CIT232©IFM-CIT Dept The Internet

CIT232©IFM-CIT Dept Know how the Internet began. Understand the architecture of today’s Internet and its relation- ship with ISPs. Understand the importance of the TCP/IP protocol suite. OBJECTIVES Understand the role of IP, UDP, and TCP in the Internet. Understand the difference between the Internet, an intranet, and an extranet.

CIT232©IFM-CIT Dept Internet History The internet traces its origins to a military network called ARPANET. ARPANET was created in response to an increased need for national security, and the need to connect remote computing resources. After ARPARET, other private network sprang up, and eventually all of these networks were connected. The connection of these networks formed what we call the Internet. Read the handout

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CIT232©IFM-CIT Dept Internet Terms 1.Internet 2.Packet Switching Network 3.Modem - Modulator/Demodulator

CIT232©IFM-CIT Dept Internet: is the global collection of computers, communication systems, and software. Public telephone system connects all this equipment to form the internet Packet Switched Network: On a packet switched network, the data is closed in electronic packet. Each packet is individually addressed and forwarded across the network. Modem: Modem stands for modulator/demodulator. Modems are used to send data from a computer over the telephone lines. Computers use digital technology, and the telephone system usually uses analog technology

CIT232©IFM-CIT Dept How the Internet Works Internet is the Packet Switched Network Data sent in packets Each packet has an IP address 1.Every computer in the Network has an address called an IP address. 2.IP- Internet Protocol; 3.IP defines the rules of sending communication across the network

CIT232©IFM-CIT Dept 1.Internet is the switched network means data sent over internet is encapsulated in packets 2.The packets are addressed according to their destination 3.Internet database keep track of the addresses and allow networking equipment to forward packet to the correct computer. 4.This analogy to telephone systems. Internet is the Packet Switched Network

CIT232©IFM-CIT Dept Basic Internet Architecture

CIT232©IFM-CIT Dept Peering »ISPs at the same level usually do not charge each other for exchanging messages Higher level ISPs charge lower level ones –National ISPs charge regional ISPs which in turn charge local ISPs Local ISPs charge individuals and corporate users for access Packet Exchange Charges

CIT232©IFM-CIT Dept Connecting to an ISP Done by through ISP’s Point of Presence (POP) –A place ISP provides service to its customers Individual users –Typically through a dial-up line using the PPP protocol Handled by the ISP’s modem pool –Userid and password checked by Remote Access Server (RAS) Once logged in, the user can send packets over the phone line Corporate users –Typically access the POP using a T-1, T-3 or ATM OC- 3 connections provided by a common carrier Cost = ISP charges + circuit charges

CIT232©IFM-CIT Dept Internet today

CIT232©IFM-CIT Dept Technical Focus: Maturity Levels of an RFC An RFC, during its lifetime, falls into one of six maturity levels: proposed standard, draft standard, Internet standard, historic, experimental, and informational.

CIT232©IFM-CIT Dept Internet administration

CIT232©IFM-CIT Dept Internet Society ISOC: Is an international, nonprofit organization formed 1992 to provide support for internet standard process. ISOC supports other Internet administrative bodies such as IAB, IETF, IRTF and IANA. ISOC also promotes research and other scholarly activities related to the internet IAB - Internet Architecture Board IETF - Internet Engineering Task Force IRTF - Internet Research Task Force IANA - Internet Assign Number Authority

CIT232©IFM-CIT Dept TCP/IP protocol suite IP: handle datagram routing TCP:is responsible for higher level functions such as segmentation, reassembling, and error detection.

CIT232©IFM-CIT Dept IP datagram

CIT232©IFM-CIT Dept Technical Focus: Inside the Header of an IP Datagram An IP datagram contains several fields. The most important are the source and destination addresses of the datagram (IP addresses). The header also contains fields related to fragmentation. The size of a datagram may be too large for some LAN or WAN protocols. In this case, the datagram is divided into fragments; each fragment carries the same identification number as well as other information to help the receiver assemble the datagram. The header also has two length fields; one defines the length of the header, the other defines the length of the entire packet. One field that can decrease traffic on the Internet holds the number of routers a packet can visit before it is discarded. The header also contains a checksum field to determine the validity of the packet.

