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<h2 class="first-section-title"><a name="258"></a><a name="ch08lev1sec2"></a>Networking Basics</h2><p class="first-para">The easiest way to explain how networking works is by example. Let's look at what happens when I surf to <a target="_top" class="url" href="http://www.javasoft.com/">http://www.javasoft.com/</a>, the Java technology Web site. My DNS server (63.240.76.4) is asked to provide the IP address for the Java technology Web site, which is 192.18.97.39. My machine sends the request to the gateway/firewall device in my basement (192.168.1.1). That gateway sends the request to my cable modem (IP address unknown). The cable modem sends the request to the gateway provided by my ISP. My communication goes through a large number of routers and gateways illustrated by the traceroute in <a class="internaljump" href="#ch08list01">listing 8.1</a>. Eventually, my request gets to Sun's Java technology Web site.</p>
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<span class="example-title"><span class="example-titlelabel">Listing 8.1: </span>A Traceroute to <a target="_top" class="url" href="http://www.javasoft.com/">http://www.javasoft.com/</a></span><a name="259"></a><a name="ch08list01"></a>
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<td bgcolor="000080" class="bluecell"><font size="2" face="Arial" color="010100"><b><img src="_.gif" width="1" height="2" alt="Start example" border="0"></b></font></td>
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C:\>tracert www.javasoft.com
Tracing route to www.javasoft.com [192.18.97.39]
over a maximum of 30 hops:
1 10 ms 10 ms 10 ms 10.164.160.1
2 10 ms 10 ms 10 ms 12.244.106.129
3 10 ms 10 ms 10 ms 12.244.68.26
4 10 ms 20 ms 10 ms 12.244.68.30
5 10 ms 10 ms 10 ms 12.244.72.242
6 10 ms 20 ms 20 ms gbr2-p100.cgcil.ip.att.net [12.123.5.78]
7 10 ms 20 ms 10 ms tbr1-p013602.cgcil.ip.att.net [12.122.11.37]
8 10 ms 10 ms 10 ms gbr3-p50.cgcil.ip.att.net [12.123.5.146]
9 20 ms 10 ms 10 ms POS5-2.BR5.CHI2.ALTER.NET [204.255.169.145]
10 10 ms 10 ms 20 ms 0.so-3-1-0.XL2.CHI2.ALTER.NET [152.63.71.97]
11 20 ms 10 ms 10 ms 0.so-2-0-0.TL2.CHI2.ALTER.NET [152.63.67.109]
12 20 ms 20 ms 10 ms 0.so-7-0-0.TL2.STL3.ALTER.NET [152.63.146.62]
13 70 ms 70 ms 70 ms 0.so-3-0-0.CL2.DEN4.ALTER.NET [152.63.89.233]
14 71 ms 90 ms 80 ms 178.ATM7-0.GW3.DEN4.ALTER.NET [152.63.72.73]
15 * * * Request timed out.
16 80 ms 70 ms 80 ms rwres.java.Sun.COM [192.18.97.39]
Trace complete.
<a name="260"></a><a name="IDX-103"></a>
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<p class="para">Notice that one of the addresses in the route was unidentifiable and was marked "Request timed out" in the trace. This is probably a firewall. The firewall at the Java technology Web site might not be configured to allow traceroutes initiating from the Internet.</p>
<p class="para">
<a class="internaljump" href="#ch08fig01">Figure 8.1</a> is an example of a network diagram. The lines indicate network connectivity. All machines on the network must be connected to a hub, switch, or router of some type.</p>
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<a name="261"></a><a name="ch08fig01"></a><span class="figuremediaobject"><a href="images/fig119%5F01%5F0%2Ejpg" NAME="IMG_26" target="_parent"><img src="images/fig119_01.jpg" height="407" width="350" alt="Click To expand" border="0"></a></span>
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<span class="figure-title"><span class="figure-titlelabel">Figure 8.1: </span>Network Diagram Example</span>
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