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</script> </head> <body onLoad="window.focus();" alink="#000000" vlink="#000000" link="#000000" bgcolor="#E7E7E7" background="../../../../../images/ccna/common/bg.gif"> <table width="100%" cellspacing="0" cellpadding="2" border="0"><tr> <td bgcolor="#000000"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td class="rlohdr"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td valign="top" class="rlohdr">3.1</td><td width="100%" class="rlohdr"> <table width="90%" cellpadding="0" cellspacing="0" border="0"> <tr> <td class="rlohdr">Basic LAN Devices</td> </tr> </table> </td> </tr> <tr> <td bgcolor="#000000"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td class="riohdr"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td valign="top" class="riohdr">3.1.11</td><td width="100%" class="riohdr"> <table width="90%" cellpadding="0" cellspacing="0" border="0"> <tr> <td class="riohdr">Network segments</td> </tr> </table> </td> </tr> <tr> <td colspan="4"> <table width="90%" cellspacing="0" cellpadding="0" border="0"> <tr> <td class="smtext"> <p> </p><table cellpadding="0" cellspacing="0" width="100%" border="0" xmlns:java="http://xml.apache.org/xslt/java"> <tr> <td width="100%"><img height="10" width="1" border="0" src="../../../../../images/ccna/common/transdot.gif"></td> </tr> <tr> <td width="100%"> <table bgcolor="#000000" bordercolor="#000000" cellspacing="0" bordercolorlight="#000000" width="100%" border="0"> <tr> <td width="100%"> <table bgcolor="#FFFFFF" cellspacing="0" cellpadding="2" width="100%" border="0"> <tr> <td valign="middle"><img height="22" width="22" border="0" src="../../../../../images/ccna/common/inotes.gif"></td><td valign="middle"><span class="cstitle">Instructor Note</span></td> </tr> <tr> <td valign="top"> </td><td valign="top"><span class="cstext"> <p>The purpose of this target indicator is to allow the student to start recognizing network segments on a logical topology, to describe how they really appear, and to briefly describe their function.</p> <p>A good class activity is to make flash cards -- with the device symbol on the front, and the device name, layer, and function on the back. Network segments refer to regions of the internetwork that act as one network for collisions and broadcasts. Note that the word network segment is rather sloppily used. Some use it to indicate any section of media between two networking devices. We recommend restricting of the use of "segment" to mean the section of a network bounded by bridges and switches [a single collision domain] and by routers [a single broadcast domain].</p> <p>This TI relates to CCNA Certification Exam Objective #46.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>The term <i>segment</i> has many meanings in networking and the correct definition depends upon the situation in which it is used. Historically, a segment identifies the Layer 1 media that provide the common path for data transmission in a LAN. As previously mentioned on the media page, there is a maximum length for data transmission on each type of media. Each time a Layer 2 or Layer 3 device is used to extend the length or manage data on the media a new segment is created.<img border="0" src="../../../../../CHAPID=knet-v214aCH47503/RLOID=knet-v214aRLO47534/RIOID=knet-v214aRIO121112/knet/v214adataimage1/1.gif" width="12" height="12"><img border="0" src="../../../../../CHAPID=knet-v214aCH47503/RLOID=knet-v214aRLO47534/RIOID=knet-v214aRIO121112/knet/v214adataimage2/2.gif" width="12" height="12"> The devices that are used to create new segments are covered in the rest of the pages of this chapter.</p><p>Some people refer to segments by the term wires, though the "wire" might be optical fiber, wireless medium, or copper wire. The function of the different segments of a network is to act as efficient LANs that are part of a larger network.</p><p>Other definitions of the term segment are commonly used in networking. Here are two other definitions that will be used in later networking topics. It is important to note that since these topics will be covered later, you may not understand what they mean right now. The only reason that this is discussed here is to eliminate confusion later when the term <i>segment</i> has a different network meaning.</p><p>Cisco commonly defines a segment as a collision domain. The small difference between the first and second definitions will be explained in a later chapter when collision domains are discussed.</p><p>Finally, a third definition for segment that you will learn describes a Layer 4 PDU (Protocol Data Unit). This definition again will be covered in later chapters.</p><table cellpadding="0" cellspacing="0" width="100%" border="0" xmlns:java="http://xml.apache.org/xslt/java"> <tr> <td width="100%"><img height="10" width="1" border="0" src="../../../../../images/ccna/common/transdot.gif"></td> </tr> <tr> <td width="100%"> <table bgcolor="#000000" bordercolor="#000000" cellspacing="0" bordercolorlight="#000000" width="100%" border="0"> <tr> <td width="100%"> <table bgcolor="#FFFFFF" width="100%" cellspacing="0" cellpadding="0" border="0"> <tr> <td> <table bgcolor="#FFFFFF" cellpadding="2" width="100%" border="0"> <tr> <td valign="top"><img height="22" width="22" border="0" src="../../../../../images/ccna/common/icon10.gif"></td><td valign="middle"><span class="cstitle"><a href="#" onClick="window.open('../../../../../CHAPID=null/RLOID=null/RIOID=knet-v214aRIOv2141001/knet/v214aRIOv2141001/iaactivity.html','LabActivity','width=742,height=390,toolbar=0,scrollbars=0,left=26,top=38');void(null);">Interactive Lab Activity</a></span></td> </tr> <tr> <td valign="top"> </td><td valign="top"><span class="cstext"> <p>As a network administrator, you may have the opportunity to decide which physical topology to use in your local area network. You should be familiar with the most common topologies and the devices used in the network.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table> </td> </tr> </table> <p xmlns:java="http://xml.apache.org/xslt/java"> </p></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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