Figure 5-41 shows the four major groupings of the OSI model as applied to TCP/IP networks.

4. Protocols at the Application, Presentation, and Session Layers • The first three layers of the OSI model are handled by the protocol specific to the application using it and are best treated as a single group rather than unique layers. • Web browsers, e-mail, chat rooms, and FTP software are examples of the applications that use the Internet. • The language or protocol each of these applications uses is listed at the Application, Presentation, and Session layers.

5. Protocols at the Transport Layer • A TCP/IP network has two protocols that work at the Transport layer; one protocol guarantees delivery and the other does not. • With TCP/IP, the protocol that guarantees delivery is TCP and the protocol that does not is UDP (User Datagram Protocol). • TCP is used for client and server requests and responses.

6. Protocols at the Transport Layer (Continued) • Because TCP establishes a connection, it is called a connection-oriented protocol. • UDP is a protocol that sends data without caring about whether the data is received. • It does not establish a connection first; thus, it is called a connectionless protocol.

7. Protocols at the Network Layer • TCP and UDP communicate with the Network layer, which is sometimes called the Internet layer. • Some of the other supporting protocols include ARP (Address Resolution Protocol), responsible for locating a host on a LAN; RARP (Reverse Address Resolution Protocol), responsible for discovering the Internet address of a host on a LAN; and ICMP (Internet Control Message Protocol), responsible for communicating problems with transmission to devices that need to know about these problems.

8. Protocols at the Data Link and Physical Layers • PPP (Point-to-Point Protocol) is used over telephone lines, and allows a computer to connect to a network using a modem. • PPP is the most popular protocol for managing network transmission from one modem to another.

9. MAC Addresses • MAC addresses function at the lowest (Data Link) networking level. • If a host does not know the MAC address of another host on a local area network, it uses the operating system to discover the MAC address.

10. IP Addresses • All the protocols of the TCP/IP suite identify a device on the Internet or an intranet by its IP address. • An IP address is 32 bits long, made up of 4 bytes separated by periods. • Within an IP address, each of the four numbers separated by periods is called an octet. • The first part of an IP address identifies the network, and the last part identifies the host.

11. Classes of IP Addresses • IP addresses that can be used by companies and individuals are divided into three classes: Class A, Class B, and Class C, based on the number of possible IP addresses in each network within each class. • The group of IP addresses assigned to an organization are unique to all other IP addresses on the Internet and are available for use on the Internet. • The IP addresses available to the Internet are called public IP addresses.

12. Private IP Addresses • Private IP addresses are IP addresses that are assigned by a network administrator for use on private intranets that are isolated from the Internet. • The RFC 1918 recommends that the following IP addresses be used for private networks: • 10.0.0.0 through 10.255.255.255 • 172.16.0.0 through 172.31.255.255 • 192.168.0.0 through 192. 168. 255.255

13. Dynamically Assigned IP Addresses • Instead of IP addresses permanently being assigned to computers (called static IP addresses), an IP address is assigned for the current session only (called a dynamic IP address). • Internet service providers (ISPs) are organizations through which individuals and businesses connect to the Internet.

14. Network Address Translation • If the hosts on a network using private IP addresses need to access the Internet, a problem arises because the private IP addresses are not allowed on the Internet. • The solution is to use NAT (Network Address Translation), which uses a single public IP address to access the Internet on behalf of all hosts on the network using other IP addresses.

15. Plans for New IP Addresses • Because of an impending shortage of IP addresses, as well as some limitations in the current standards for IP, a new scheme of IP addresses called the IPv6 (IP version 6) standard is currently being developed and implemented. • Current IP addresses using the current IPv4 (IP version 4) have 32 bits with eight bits in each of four octets.

16. Plans for New IP Addresses (Continued) • With the new system, each address segment can have 32 bits, for a total of 128 bits for the entire address. • A disadvantage of IPv6 is the fact that so much software used on the Internet would become outdated because current software is designed to hold 32-bit IP addresses and, with the new system, this number would no longer be sufficient.

17. Ports • A port is a number used to address software or services running on a computer. • A host computer might have several services running on it. • Each server running on the host is assigned a port. • The port is written at the end of the IP address, separated from the IP address with a colon—like this: 169.49.209.19.80.

18. Tying It All Together: How Data Travels on the Network • The Web browser wants to make a request to a Web server, and processes the request using an API call. • The API process packages the data using HTTP format, which includes an HTTP header, and addresses it to an IP address and port 80, which is the default port for a Web server. • HTTP delivers the package to TCP, giving the destination IP address and port.

19. Tying It All Together: How Data Travels on the Network (Continued) • TCP guarantees delivery, and attempts to make a connection to the destination IP address and port using the three-way handshake. • With the first attempt that TCP makes to communicate with the remote host, the first packet reaches the Network layer and IP uses ARP to resolve the IP address to a MAC address. • When a packet reaches a hub on the Ethernet LAN, the hub replicates the packet and sends it to every device to which it is connected.

20. Tying It All Together: How Data Travels on the Network (Continued) • When the IP layer receives a broadcast packet, it decides if it is appropriate to respond. • After it knows the MAC address, it can send the first packet to make the connection. • It prepares the data by attaching a TCP header in front of the data.

21. Summary • The two approaches to managing network resources are peer-to-peer and client/server. • Windows 2000 Server and Windows Server 2003 support multiple domain controllers. • Windows XP has three operating systems: Windows XP Professional, Windows XP Home Edition, and Windows XP 64-Bit Edition. • The most popular network technology used today is Ethernet; it can be configured either as a star or bus.

22. Summary (Continued) • An IP address can be permanently assigned to a device (static IP addressing) or a different IP address can be assigned each time the device logs on to the network (dynamic IP addressing). • When a host is configured to used TCP/IP, and IP address is bound to the MAC address. • A proxy server uses NAT to substitute its own public IP address for the private IP address of a computer on the network that is requesting Internet access.