lass B Network Class C Network Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. X.25, Internets, Intranets, and Extranets Chapter 7 Class B addresses use a 16-bit network number (the first two bits are reserved and set to 10), leaving a 14-bit network number and a 16-bit host address. Class C addresses use a 24-bit address for the network number (the first three bits are set to 110, leaving the network address field at 21 bits long) followed by an 8-bit host address. Like anything else in a network SO widely deployed worldwide, a problem looms in the future. We are running out of address numbers! In the newest version of IP, called IP New Generation or IP Version 6, the address field is expanded to a 128-bit address field for every source and destination node on the network. Figure 7-22 shows the IP Version 6 header. IP Subnetworking and Masking When using TCP/IP on a network, a subnetwork address and a masking of the network and host addresses can be used. The subnetwork address can be assigned on a departmental basis. Using subnetworking, an organization can use a class B address and then subnetwork each individual LAN or department with a class C address, as shown in Figure 7-23. The subnet address can advise the routing devices to ignore the parts of the network not needed to route the data from one network to another. This is more effi- cient than having to use the entire address when searching the routing tables. If a network administrator has chosen to use 8 bits of subnetting, the third octet of a class B IP address provides the subnet number. For exam- 4 bits 4 bits 24 bits Figure 7-22 IPV6 headers. Version Priority Flow Label 16 bits 8 bits 8 bits Payload Length Next Header Hop Limit 128 bits Source Address 128 bits Destination Address Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copy