[cisco-voip] setting the ARP cache timeout for phones using DHCP option

[Ryan Ratliff]

CSCtf62463 seems to indicate the 9971 phones don't support DHCP option 35.  This will vary by model so YMMV.

-Ryan

On Oct 8, 2012, at 4:10 AM, alalli at iinet.net.au wrote:

Currently Being Moderated
Configuring the ARP cache timeout for Cisco phones

Hi All,

 
I am hoping to configure the ARP cache timeout for Cisco phones using the dhcp option.

I was wondering if anyone here has done it or can verify that this would be correct.

 
Say for example I have a DHCP pool named VOICE.

In this network, the CUCM is located at IP address 10.2.200.110

 
I did some google searching and found a Wiki site with the various dhcp options defined in it.

 
http://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol

According to the site, dhcp option 35 is used as the ARP Cache Timeout value and it is 4 bytes long.

 
Lets say that I would like to set my arp cache timeout to be 300 seconds.

I convert 300 to hex and get 12C.

Since my field will need to be four bytes long this becomes 0000.012C.

 
I think that the following dhcp pool will provide 300 seconds for the phone ARP cache timeout.

 
ip dhcp pool VOICE

network 10.240.1.0 255.255.255.0

default-router 10.240.1.1

option 150 ip 10.2.200.110

option 35 hex 0000.0c12          

 
Can anyone help me out with a verification or point me in the direction of the appropiate documentation?

 
Many thanks for any assistance.

 
Regards

 
Amanda Lalli-Cafini

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