[cisco-voip] IP phone DHCP question or two

[Lelio Fulgenzi]

some general comments: 

    • in v7.1, to bulk reset phones: 


        • Bulk Administration > Phones > Reset/Restart Phones > Query [or Custom File] 
    • 
I support the idea of lowering the lease time, worse comes to worse, if the process fails for a group of phones, minimally they'll try to grab a new lease themselves. I would suggest a lease time of about 30 to 60 min, any less might be hard on the router while you wait out the lease times of existing leases     • I am pretty sure when a phone can no longer communicate with it's DHCP server, it will issue a broadcast request and start the process all over again, it won't ask to use it's current IP address from the new server. 
    • I am also pretty sure that the phones will only go into broadcast mode when they can't communicate with the original DHCP server. The phone tries for a while before it reverts to trying from scratch, i.e. broadcast mode. 
    • Be ready for some IP address conflicts, it's inevitable. However, you should be able to minimize them with the steps above. Even with conflicts, the phones will reboot and get new IP addresses so they'll take care of themselves. 





Like others have said, test with on VLAN first and document the steps and/or behaviour, that way you can plan the mass move. 




We did something like this and it was pretty painless after everything was planned out. 

--- 
Lelio Fulgenzi, B.A. 
Senior Analyst (CCS) * University of Guelph * Guelph, Ontario N1G 2W1 
(519) 824-4120 x56354 (519) 767-1060 FAX (ANNU) 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
Cooking with unix is easy. You just sed it and forget it. 
- LFJ (with apologies to Mr. Popeil) 


----- Original Message -----
From: "Tim Reimers" <treimers at ashevillenc.gov> 
To: cisco-voip at puck.nether.net 
Sent: Wednesday, February 1, 2012 5:30:50 PM 
Subject: [cisco-voip] IP phone DHCP question or two 




Hi all – 



What are all the options for forcing an IP phone to get a new IP address? 



I know of: 

- Resetting it (I think) (how does one globally reset all phones in UCM?) 

- shut/no shut the port 

- int range (whatever to whatever) and inline power never/inline power auto 



I want to switch from Cisco router based DHCP to Microsoft DHCP 





My plan would be: 

Disable the ip dhcp pool on the cisco router for a given Vlan/subnet 

Enable the ip helper addresses 

Restart the phones and they would pull IP addresses from the new DHCP server. 



I know Microsoft devices (aka XP, win7 workstations) tend to know their old IP and will sometimes cause an IP conflict when changing DHCP servers, 

even if you reboot them they sometimes conflict. 



Do Cisco IP phones have that same problem, or once they reset do they forget all about any IP they once had, and go get a new one from the DHCP server 

(obviously, if the DHCP server has a lease for the phone, it gets the same IP back, but that’s not the phone’s doing..) 



thanks, Tim 
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