Using Cisco Ip Phones With A Dhcp Server - Cisco 7604 Configuration Manual

Configuring DHCP
Table 8-1
Option Code
52
53
54
58
59
61
67
82
255
Specific options, DHCP option 3, 66, and 150, are used to configure Cisco IP Phones. See the
Cisco IP Phones with a DHCP Server" section on page 8-38
configuring those options.

Using Cisco IP Phones with a DHCP Server

Enterprises with small branch offices that implement a Cisco IP Telephony Voice over IP solution
typically implement Cisco CallManager at a central office to control Cisco IP Phones at small branch
offices. This implementation allows centralized call processing, reduces the equipment required, and
eliminates the administration of additional Cisco CallManager and other servers at branch offices.
Cisco IP Phones download their configuration from a TFTP server. When a Cisco IP Phone starts, if it
does not have both the IP address and TFTP server IP address preconfigured, it sends a request with
option 150 or 66 to the DHCP server to obtain this information.
•
•
Cisco IP Phones might also include DHCP option 3 in their requests, which sets the default route.
Cisco IP Phones might include both option 150 and 66 in a single request. In this case, the FWSM DHCP
server provides values for both options in the response if they are configured on the FWSM.
You can configure the FWSM to send information for most options listed in RFC 2132. The following
table shows the syntax for any option number, as well as the syntax for commonly-used options 66,150,
and 3:
•
•
•
Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide using ASDM
8-38
Unsupported DHCP Options
Description
DHCPOPT_OPTION_OVERLOAD
DHCPOPT_MESSAGE_TYPE
DHCPOPT_SERVER_IDENTIFIER
DHCPOPT_RENEWAL_TIME
DHCPOPT_REBINDING_TIME
DHCPOPT_CLIENT_IDENTIFIER
DHCPOPT_BOOT_FILE_NAME
DHCPOPT_RELAY_INFORMATION
DHCPOPT_END
DHCP option 150 provides the IP addresses of a list of TFTP servers.
DHCP option 66 gives the IP address or the hostname of a single TFTP server.
To provide information for DHCP requests that include an option number as specified in RFC 2132,
enter the following command:
hostname(config)# dhcpd option number value
To provide the IP address or name of a TFTP server for option 66, enter the following command:
hostname(config)# dhcpd option 66 ascii server_name
To provide the IP address or names of one or two TFTP servers for option 150, enter the following
command:
hostname(config)# dhcpd option 150 ip server_ip1 [server_ip2]
Chapter 8 Configuring IP Routing and DHCP Services
topic for more information about
"Using
OL-20748-01