content.html
来自「ccna」· HTML 代码 · 共 246 行
HTML
246 行
<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; dash = contentID.indexOf('-'); sub1 = contentID.substring(0,dash); sub2 = contentID.substring(dash+1); numbackParams = "CHAPID=" + "knet-v214aCH47511" + "/RLOID=" + "knet-v214aRLO47825" + "/RIOID=" + "knet-v214aRIO123692"; ContentRef = "../../../../../"+ numbackParams + "/"+ sub1 +"/"+ sub2 +"/"; eval('parent.frames.content_frame.location.href="'+ContentRef+'content.html"'); eval('parent.frames.media_frame.location.href="'+ContentRef+'media.html"'); eval('parent.frames.navigation_frame.location.href="'+ContentRef+'contentresourcenav.html"'); top.currentSupport++; top.firstSupportPage = contentID; top.prevPage = contentID; top.contentResourceID = contentID; } function launchReference(rioID, rloID, chapterID) { contentID = "knet-v214aCV47051"; dash = contentID.indexOf('-'); sub1 = contentID.substring(0,dash); sub2 = contentID.substring(dash+1); numbackParams = "CHAPID=" + chapterID + "/RLOID=" + rloID + "/RIOID=" + rioID; ContentRef = "../../../../../"+ numbackParams + "/"+ sub1 +"/"+ sub2 +"/"; eval('top.frames.main_frame.location.href="'+ContentRef+'referencecontroller_crf.html"'); chapter = "knet-v214aCH47511"; ch_dash = chapter.indexOf('-'); ch_sub1 = chapter.substring(0,ch_dash); ch_sub2 = chapter.substring(ch_dash+1); params = "CHAPID=" + chapter + "/RLOID=" + "knet-v214aRLO47825" + "/RIOID=" + "knet-v214aRIO123692"; returnRef = "../../../../../"+ params + "/"+ ch_sub1 +"/"+ ch_sub2 +"/pageframeset.html"; top.prevPage = returnRef; } function launchFile(filepath) { newWindow = window.open(filepath,"","top=70,left=120,width="+(screen.width*.50)+",height="+(screen.height*.50)+",resizable=yes,scrollbars=yes,toolbar=yes,menubar=yes,status=yes"); /* if (is.ie && filepath.lastIndexOf(".pdf") != -1) { pageTimer = setInterval("winLoadCheck()", 1000); } */ } function winLoadCheck() { if (newWindow.document.readyState == 'complete') { clearInterval(pageTimer); newWindow.location.reload(); } } // BrowserCheck Object // provides most commonly needed browser checking variables // 19990326 // Copyright (C) 1999 Dan Steinman // Distributed under the terms of the GNU Library General Public License // Available at http://www.dansteinman.com/dynapi/ function BrowserCheck() { var b = navigator.appName if (b=="Netscape") this.b = "ns" else if (b=="Microsoft Internet Explorer") this.b = "ie" else this.b = b this.v = parseInt(navigator.appVersion) this.ns = (this.b=="ns" && this.v>=4) this.ns4 = (this.b=="ns" && this.v==4) this.ns5 = (this.b=="ns" && this.v==5) this.ie = (this.b=="ie" && this.v>=4) this.ie4 = (navigator.userAgent.indexOf('MSIE 4')>0) this.ie5 = (navigator.appVersion.indexOf('MSIE 5.0')>0) this.ie55 = (navigator.appVersion.indexOf('MSIE 5.5')>0) if (this.ie5) this.v = 5 this.min = (this.ns||this.ie) } // automatically create the "is" object is = new BrowserCheck()</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">11.2</td><td width="100%" class="rlohdr"> <table width="90%" cellpadding="0" cellspacing="0" border="0"> <tr> <td class="rlohdr">Network-to-Network Communications</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">11.2.1</td><td width="100%" class="riohdr"> <table width="90%" cellpadding="0" cellspacing="0" border="0"> <tr> <td class="riohdr">Methods for assigning an IP address</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>By now the students have probably been convinced of the importance of IP addresses. But an important question about them has been left unaddressed. How does a host obtain its IP address? Four different methods for obtaining an IP addressed are described.</p> <p>This TI relates to CCNA Certification Exam Objectives #7, #31, and #36.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>After the addressing scheme for a network has been determined, a method must be chosen for assigning addresses to hosts.<img border="0" src="../../../../../CHAPID=knet-v214aCH47511/RLOID=knet-v214aRLO47825/RIOID=knet-v214aRIO123692/knet/v214adataimage1/1.gif" width="12" height="12"> There are essentially two methods for assigning IP addresses. They are <i>static addressing</i> and <i>dynamic addressing</i>. Regardless of which addressing scheme is chosen, no two devices can have the same IP address.