CIT232©IFM-CIT Dept IP Address

CIT232©IFM-CIT Dept 4.1 INTRODUCTION 1.The identifier used in the IP layer of the TCP/IP protocol suite to identify each device connected to the Internet is called the Internet address or IP address. 2.An IP address is a 32-bit address that uniquely and universally defines the connection of a host or a router to the Internet. 3.IP addresses are unique. They are unique in the sense that each address defines one, and only one, connection to the Internet. 4.Two devices on the Internet can never have the same address. Introduction

CIT232©IFM-CIT Dept An IP address is a 32-bit address. 8-bit IP- address is normally written as four decimal number separated by dots (called dotted - decimal notation)

CIT232©IFM-CIT Dept The address space of IPv4 is 2 32 or 4,294,967,296.

CIT232©IFM-CIT Dept CLASSFUL ADDRESSING Classful addressing includes the following: Recognizing ClassesRecognizing Classes Netid and HostidNetid and Hostid Classes and BlocksClasses and Blocks Network AddressesNetwork Addresses Sufficient InformationSufficient Information MaskMask

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CIT232©IFM-CIT Dept Addresses per class

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CIT232©IFM-CIT Dept Find the class of each address: a b c d e Example 7 Solution a. The first byte is 227 (between 224 and 239); the class is D. b. The first byte is 193 (between 192 and 223); the class is C. c. The first byte is 14 (between 0 and 127); the class is A. d. The first byte is 252 (between 240 and 255); the class is E. e. The first byte is 134 (between 128 and 191); the class is B.

CIT232©IFM-CIT Dept Netid and hostid

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CIT232©IFM-CIT Dept The number of addresses in class C is smaller than the needs of most organizations.

CIT232©IFM-CIT Dept Class D addresses are used for multicasting; there is only one block in this class.

CIT232©IFM-CIT Dept Class E addresses are reserved for future purposes; most of the block is wasted.

CIT232©IFM-CIT Dept In classful addressing, the network address (the first address in the block) is the one that is assigned to the organization. The range of addresses can automatically be inferred from the network address.

CIT232©IFM-CIT Dept Given the network address , find the class, the block, and the range of the addresses. Example 9 Solution The class is A because the first byte is between 0 and 127. The block has a netid of 17. The addresses range from to

CIT232©IFM-CIT Dept Given the network address , find the class, the block, and the range of the addresses. Example 10 Solution The class is B because the first byte is between 128 and 191. The block has a netid of The addresses range from to

CIT232©IFM-CIT Dept Given the network address , find the class, the block, and the range of the addresses. Example 11 Solution The class is C because the first byte is between 192 and 223. The block has a netid of The addresses range from to

CIT232©IFM-CIT Dept Masking concept

CIT232©IFM-CIT Dept AND operation

CIT232©IFM-CIT Dept Default masks

CIT232©IFM-CIT Dept The network address is the beginning address of each block. It can be found by applying the default mask to any of the addresses in the block (including itself). It retains the netid of the block and sets the hostid to zero.

CIT232©IFM-CIT Dept Given the address , find the beginning address (network address). Example Solution The default mask is , which means that only the first byte is preserved and the other 3 bytes are set to 0s. The network address is

CIT232©IFM-CIT Dept Given the address , find the beginning address (network address). Exampl e Solution The default mask is , which means that the first 2 bytes are preserved and the other 2 bytes are set to 0s. The network address is

CIT232©IFM-CIT Dept Given the address , find the beginning address (network address). Example 14 Solution The default mask is , which means that the first 3 bytes are preserved and the last byte is set to 0. The network address is

CIT232©IFM-CIT Dept Note that we must not apply the default mask of one class to an address belonging to another class. Note:

CIT232©IFM-CIT Dept 4.3 OTHER ISSUES In this section, we discuss some other issues that are related to addressing in general and classful addressing in particular. The topics discussed in this section include: Multihomed Devices Location, Not Names Special Addresses Private Addresses Unicast, Multicast, and Broadcast Addresses

CIT232©IFM-CIT Dept Figure 4.12 Multihomed devices

CIT232©IFM-CIT Dept Table 4.3 Special addresses

CIT232©IFM-CIT Dept Figure 4.13 Network address

CIT232©IFM-CIT Dept Figure 4.14 Example of direct broadcast address

CIT232©IFM-CIT Dept Figure 4.15 Example of limited broadcast address

CIT232©IFM-CIT Dept Figure 4.16 Examples of “this host on this network”

CIT232©IFM-CIT Dept Figure 4.17 Example of “specific host on this network”

CIT232©IFM-CIT Dept Figure 4.18 Example of loopback address

CIT232©IFM-CIT Dept Table 4.5 Addresses for private networks

CIT232©IFM-CIT Dept Multicast delivery will be discussed in depth in Chapter 15. Note:

