[cisco-voip] DHCP and Cisco Phones

[Lelio Fulgenzi]

Because the phones have successfully registered at least once and have downloaded their config, they continue to use that config if they can not communicate to the TFTP server on successful restarts. 

I believe that is the case. Either that or upon failure to retrieve the the TFTP server info from the data vlan DHCP box they revert to the previous TFTP server and download the config again. 

Or, perhaps your data vlan DHCP box is in fact distributing the proper TFTP server. 

Regardless, I would double check your campus security plan. I'm not sure you want a phone that plugs into your data VLAN allowed to register to your voice system. That means just about any data device can....that's a fairly large security hole in some people's books. 


--- 
Lelio Fulgenzi, B.A. 
Senior Analyst (CCS) * University of Guelph * Guelph, Ontario N1G 2W1 
(519) 824-4120 x56354 (519) 767-1060 FAX (JNHN) 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
"Bad grammar makes me [sic]" - Tshirt 


----- Original Message ----- 
From: "Michael Back" <Michael.Back at nisd.net> 
To: cisco-voip at puck.nether.net 
Sent: Tuesday, September 23, 2008 3:51:40 PM GMT -05:00 US/Canada Eastern 
Subject: [cisco-voip] DHCP and Cisco Phones 

I am trying to get a handle on how DHCP works with the cisco phones. I 
know that you configure option 150 in the scope so that a phone can get 
to TFTP for its config. The reason I am asking is this: we have voice 
and data VLANs each pointing to different servers for DHCP. When our 
phones get unplugged from a switch with a voice VLAN and get plugged 
into a switch without a voice VLAN, they get an address from the wrong 
server, but still register to CallManager. How does that happen? I 
hope this isn't too dumb of a question... 

Thanks. 
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