tailieunhanh - CompTIA Network+ Certification Study Guide part 62

CompTIA’s Network+ certification Study Guide part 62 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. | 596 CHAPTER 12 Network Troubleshooting Methodology should be local occurring on the same side of the bridge or switch and no more than 20 percent should cross the bridge or switch. For best performance ensure that those computers that communicate with one another most often are on the same side of the bridge or switch. Frequently accessed file or print servers should be placed on the same side of the bridge or switch as those clients that use them most often. Before implementing a bridging or switching solution you should carefully analyze the normal flow of network traffic and try to group nodes so that most communication and especially transfer of large amounts of data takes place without the need to cross the bridge. Identifying the Cause of an Infrastructure Problem One issue that can sometimes occur with bridges and switches is called looping. This can occur when there is more than one active bridge or switch on a network. In a loop when the bridges and switches don t know the location of a destination computer they send the data frame across the bridge or switch. This results in multiple copies of the same data frame on the network causing unnecessary congestion - but it gets even worse than that. As each device detects the frame sent by the other bridge or switch it passes the frame back across to the other side. The frames coming from the other bridge cause each bridge or switch to make incorrect entries in its routing table for the destination computer and this in turn intermittently prevents the destination computer from receiving data. The problem is intermittent because the bridges keep resetting the entries in the routing table based on where the data frames are coming from. This can go on forever in an endless loop hence the term looping. See Figure for an example of how this can happen. In the scenario shown in Figure if Computer B sends a message to Computer A both bridges would detect the data frame. Neither bridge knows where Computer A