number one million. Since one million is greater than the largest value that can be held in two bytes, 65535, at least three bytes will be needed. By multiplying by two until 24 bits, three bytes, is reached, the value will be 8,388,608. This means that the largest value that 24 bits can hold is 16,777,215. So starting at the 24-bit, follow the process until zero is reached. Continuing with the procedure described, it is determined that the decimal number one million is equal to the binary number 00001111 01000010 01000000. Figure includes some decimal to binary conversion exercises. Binary to decimal conversion is just the opposite. Simply place the binary in the table and if there is a one in a column position add that value into the total. Convert 00000100 00011101 to decimal. The answer is 1053. Figure includes some decimal to binary conversion exercises. Web Links Binary Numbers http://www.netlingo.com/more/binary.html
Content 9.2 Internet Addresses 9.2.3 IPv4 addressing A router forwards packets from the originating network to the destination network using the IP protocol. The packets must include an identifier for both the source and destination networks. Using the IP address of destination network, a router can deliver a packet to the correct network. When the packet arrives at a router connected to the destination network, the router uses the IP address to locate the particular computer connected to that network. This system works in much the same way as the national postal system. When the mail is routed, it must first be delivered to the post office at the destination city using the zip code. That post office then must locate the final destination in that city using the street address. This is a two-step process. Accordingly, every IP address has two parts. One part identifies the network where the system is connected, and a second part identifies that particular system on the network. As is shown Figure , each octet ranges from 0 to 255. Each one of the octets breaks down into 256 subgroups and they break down into another 256 subgroups with 256 addresses in each. By referring to the group address directly above a group in the hierarchy, all of the groups that branch from that address can be referenced as a single unit. This kind of address is called a hierarchical address, because it contains different levels. An IP address combines these two identifiers into one number. This number must be a unique number, because duplicate addresses would make routing impossible. The first part identifies the system's network address. The second part, called the host part, identifies which particular machine it is on the network. IP addresses are divided into classes to define the large, medium, and small networks. Class A addresses are assigned to larger networks. Class B addresses are used for medium-sized networks, and Class C for small networks. The first step in determining which part of the address identifies the network and which part identifies the host is identifying the class of an IP address. Interactive Media Activity Drag and Drop: Identifying Address Classes After completing this activity, the student will be able to identify all the details within the different internet address classes. Web Links IP Addressing Basics http://www.winntmag.com/Articles/ Index.cfm? ArticleID=7035
Content 9.2 Internet Addresses 9.2.4 Class A, B, C, D, and E IP addresses To accommodate different size networks and aid in classifying these networks, IP addresses are divided into groups called classes. This is known as classful addressing. Each complete 32-bit IP address is broken down into a network part and a host part. A bit or bit sequence at the start of each address determines the class of the address. There are five IP address classes as shown in Figure . The Class A address was designed to support extremely large networks, with more than 16 million host addresses available. Class A IP addresses use only the first octet to indicate the network address. The remaining three octets provide for host addresses. The first bit of a Class A address is always 0. With that first bit a 0, the lowest number that can be represented is 00000000, decimal 0. The highest number that can be represented is 01111111, decimal 127. The numbers 0 and 127 are reserved and cannot be used as network addresses. Any address that starts with a value between 1 and 126 in the first octet is a Class A address. The 127.0.0.0 network is reserved for loopback testing. Routers or local machines can use this address to send packets back to themselves. Therefore, this number cannot be assigned to a network. The Class B address was designed to support the needs of moderate to large-sized networks. A Class B IP address uses the first two of the four octets to indicate the network address. The other two octets specify host addresses. The first two bits of the first octet of a Class B address are always 10. The remaining six bits may be populated with either 1s or 0s. Therefore, the lowest number that can be represented with a Class B address is 10000000, decimal 128. The highest number that can be represented is 10111111, decimal 191. Any address that starts with a value in the range of 128 to 191 in the first octet is a Class B address. The Class C address space is the most commonly used of the original address classes. This address space was intended to support small networks with a maximum of 254 hosts. A Class C address begins with binary 110. Therefore, the lowest number that can be represented is 11000000, decimal 192. The highest number that can be represented is 11011111, decimal 223. If an address contains a number in the range of 192 to 223 in the first octet, it is a Class C address. The Class D address class was created to enable multicasting in an IP address. A multicast address is a unique network address that directs packets with that destination address to predefined groups of IP addresses. Therefore, a single station can simultaneously transmit a single stream of data to multiple recipients. The Class D address space, much like the other address spaces, is mathematically constrained. The first four bits of a Class D address must be 1110. Therefore, the first octet range for Class D addresses is 11100000 to 11101111, or 224 to 239. An IP address that starts with a value in the range of 224 to 239 in the first octet is a Class D address. A Class E address has been defined. However, the Internet Engineering Task Force (IETF) reserves these addresses for its own research. Therefore, no Class E addresses have been released for use in the Internet. The first four bits of a Class E address are always set to 1s. Therefore, the first octet range for Class E addresses is 11110000 to 11111111, or 240 to 255. Figure shows the IP address range of the first octet both in decimal and binary for each IP address class. Lab Activity Lab Exercise: IP Addressing Basics This lab is to name the five different classes of IP addresses and to describe the characteristics and use of the different IP address classes. Web Links IP Addressing Basics http://www.winntmag.com/Articles/ Index.cfm? ArticleID=7035
Content 9.2 Internet Addresses 9.2.5 Reserved IP addresses Certain host addresses are reserved and cannot be assigned to devices on a network. These reserved host addresses include the following: