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Community Member

IP Phones and DHCP Addresses

I am tasked to expand the size of an IP Phones subnet to accomodate additional phones.

I made the nessasary changes to the DHCP scope config, and rebooted the existing phones.

The phones seem to revert to their original IP address even after a power cycle!!!

If I manually release the DHCP address a new one is obtained correctly. However this is not practical with a large number of phones.

Has anyone else experienced this or know of a solution???

Thanks in advance.


Community Member

Re: IP Phones and DHCP Addresses

The phone "wanting" it's old address is normal behavior for IP phones. Instead of doing a hard reset on the phone, you can "lock-out" the IP address in the DHCP scope, then tell the phone to reset. It'll sort itself out once it realizes it can't have it's old address. You can then unlock the old IP address.

Cisco Employee

Re: IP Phones and DHCP Addresses

Ip phones are not much different when they are DHCP clients.

If the hosts are set to have a lease of 8 days, then at 50% of their lease or 4 days, they will contact the DHCP to renew the lease.

Per MS help file:

You can delete the lease of any DHCP client in the scope. The main reason for doing so is to remove a lease that conflicts with an IP address exclusion or a client reservation that you want to add. Deleting a lease has the same effect as if the client lease expired: the next time that client computer starts, it must enter the initialization state and obtain new TCP/IP configuration information from a DHCP server. There is nothing, however, to prevent the client from obtaining a new lease for the same IP address. You must make the address unavailable before the client requests another lease.

H. M.

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