w-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 device with the IP address responds. It sends back a message to use the fol- lowing MAC address, as shown in Figure 7-18. All other devices on the sub- net hear the request and the response, and then update a table in their appropriate memory. RARP uses broadcast messages to determine the Internet address asso- ciated with a particular hardware address, as shown in Figure 7-19. RARP is particularly important to diskless nodes, which may not know their inter- network address when they boot. The response is sent, which is shown in Figure 7-20. Figure 7-18 The ARP response. I do and here is my physical address. Reply from C Address Resolution Protocol (ARP)-2 A broadcast Figure 7-19 to all The RARP query. Here is my physical address. RARP Operations Query- 1 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 X.25, Internets, Intranets, and Extranets Figure 7-20 The RARP response. Here is your network address. Server RARP Operations Response-2 IP Addressing Each address assigned to a network is given an IP address consisting of a four-byte address. The addressing mechanisms are controlled by an organi- zation called the Internet Network Information Center (InterNIC). Every Internet address is comprised of a network and a host address. The Inter- NIC assigns a class of network address that is broken down into the fol- lowing classes, as shown in Figure 7-21: Class A addresses use the first 8 bits (the first bit is set to a 0, leaving 7 bits for the network number) of the address for the network number, followed by a 24-bit address for the host. Figure 7-21 Class A IP addressing. Network C