[c-nsp] dhcp problems with ip phones

Heath Jones hj1980 at gmail.com
Wed Oct 6 14:19:34 EDT 2010


> After this the endpoint sends an gratuitous arp on the requested address, and then an other answers that it has the ip address.
How are you seeing this behaviour - packet capture or does the
endpoint report it?

> I've pulled out the arp table before enabling a new endpoint to get the ip address list on the switch.
> But after the decline I can't find the mac address in the arp table that I pull out before activating the new endpoint.
Unless the switch itself has 'talked' with the first endpoint, it
won't be in the arp table. It will be in the switch table though.

You could perform this to figure out where the problem lies:
1) Plug in endpoint. Let it go off and get an IP address, and then
detect the duplicate, making a note of the IP address that was
assigned.
2) Unplug endpoint.
3) Ping IP from switch.
5) Look up switch ARP table, and mac address tables.


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