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Frequent Contributor


Hello Everyone,

I know we cannot have more than one DHCP server configured in a CUCM cluster but how many IP address a CUCM DHCP server can handle? 

40000 IP Phones can be registered in a cluster and 7500 in a single CUCM server.

Is that a fair statement to say a CUCM DHCP server can handle a minimum of 7500 IP Addresses? The SRND recommends to use dedicated DHCP server for networks larger than1000 phones. Could that dedicated DHCP server be a CUCM server? If so what would happen in case of having a network with 30000 IP Phones? Can we have multiple CUCM DHCP servers?

In case of using a Windows DHCP server, do we need to have two dedicated DHCP servers for Voice & Data? Can a single DHCP server serve both Data & Voice networks?






Threr're bunch of things you need to verify:

1) Does the CSS of the Cisco IP Phone allow to call the grand system phones? Your Cisco IP Phone CSS needs to include the partition of the grand system phones.


2) Do you have a route pattern which includes the extensions of the grand systems's phones?

 -  Creat a route group and associate it with the trunk you created in the CUCM

 -  Create a route list and associate it with the route group you just created

 - Create a route pattern which contains the extensions of the grand system phones. Lets say the extension in grand system are btw 7000-7999. You need to create a route pattern 7xxx and select the trunk you created as the Gateway/Route list 

You can use Dialed Number Analyzer to see if you have a route to grand system phones:

Go to Cisco Unified Serviceability -> Tools -> Dialed Number Analyzer


Good luck,






Hi mightykind,

many many thanks for your reply,

i have tried it and in DNA, the result is like "RouteThisPattern" , but while i am trying to make a call from 2001 (cisco phone) to 1003 (grand stream phone) call is not getting placed.

Actually there is a thing that i missed to explain you in the previous explained architecture.
The calling from Grand stream phones to cisco phones is not processed directly...., but that calling from grandstream phone to cisco phone is happening through a customercare application.

in that customercare application we can make a call to outside mobile network, then the customer's call can be transferred to the Cisco phone through that application only....

So my doubt is.., the call getting transferred only through customercare application, then will i be able to make a call directly from cisco phones to grandstream phone?

so i have talked to that IP-PBX vendors. He told that he is not getting any hit from my cucm side, while trying to make a call to 1001 ( grand stream phone ).

so, as he is not getting the call placed, he told me that the call processing can be made in two ways 1) SIP trunk 2) peer to peer. So he told to do it in the other way.(peer solution)
He gave me "peer no" , "password" , "IP", "SIP port no".

SO how to configure this peer to peer on CUCM now.

Thanks & Regards
Sai Bhuwan



there is second thread with the same your explaining. As per the rules, please follow single thread so as the team can help you through resolution.


Duplicate thread here 


Ritesh Desai

Please rate helpfull post.

*** Please rate helpful post. Please mark as answer if it solves your problem/query.
regards, Ritesh Desai

Are you able to ping the romote IP-PBX from your CUCM.

From CLI:

utils network ping "IP address of the remote PBX"





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