DHCP errors with Cisco phones

[Jonnyballgame34]

Greetings,

I'm having problems with a LAN that's running a 3850 as the core and 2960's as the access layer switches.  I have IP phones set up for DHCP, sometimes they will pick up DHCP addresses, and sometimes they won't.  I doesn't help that the site is remote and when the dhcp doesnt' work the local person sticks a static on there.   But my pool looks like this

Pool VOICE-VLAN306 :
Utilization mark (high/low) : 100 / 0
Subnet size (first/next) : 0 / 0
Total addresses : 126
Leased addresses : 89
Excluded addresses : 1
Pending event : none
1 subnet is currently in the pool :
Current index IP address range Leased/Excluded/Total
10.87.194.251 10.87.194.129 - 10.87.194.254 89 / 1 / 126

 About 100 addresses are actually being used, (The exclusions aren't showing now because I just cleared the conflicts).   Is there any none error with this?  I have 1 other /25 dhcp pool that has around 100 users on it, (not for phones), and I don't run into dhcp issues there.

also, in the past, I've had them remove all the statics, reboot the phones on dhcp, and again sometimes they work, sometimes they don't. And it starts the cycle over, he starts putting statics on---creating exlclusions...etc.

Are there any know bugs on this?  I'm about 75-80% utilization the scope, but even when it's below 70% I see this problem. 

Thansk

[Julio E. Moisa]

Hi

The Cisco phones use CDP procotol to communicate with the DHCP server, have you disable CDP on the switch or some device? 

I have users connected to switches 3850 without any DHCP problem, have you checked the parameters configured on the DHCP server as well?

[Jonnyballgame34]

thanks for taking the time to look at my question.  CDP is enabled...these don't connect to the core, the go through the access switches.  

[Julio E. Moisa]

Thanks, can we discard ip dhcp snooping configured?

[Jonnyballgame34]

Good question---I will look and reply..thanks!

[Julio E. Moisa · Accepted solution]

You are welcome, please keep me posted.

:-)

[Jonnyballgame34]

HI, 

Thanks again for your help with this.  A change in the DHCP timeout resolved it.  The timeout was set to the standard that works at all our other locations, but this particular site has lots of reliability issues with the WAN circuit.  So apparently they were dropping constantly trying to renew, and hitting exclusions.  And by the time I'd get to look at it the leases would have ended and I wouldn't see the problme. Thanks again for your help. 

[Julio E. Moisa]

Thank you so much Jon for the update.

Have a good day

:-)

[Jonnyballgame34]

no snooping....and they are spread out across the access switches.  

[Julio E. Moisa]

Thanks, can you share the config of the 3850 and 2960?

[Leo Laohoo]

Post the config of the DHCP scope.  Cisco VoIP units require DHCP Option 150.