Configuring the DHCP Server Feature

The dhcpd wins Command

The dhcpd wins command specifies the IP address of one or two WINS servers for DHCP clients. The no dhcpd wins command removes the WINS IP address(es) from the configuration. The syntax is

pix(config)#dhcpd wins wins1 [wins2]
pix(config)#no dhcpd wins

The first of the following examples defines one WINS server. The second example defines two WINS servers:

pix(config)#dhcpd wins 192.168.100.5
pix(config)#dhcpd wins 192.168.100.5 192.168.101.5 

The dhcpd ping_timeout Command

The dhcpd ping_timeout command allows a short delay to be configured, in milliseconds, before responding to a DHCP client request. This delay allows the PIX Firewall to work as a backup DHCL server. The no dhcpd ping_timeout command removes the delay. The syntax is

pix(config)#dhcpd ping_timeout timeout
pix(config)#no dhcpd ping_timeout

This example sets the DHCP ping_timeout to 750 milliseconds.

pix(config)#dhcpd ping_timeout 750

Using Cisco IP Phones with a DHCP Server

A growing number of organizations with small branch offices are implementing a Cisco IP Telephony VoIP (Voice over IP) solution. A common implementation is to install the Cisco CallManager at the central office and use it to control IP Phones at the small branch offices. The benefits to this implementation include the following:

• Centralizes call processing

• Reduces the equipment required

• Eliminates the administration of additional Cisco CallManager servers

• Eliminates other servers at branch offices

Part of the simplicity of the Cisco IP Telephony solution is that the phones can download their configuration from a TFTP server. To eliminate the need to preconfigure the Cisco IP Phone with the phone IP address and the IP address of the TFTP server, the phone sends out a DHCP request with the option parameter set to 150 or 66 to a DHCP server.

PIX Firewall version 6.2 introduced the two new options for the dhcpd command specifically to support VoIP installations. Use the no form of the command to remove the configuration entry. The syntax is

pix(config)#dhcpd option 66 ascii {server_name | server_ip_str}
pix(config)#no dhcpd option 66
pix(config)#dhcpd option 150 ip server_ip1 [server_ip2]
pix(config)#no dhcpd option 150

Cisco IP Phones can include both option 150 and 66 requests in a single DHCP request. In this case, the PIX Firewall DHCP server assigns values for both options in the response if they’re configured on the PIX Firewall.

This partial configuration demonstrates configuring the firewall with DHCP support for the dhcpd option 66 and option 150 features. Note, the server IP addresses are on the same network as the inside interface and outside the range of available IP addresses assigned to the DHCP server.

pix(config)#ip address inside 192.168.1.1 255.255.255.0
pix(config)#dhcpd address 192.168.1.6-192.168.1.254
pix(config)#dhcpd dns 192.168.100.5 192.168.101.5
pix(config)#dhcpd wins 192.168.100.5
pix(config)#dhcpd domain test.com
pix(config)#dhcpd option 66 ascii 192.168.1.5
pix(config)#dhcpd option 150 192.168.1.4 192.168.1.5
pix(config)#dhcpd enable

Verifying and Monitoring DHCP Configuration

In addition to performing a write terminal command to see the configuration, the PIX Firewall offers the following commands:

This partial configuration demonstrates configuring the DHCP features for a SOHO implementation.

pix(config)#ip address inside 192.168.1.1 255.255.255.0
pix(config)#dhcpd address 192.168.1.2-192.168.1.254
pix(config)#dhcpd dns 192.168.100.5 192.168.101.5
pix(config)#dhcpd wins 192.168.100.5
pix(config)#dhcpd lease 7200
pix(config)#dhcpd ping_timeout 750
pix(config)#dhcpd domain test.com
pix(config)#dhcpd enable

This next example is sample output from the show dhcpd command:

pix(config)#show dhcpd
dhcpd address 192.168.1.2-192.168.1.254 inside
dhcpd domain test.com
dhcpd lease 7200
dhcpd ping_timeout 750
dhcpd dhcpd dns 192.168.100.5 192.168.101.5
dhcpd wins 192.168.100.5
dhcpd enable inside 

This next example is sample output from the show dhcpd binding command:

The following is sample output from the show dhcpd statistics command:

pix(config)#show dhcpd statistics
Address Pools 1
Automatic Bindings 1
Expired Bindings 1
Malformed messages 0
 
Message Received
BOOTREQUEST 0
DHCPDISCOVER 1
DHCPREQUEST 2
DHCPDECLINE 0
DHCPRELEASE 0
DHCPINFORM 0
 
Message Sent
BOOTREPLY 0
DHCPOFFER 1
DHCPACK 1
DHCPNAK 1