CIT232©IFM-CIT Dept Table 4.5 Category addresses

CIT232©IFM-CIT Dept Table 4.6 Addresses for conferencing

CIT232©IFM-CIT Dept Figure 4.19 Sample internet

CIT232©IFM-CIT Dept 4.4 SUBNETTING AND SUPERNETTING In the previous sections we discussed the problems associated with classful addressing. Specifically, the network addresses available for assignment to organizations are close to depletion. This is coupled with the ever-increasing demand for addresses from organizations that want connection to the Internet. In this section we briefly discuss two solutions: subnetting and supernetting. The topics discussed in this section include: SubnettingSupernetting Supernet Mask Obsolescence

CIT232©IFM-CIT Dept IP addresses are designed with two levels of hierarchy. Note:

CIT232©IFM-CIT Dept Figure 4.20 A network with two levels of hierarchy (not subnetted)

CIT232©IFM-CIT Dept Figure 4.21 A network with three levels of hierarchy (subnetted)

CIT232©IFM-CIT Dept Figure 4.22 Addresses in a network with and without subnetting

CIT232©IFM-CIT Dept Figure 4.23 Hierarchy concept in a telephone number

CIT232©IFM-CIT Dept Figure 4.24 Default mask and subnet mask

CIT232©IFM-CIT Dept What is the subnetwork address if the destination address is and the subnet mask is ? Example 15 Solution We apply the AND operation on the address and the subnet mask. Address ➡ Subnet Mask ➡ Subnetwork Address ➡

CIT232©IFM-CIT Dept Figure 4.25 Comparison of a default mask and a subnet mask

CIT232©IFM-CIT Dept Figure 4.26 A supernetwork

CIT232©IFM-CIT Dept In subnetting, we need the first address of the subnet and the subnet mask to define the range of addresses. In supernetting, we need the first address of the supernet and the supernet mask to define the range of addresses. Note:

CIT232©IFM-CIT Dept Figure 4.27 Comparison of subnet, default, and supernet masks

CIT232©IFM-CIT Dept The idea of subnetting and supernetting of classful addresses is almost obsolete. Note:

CIT232©IFM-CIT Dept Internet address

CIT232©IFM-CIT Dept Technical Focus: Classful versus Classless Addressing With more and more organizations wanting to use the Internet, the Internet authorities are running out of IP addresses. Internet addresses were originally designed as classful addresses. By this, we mean that the total number of 32-bit addresses was divided unevenly into five classes: A, B, C, D, and E. Class A and B contain blocks of addresses with a very large range. Each block is granted to one organization, but most of these organizations never use their allotted number of addresses. This is a tremendous waste of addresses. Recently, a new design called classless addressing has been implemented. In this design, all available addresses are put into a big pool; each organization is granted a range of addresses according to its need.

CIT232©IFM-CIT Dept Figure 13-6 A part of the Internet

CIT232©IFM-CIT Dept Figure 13-7 UDP user datagram

CIT232©IFM-CIT Dept Technical Focus: Inside a UDP header The header of the UDP datagram is very simple: it contains only four fields. One field defines the application program that has sent the packet (the source), and another defines the application program that is to receive the packet (the destination). Another field defines the length of the entire packet. The last field carries a checksum for error detection.

CIT232©IFM-CIT Dept Figure 13-8 TCP segment format

CIT232©IFM-CIT Dept Technical Focus: Inside a TCP Segment Header The header of a segment is very complicated and contains optional as well as mandatory fields. We briefly discuss just the required fields. One pair of fields defines the source and destination application programs. Another pair is used for error and flow control; one holds the unique sequence number, and the other holds the acknowledgment number. One field defines the size of the sliding window in the transport layer. The sliding window in the transport layer uses the same concept as the one in the data link layer (see Chapter 5). There are also flags that define the purpose of the segment (for connection establishment, for termination, for acknowledgment, and so on). The last required field carries a checksum for error detection.

CIT232©IFM-CIT Dept NEXTGENERATIONNEXTGENERATION 13.3

CIT232©IFM-CIT Dept ACCESS TO THE INTERNET INTERNET 13.4

CIT232©IFM-CIT Dept PRIVATE NETWORKS: INTRANET AND EXTRANET PRIVATE NETWORKS: INTRANET AND EXTRANET 13.5

CIT232©IFM-CIT Dept Technical Focus: Network Address Translation (NAT) A technology that is related to private networks is network address translation (NAT). The technology allows a site to use a set of private addresses for internal communication and a set of (at least one) global Internet addresses for communication with other sites.