📄 arptheory.htm

📁 BOSON NETSIM是目前最好的路由器模拟软件
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<p><b><font size="4" color="#008000" face="Arial">ARP Overview</font></b></p>
<p><font face="Arial, Arial, Helvetica">In this lab you will view the ARP table
that is stored in the router. You will also learn how to clear the router's
table as a troubleshooting technique.&nbsp; The router stores detailed
information obtained from other devices on the network.&nbsp; The information it
collects is what is referred to as a MAC address and IP address. This
information can get corrupted from time to time which will cause the router to
have packet-delivery problems.&nbsp; When this happens we must clear the ARP
table and have it rebuilt.</font></p>
<p>&nbsp;</p>
<p><font face="Arial, Arial, Helvetica">You can view the ARP table using the
command </font><font face="Terminal" size="2">show arp</font><font face="Arial, Arial, Helvetica">.&nbsp; This displays detailed
information about interfaces that are learning MAC addresses.&nbsp; Looking at
the table below we can see that we learn the IP address and MAC (hardware)
address of each Ethernet interface.&nbsp; The age is how long we have had the
information and the interface is what interface we learned this information
from.&nbsp;<br>
Notice the age time on the 1.1.1.4 address, this is because it is the IP address
of the Ethernet port that is connected to the router.</font></p>
<p><font face="Terminal" size="2">eRouter#show arp<br>
Protocol  Address&nbsp;&nbsp;&nbsp;&nbsp; Age (min)&nbsp;&nbsp; Hardware&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Addr&nbsp;&nbsp;&nbsp;&nbsp; Type   Interface<br>
Internet  1.1.1.2&nbsp;&nbsp;&nbsp;&nbsp; 207&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
0000.0c32.f57d&nbsp;&nbsp;&nbsp;&nbsp; ARPA&nbsp;&nbsp;&nbsp;&nbsp; Ethernet0<br>
Internet  1.1.1.4&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
0060.7062.e040&nbsp;&nbsp;&nbsp;&nbsp; ARPA&nbsp;&nbsp;&nbsp;&nbsp; Ethernet0<br>
eRouter#</font></p>
<p><font face="Arial">You must be in privileged mode to clear the ARP table.&nbsp; After entering
privileged mode the command to clear the ARP table is </font>
<font face="Terminal" size="2">clear
arp</font><font face="Arial">. After you have cleared the ARP table you can view 
it again using the </font><font face="Terminal" size="2">show arp</font><font face="Arial"> 
command. Notice all the entries have disappeared with the exception of the 
directly connected interfaces of the router.</font></p>
<p><font face="Terminal" size="2">eRouter#show arp<br>
Protocol  Address          Age (min)  Hardware Addr   Type   Interface<br>
Internet  1.1.1.2                 -   0060.7062.e040 ARPA   Ethernet0<br>
eRouter#</font></p>
<p>&nbsp;</p>

<p><font face="Arial" size="2"><span class="724482219-24092001">Copyright (c) 
1998-2003 Boson Software, Inc.&nbsp; All Rights Reserved.</span></font></p>

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