Using Cisco Ip Phones With A Dhcp Server - Cisco PIX 500 Series Configuration Manual

Configuring a DHCP Server
Table 10-1
Table 10-1
Option Code
0
1
12
50
51
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 10-4
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 security
appliance DHCP server provides values for both options in the response if they are configured on the
security appliance.
You can configure the security appliance to send information for most options listed in RFC 2132. The
following example shows the syntax for any option number, as well as the syntax for commonly-used
options 66, 150, and 3:
Cisco Security Appliance Command Line Configuration Guide
10-4
shows the DHCP options that are not supported by the dhcpd option command.
Unsupported DHCP Options
Description
DHCPOPT_PAD
HCPOPT_SUBNET_MASK
DHCPOPT_HOST_NAME
DHCPOPT_REQUESTED_ADDRESS
DHCPOPT_LEASE_TIME
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.
Chapter 10 Configuring DHCP, DDNS, and WCCP Services
topic for more information about
"Using
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