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<html> <head> <meta content="en-us" http-equiv="Content-Language"> <meta content="text/html; charset=UTF-8" http-equiv="Content-Type"> <link type="text/css" rel="stylesheet" href="../../../../../css/ccna.css"> <script src="../../../../../js/framesetHelper.js" language="JavaScript"></script><script language="JavaScript"> window.scrollTo(0,0); function newPage(pageID) { alert("COMMING SOON!!\nThis feature is currently in development."); } function launchMoreInfo(oid) { dash = oid.indexOf('-'); sub1 = oid.substring(0,dash); sub2 = oid.substring(dash+1); // this is an URL base on the // system that generated the static // download of the curriculum. httpref = "http://nomar.sdf.cisco.com/servlet/org.cli.delivery.rendering.servlet.MIServlet/Static=true,LMSID=DTUI,Engine=dynamic,Theme=cnamstheme,Style=ccna,Language=en,Version=2,RootID=knet-v214aCV47051/CHAPID=null/RLOID=null/RIOID=null/"; newref = httpref + sub1 +"/"+ sub2 +"/moreinfoframeset.html"; //alert("new newref :\n" + newref); window.open(newref,'MoreInfo','toolbar=no,status=yes,menubar=no,location=no,scrollbars=yes,height=442,width=756,left=20,top=20,resizable=yes') } function launchContentResource(contentID) { top.currentSupport = 0; 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Routers are Layer 3 devices which determine best path for packets through a network and then switch packets to the port which will lead to their destination network (IP) address.</p> <p>This TI relates to CCNA Certification Exam Objective #7.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>The router operates at the OSI network layer, otherwise known as Layer 3.<img border="0" src="../../../../../CHAPID=knet-v214aCH47503/RLOID=knet-v214aRLO47534/RIOID=knet-v214aRIO121110/knet/v214adataimage4/4.gif" width="12" height="12"> Working at Layer 3 allows the router to make decisions based on network addresses as opposed to individual Layer 2 MAC addresses. Routers can also connect different Layer 2 technologies, such as Ethernet, Token-ring, and FDDI. Because of their ability to route packets based on Layer 3 information, routers have become the backbone of the Internet, running the IP protocol.</p><p>The purpose of a router is to examine the Layer 3 addresses of incoming packets, choose the best path for them through the network, and then switch them to the proper outgoing port. Routers are the most important traffic-regulating devices on large networks. They enable virtually any type of computer to communicate with any other computer anywhere in the world. While performing these basic functions, routers can also execute many other tasks that are covered in later chapters.</p><p>The symbol for a router, with its inward- and outward-pointing arrows, is suggestive of two primary purposes. These two purposes are path selection and switching of packets to the best route.<img border="0" src="../../../../../CHAPID=knet-v214aCH47503/RLOID=knet-v214aRLO47534/RIOID=knet-v214aRIO121110/knet/v214adataimage1/1.gif" width="12" height="12"> A router can have many different types of interface ports. Figure <img border="0" src="../../../../../CHAPID=knet-v214aCH47503/RLOID=knet-v214aRLO47534/RIOID=knet-v214aRIO121110/knet/v214adataimage2/2.gif" width="12" height="12"> shows a serial port, which is a WAN connection. This figure also shows the console port connection, which provides a direct connection to the router for configuration. Figure <img border="0" src="../../../../../CHAPID=knet-v214aCH47503/RLOID=knet-v214aRLO47534/RIOID=knet-v214aRIO121110/knet/v214adataimage3/3.gif" width="12" height="12"> shows another port interface type. The type shown is an Ethernet port, which is a LAN connection. This particular router has both a 10BASE-T and AUI connector for the Ethernet connection.</p><table cellpadding="0" cellspacing="4" width="63%" border="0" xmlns:java="http://xml.apache.org/xslt/java"> <tr> <td valign="middle" width="8%"><img height="23" width="23" src="../../../../../images/ccna/common/icon2.gif"></td><td valign="middle" width="92%"><span class="cstitle">Web Links</span></td> </tr> <tr> <td valign="middle" width="8%"> </td><td valign="middle" width="92%"><span class="smtext"><a target="_blank" href="http://www.cisco.com/">Cisco Systems</a></span></td> </tr> </table></td> </tr> </table> </td> </tr></table> <p> </p> <table width="100%" cellspacing="0" cellpadding="2" border="0" valign="bottom"> <tr> <td></td> </tr> </table> </body></html>⌨️ 快捷键说明
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