70 Chapter 4 Determining DHCP server configuration and IP addressNN40020-302If an external DHCP server is presentIf an external DHCP is present, then the BCM50 system uses the IP configuration supplied by theexternal DHCP server. In this case, the DHCP server on the main unit supplies only IP Phoneswith IP configuration information. The DHCP server on the main unit does not supply any otherdevices with IP settings. This means that the administrator need not set up the external DHCPserver to supply configuration settings to the IP Phones.The DHCP server on the main unit must configure a range of IP addresses to supply to theIP Phones. The DHCP server uses the top 20 percent of a subnet.For example, if the external DHCP server supplies the IP address 177.218.21.45 (subnet mask is255.255.255.0) to the BCM50, then the BCM50 DHCP server reserves the range 177.218.21.200to 177.218.21.254.You can verify and change this default range using Element Manager.The administrator must ensure that this range agrees with the network configuration—the externalDHCP server does not use the range.BCM50a, BCM50ba, BCM50e, and BCM50be main units(with integrated router)You can select the DHCP server option to use with the BCM50 integrated router main units. Youcan select to use the integrated router or you can disable the integrated router and use the DHCPserver that is on the main unit. Select the DHCP server option through Element Manager(Configuration > Data Services > DHCP Server > General Settings tab).If you select the standard DHCP server on the main unit, you must first disable the DHCP serveron the integrated router. You can then configure the DHCP server functionality in the same way asa non-router version.If you select the DHCP server on the integrated router you can configure the router using the routerWebGUI tool.By default, the integrated router is selected and you configure the BCM50a, BCM50ba, BCM50e,and BCM50be main units with a dynamic IP address, meaning that these units request an IPconfiguration from a DHCP server. Because the integrated router has a DHCP server, this DHCPserver responds to the request.Warning: The DHCP server on the main unit is enabled (IP Phones only) bydefault. If your network already contains a DHCP server, then disable the DHCPserver on the main unit. For more information about disabling the DHCP server onthe main unit, see the procedure To configure DHCP server settings on page 142.
