In Cisco Unified Communications Manager Administration, use the System > DHCP > DHCP Server menu path to configure a DHCP server.
Dynamic Host Configuration Protocol (DHCP) server enables Cisco Unified IP Phones, connected to either the customer's data or voice Ethernet network, to dynamically obtain their IP addresses and configuration information. DHCP uses Domain Name System (DNS) to resolve host names both within and outside the cluster.
DHCP server deletion
If the DHCP server is not in use, Cisco Unified Communications Manager allows you to delete the server. If the server is in use, an error message displays.
DHCP server settings
The following table describes the DHCP server settings.
Table 1 DHCP server settings
Server Information Field
Select a host server from the drop-down list of available host servers.
Primary DNS IPv4 Address
This field specifies primary DNS IPv4 address.
Secondary DNS IPv4 Address
This field specifies secondary DNS IPv4 address.
Primary TFTP Server IPv4 Address (Option 150)
You can enable the IP phones to access the TFTP server using DHCP custom option 150. This is the method that Cisco recommends.
This field specifies the IPv4 address for primary Trivial File Transfer Protocol (TFTP) server.
Secondary TFTP Server IPv4 Address (Option 150)
This field specifies the IPv4 address for secondary TFTP server.
Bootstrap Server IPv4 Address
This field specifies the address of the server that is used in the next step of the bootstrap process. You can use as the IPv4 address of the TFTP server or as the default value to DHCP server address if the server supplies the next bootstrap service.
The Domain Name specifies the domain name that you should use when resolving hostname via the Domain Name System.
TFTP Server Name (Option 66)
You can enable the IP phones to access the TFTP server by using DHCP option 66.
Use this field to identify a TFTP server. You can configure only one DNS name or a dotted decimal IP address in this parameter.
ARP Cache Timeout
This field specifies the timeout in seconds for ARP cache entries. Specify the time as a 32-bit unsigned integer. The default for the Cisco Network Registrar (CNR) DHCP server specifies 60 seconds.
IP Address Lease Time
The DHCP server uses the information in this field to specify the lease time that it is willing to offer. Specify the time in units of seconds and as a 32-bit unsigned integer. The default for the CNR DHCP server specifies seven days (604,800 seconds).
Renewal(T1) Time (sec)
This field specifies the time interval from address assignment until the client transitions to the RENEWING state. Typically, set this field to half the value of the IP address lease time. For example, if the IP address lease time is typically set to 60,000 seconds, the renewal time gets set to 30,000 seconds.
Rebinding (T2) Time (sec)
This field specifies the time interval from address assignment until the client transitions to the REBINDING state. Specify the value in units of seconds and as a 32-bit unsigned integer. Typically, set this field to approximately 75 percent of the value of the IP address lease time. For example, if the IP address lease time is set to 60,000 seconds, the rebinding time typically gets set to about 45,000 seconds. In Windows, 85 percent of the value of the IP address lease time represents the standard.