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Cisco 7970 phone unregisters


A few of our 7970 cisco phones unregister when DHCP leases expires and takes a few minutes to renew the new IP address. We have call manager 8.5 is there a setting on the phone that would prevent the 7970 phone from unregister for so long or some command that needs to be configure on 3750 switch where the phone is connnected?


No, there is no setting on

No, there is no setting on the phone for this. 


Where are you running the DHCP server?  Is it on an IOS device?  On the CUCM server?  Somewhere else?  What is your lease time set to? 


Generally on a device like a phone, you'd set the least time out somewhere between 7 and 30 days.  They don't move around much.  Once half the lease lifetime is expired, they will start attempting to renew the lease.  If your phones are dropping out, they aren't able to renew the lease.  Could be for any number of reasons. 


Best practice is not to run DHCP on the CUCM server.  It should be fine if you want to do it on the 3750 or a router (or even a Microsoft or Linux server in your environment if you prefer).  But if it's already on a device of that type, you may have some underlying issues in your R/S infrastructure.




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