</p><p> <b>Static Addressing</b> <br>If IP addresses are assigned statically, each individual device must be configured with an IP address. This method requires keeping very meticulous records, because problems can occur on the network if duplicate IP addresses are used. Some operating systems, such as Windows 95 and Windows NT, send an ARP request to check for a duplicate IP address when they attempt to initialize TCP/IP. If they discover a duplicate, the operating systems will not initialize TCP/IP and will generate an error message. Record keeping is important too, because not all operating systems identify duplicate IP addresses.</p><p> <b>Dynamic Addressing</b> <br>There are a few different methods that can be used to assign IP addresses dynamically. Examples of these are:</p><ul type="disc"><li> <b>Reverse Address Resolution Protocol (RARP)</b> <br> <i>Reverse address resolution protocol (RARP)</i> binds MAC addresses to IP addresses. This binding allows some network devices to encapsulate data before sending them out on the network. A network device such as a diskless workstation might know its MAC address, but not its IP address. Devices using RARP require that a RARP server be present on the network to answer RARP requests.<p>As an example, a source device wants to send data to another device. In this example the source knows its own MAC address, but is unable to locate its own IP address in its ARP table. In order for the destination device to retrieve the data, pass it to higher layers of the OSI model, and respond to the originating device, the source must include both its MAC address and IP address. Therefore, the source initiates a process called a RARP request, which helps detect its own IP address. The device builds a RARP request packet and sends it out on the network. To ensure that all devices see the RARP request on the network, an IP broadcast address is used.</p><p>RARP uses the same packet format as ARP. But in a RARP request, the MAC headers, IP headers, and "operation code" are different from an ARP request. The RARP packet format contains places for MAC addresses of both destination and source. The source IP address field is empty. The broadcast goes to all devices on the network. Therefore, the destination IP address will be set to all binary 1s. Workstations running RARP have codes in ROM that direct them to start the RARP process, and locate the RARP server.<img border="0" src="../../../../../CHAPID=knet-v214aCH47511/RLOID=knet-v214aRLO47825/RIOID=knet-v214aRIO123692/knet/v214adataimage2/2.gif" width="12" height="12"></p> </li><li> <b>BOOTstrap Protocol (BOOTP)</b> <br> A device uses <i>BOOTstrap protocol (BOOTP)</i> when it starts up, to obtain an IP address. BOOTP uses UDP to carry messages. The UDP message is encapsulated in an IP datagram. A computer uses BOOTP to send a broadcast IP datagram (using a destination IP address of all 1s, 255.255.255.255). A BOOTP server receives the broadcast and then sends a broadcast. The client receives a datagram and checks the MAC address. If it finds its own MAC address in the destination address field, then it takes the IP address in that datagram. Like RARP, BOOTP operates in a client-server environment, and only requires a single packet exchange. However, unlike RARP, which only sends back a 4 octet IP address, BOOTP datagrams can include the IP address, the address of a router (default gateway), the address of a server, and a vendor-specific field. One of the problems with BOOTP is that it was not designed to provide dynamic address assignment. With BOOTP a configuration file that specifies the parameters for each device must be created. </li><li> <b>Dynamic Host Configuration Protocol (DHCP)</b> <br><i>Dynamic host configuration protocol (DHCP)</i> has been proposed as a successor to BOOTP. Unlike BOOTP, DHCP allows a host to obtain an IP address quickly and dynamically. All that is required using DHCP is a defined range of IP addresses on a DHCP server. As hosts come online they contact the DHCP server and request an address. The DHCP server chooses an address and allocates it to that host. With DHCP, the entire computer's configuration can be obtained in one message (for example along with the IP address, the server can also send a subnet mask, default gateway, DNS server and other TCP/IP configuration settings).</li></ul></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
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?