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<h2><a href="/message/3751318#3751318">Configuring the
ARP cache timeout for Cisco phones</a></h2></div></div>
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<p>Hi All,</p>
<p style="padding-bottom:0px;padding-left:0px;padding-right:0px;height:8pt;padding-top:0px;"> </p>
<p>I am hoping to configure the ARP cache timeout for Cisco phones using the
dhcp option.</p>
<p>I was wondering if anyone here has done it or can verify that this would be
correct.</p>
<p style="padding-bottom:0px;padding-left:0px;padding-right:0px;height:8pt;padding-top:0px;"> </p>
<p>Say for example I have a DHCP pool named VOICE.</p>
<p>In this network, the CUCM is located at IP address 10.2.200.110 </p>
<p style="padding-bottom:0px;padding-left:0px;padding-right:0px;height:8pt;padding-top:0px;"> </p>
<p>I did some google searching and found a Wiki site with the various dhcp
options defined in it.</p>
<p style="padding-bottom:0px;padding-left:0px;padding-right:0px;height:8pt;padding-top:0px;"> </p>
<p><a class="jive-link-external-small" href="http://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol">http://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol</a></p>
<p>According to the site, dhcp option 35 is used as the ARP Cache Timeout value
and it is 4 bytes long.</p>
<p style="padding-bottom:0px;padding-left:0px;padding-right:0px;height:8pt;padding-top:0px;"> </p>
<p>Lets say that I would like to set my arp cache timeout to be 300 seconds.</p>
<p>I convert 300 to hex and get 12C.</p>
<p>Since my field will need to be four bytes long this becomes 0000.012C.</p>
<p style="padding-bottom:0px;padding-left:0px;padding-right:0px;height:8pt;padding-top:0px;"> </p>
<p>I think that the following dhcp pool will provide 300 seconds for the phone
ARP cache timeout.</p>
<p style="padding-bottom:0px;padding-left:0px;padding-right:0px;height:8pt;padding-top:0px;"> </p>
<p>ip dhcp pool VOICE</p>
<p>network 10.240.1.0 255.255.255.0</p>
<p>default-router 10.240.1.1</p>
<p>option 150 ip 10.2.200.110</p>
<p>option 35 hex 0000.0c12 </p>
<p style="padding-bottom:0px;padding-left:0px;padding-right:0px;height:8pt;padding-top:0px;"> </p>
<p>Can anyone help me out with a verification or point me in the direction of
the appropiate documentation?</p>
<p style="padding-bottom:0px;padding-left:0px;padding-right:0px;height:8pt;padding-top:0px;"> </p>
<p>Many thanks for any assistance.</p>
<p style="padding-bottom:0px;padding-left:0px;padding-right:0px;height:8pt;padding-top:0px;"> </p>
<p>Regards</p>
<p style="padding-bottom:0px;padding-left:0px;padding-right:0px;height:8pt;padding-top:0px;"> </p>
<p>Amanda Lalli-Cafini</p></div>
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