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

[Amanda Lalli-Cafini]

Hi All,

 

Thanks very much

I will arrange a packet capture as a baseline, but we are running the phones
in a /23 subnet that is also used by CUCM.

 

Regards

 

Amanda

 

 

http://www.youtube.com./watch?v=8eluIEjFCvE&feature=channel&list=UL

 

From: Ryan Ratliff [mailto:rratliff at cisco.com] 
Sent: Tuesday, 9 October 2012 10:14 PM
To: David Sullivan
Cc: Amanda Lalli-Cafini; cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] setting the ARP cache timeout for phones using
DHCP option

 

I'd agree with both Justin and David.  People use /24s for their voice vlans
all the time and never run into arp cache issues on the phones.   

 

You need to get a packet capture to see what is really happening.  If your
CUCM is really on a different subnet than the phone then the arp cache entry
for the default gateway (that let's the phone stay registered with CUCM)
will be the same one needed for the phone to respond to a ping from the same
router.  

 

-Ryan 

 

On Oct 9, 2012, at 4:21 AM, David Sullivan
<David.Sullivan at barnetsouthgate.ac.uk> wrote:

 

I have seen this issue and it was related to the mac address table timeout
being shorter than the arp timeout, on switches I normally match the two
with:

mac address-table aging-time 14400

This timeout being far easier to change than changing the arp settings on
every device, the re-arp will then refresh the mac address table.

David.

* Barnet and Southgate College is a highly successful Further Education
college with around 21,000 students of all ages from 14 years upwards. 

* The College occupies four main campuses: Grahame Park at Colindale,
Southgate, Edmonton Green and the brand new town centre campus at Wood St,
High Barnet. 

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