tailieunhanh - CompTIA Network+ Certification Study Guide part 77

CompTIA’s Network+ certification Study Guide part 77 is a globally-recognized, vendor neutral exam that has helped over 235,000 IT professionals reach further and higher in their careers. The 2009 Network+ exam (N10-004) is a major update with more focus on security and wireless aspects of networking. Our new study guide has been updated accordingly with focus on network, systems, and WAN security and complete coverage of today’s wireless networking standards. | 746 Appendix C 15. Over the weekend you have installed a new NIC in a server and have configured the NIC to have the same static IP address that was set on the old NIC. First thing Monday morning you receive a network alert that there is large number of broadcasts taking place on the network segment where this server resides. What is the probable cause for the increase in broadcasts A. ARP resolutions B. RARP resolutions C. DNS resolutions D. Dig attempts Correct answers and explanations A. Answer A is correct because by replacing the NIC in the server the IP address to MAC address information that was cached on other machines for that server is now out of date. In order to communicate with the server successfully the other machines will perform an ARP broadcast requesting the MAC address that corresponds to the server s IP address. Since the replacement took place over the weekend when it was likely that many machines were off or not in use the spike in broadcasts was not seen until Monday morning when the machines were powered on and attempting connection to the server. The ARP broadcasting will subside once resolution has occurred and the machines are able to store the new MAC and IP address values in their ARP cache. Incorrect answers and explanations B C and D. Answer B is incorrect because RARP is reverse ARP and in this case it is unlikely that it is being required to connect. The name and the IP address of the server did not change so DNS and other name resolution systems would have the correct information. So once the name resolution has taken place to provide an IP address the final component to retrieve is the MAC address that corresponds to the IP address. ARP is responsible for mapping IP addresses to MAC addresses not RARP. RARP maps MAC addresses to IP addresses. Answer C is incorrect because DNS resolution does not occur over a broadcast. DNS resolution is directed traffic sent to the DNS server. Answer D is incorrect because Dig attempts do not .