About Cisco IP phone configuration

[ifthahossain]

Please explain the following command:

1. Router(dhcp-config)#option 150 ip 192.168.1.1

2. Router(config-telephony)#max-ephones 2

3. Router(config-telephony)#max-dn 2

4. relation between max-ephones and max-dn ?

5. Router(config-telephony)#ip source-address 192.168.1.1 port 2000

6. Router(config-telephony)#auto assign 1 to 5

[Roger Kallberg]

1. Option 150 points out the TFTP server(s) the phone gets its configuration from
2. Sets the maximum number of phones that can register to the router 
3. Sets the maximum number of directory numbers that can exist in the router 
4. There is no direct relation between these two. Often you would configure double the number of max-dn to the max-ephone, but this is no hard truth, it’s just common practice 
5. This is the source IP of the CME or SRST service that the router will use
6. Not sure what this is used for. Likely you can Google it

[Nithin Eluvathingal]

1. Router(dhcp-config)#option 150 ip 192.168.1.1:
• It specifies option 150, which is the TFTP (Trivial File Transfer Protocol) server address.  TFTP serves as the conduit through which IP phones retrieve their configuration files, enabling them to successfully register.
• In this case, the TFTP server’s IP address is set to 192.168.1.1.
2. Router(config-telephony)#max-ephones 2:
• It sets the maximum number of ephones (IP phones or endpoints) that can be registered with this router to 2.
• Essentially, it limits the number of phones that can be connected to this router for call processing.
3. Router(config-telephony)#max-dn 2:
• It sets the maximum number of directory numbers (DNs) that can be configured on this router to 2.
4. Relation between max-ephones and max-dn:
• max-ephones limits the total number of physical phones that can register with the router.
• max-dn limits the total number of individual lines/extensions (DNs) that can be configured on a Cisco Unified CME router.
• The maximum you can set depends on the software version, router platform, and amount of memory that you have installed.
5. Router(config-telephony)#ip source-address 192.168.1.1 port 2000:
• It specifies the source IP address and port number  that the Cisco Unified CME router uses for IP phone registration
• In this case, the source IP address is 192.168.1.1, and the port number is 2000.
6. Router(config-telephony)#auto assign 1 to 5:
• This command is related to ephone-DNs (directory numbers)
• It automatically assigns DNs to ephones.
• In this example, it assigns DNs from 1 to 5 to ephones as they register.

[ifthahossain]

Please explain the directory number and why it is necessary for phone configuration. Could you explain it through an example? is there any relation between IP phone and directory number? For if I have 10 IP phones then how many #max-dn and #auto assign do I have to configure by command?

[Maren Mahoney]

The way to think of it is that the phone and the directory number are two discrete and separate objects. Then, as part of the phone configuration, you tell the system which directory number should appear on which button.

Max-ephones is the maximum number of phones that can be registered to the system, and that is limited by licensing. Ditto with max-dn, but since a single phone can have more than one directory number on it, it is common that the max-dn setting ends up higher than the max-phone setting.

As for auto-assign, when that is in place the first phone that registers will automatically be assigned the first (lowest ephone-dn number) directory number and that directory number will be placed on button 1 on that phone. The next phone to register will be assigned the second number and so on. Once the number is assigned that information is saved so the same phone will always have that same number until you, the administrator, changes it.

Maren

[Roger Kallberg]

To add what @Maren Mahoney wrote in her excellent answer you don’t need to use auto assignment for director numbers, you can configure that specifically on each ephone configuration element in the router to control which phone number each phone has.