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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">8.1</td><td width="100%" class="rlohdr"> <table width="90%" cellpadding="0" cellspacing="0" border="0"> <tr> <td class="rlohdr">Basic Network Design and Documentation</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">8.1.1</td><td width="100%" class="riohdr"> <table width="90%" cellpadding="0" cellspacing="0" border="0"> <tr> <td class="riohdr">General design process</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 present an overview of Layer 1, 2, and 3 design issues. The actual design activities in the semester 1 project in chapters 8 and 9 are primarily Layer 1 issues. Layer 2 and Layer 3 design issues are paramount in the Threaded Case Study in semester 3. First, a Layer 1 topology is decided upon. This is the part of the design process the students will be implementing in their structured cabling project. The process continues on, adding a Layer 2 topology (primarily switching) to the Layer 1 topology. Finally, a Layer 3 topology, such as a network layer addressing scheme, would be implemented. The Layer 3 topology also involves the placement of routers for segmentation of collision domains, segmentation of broadcast domains, and connection to WAN links. Again, the emphasis for the students should be on contextualizing their structured cabling project within the OSI model.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>This lesson includes a comprehensive list of the steps to be followed in order to design a network. Not all of these steps will be taken when the structured cabling project is done in this chapter. Many of the decisions have already been made by the existing network design and network administrator. However this is the process that will eventually be followed.</p><p>The network design completed in this chapter could take into consideration many technologies such as Token Ring, FDDI, and Ethernet. This design will focus on the Ethernet technology since it is the technology that students are most likely to encounter when planning future designs. Ethernet has a logical bus topology, which leads to collision domains. Try to keep these collision domains small by using the process called segmentation. Once settling on Ethernet, a Layer 1 LAN topology must be developed. The type of cabling and the physical topology (wiring) must be determined. The most common choice is CAT 5 UTP as the medium with an extended star topology as the physical topology. The type of Ethernet topology that will be used must be selected. Two common types of Ethernet are 10BASE-T and 100BASE-TX (Fast Ethernet). If adequate resources exist, 100BASE-TX could be run throughout the network. If not, Fast Ethernet could be used to connect the main distribution facility (central control point of our network) to other intermediate distribution facilities. Hubs, repeaters, and transceivers could be used in the design, along with other Layer 1 components such as plugs, cable, jacks, and patch panels. To finish Layer 1 design, both a logical and a physical topology must be generated. </p><table cellpadding="0" cellspacing="0" border="0"> <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="3" border="0"> <tr> <td><span class="note"><b>NOTE:</b><p>As always, an important part of the design involves documenting all work.</p></span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>The next step is to develop a Layer 2 LAN topology by adding Layer 2 devices to the topology to improve its capabilities. Switches could be added to reduce congestion and collision domain size. In the future it may be affordable to replace hubs with switches, and other less intelligent Layer 1 devices with more intelligent Layer 2 devices.</p><p>The next step is to develop a Layer 3 topology. This means adding Layer 3 devices that expand the capabilities of the topology. Layer 3 is where routing is implemented. Routers could be used to build scalable internetworks such as LANs, WANs, or networks of networks. Routers will impose logical structure on the network being designed. They can also be used for segmentation. Routers, unlike bridges, switches, and hubs, break up both collision and broadcast domains.</p><p>The network design should also consider the placement of such things as file servers, databases, and other shared resources. The LAN link to WANs and to the Internet should also be considered. Finally, the physical and logical topologies of the network design should be documented. Any brainstormed ideas, problem-solving matrices, and any other notes made while making the determinations should be documented as well.</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.siemon.com/glossary/definitions.html">Cabling Glossary</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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