68 Chapter 4 Determining DHCP server configuration and IP address
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If an external DHCP server is present
If an external DHCP is present, then the BCM50 system uses the IP configuration supplied by the
external DHCP server.
In this case, the DHCP server on the main unit only supplies IP Phones with IP configuration
information. It does not supply any other devices with IP settings. This means that the
administrator does not need to set up the external DHCP server 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 the
IP Phones. It uses the top 20 percent of a subnet.
For example:
If the external DHCP server supplies the following IP address to the BCM50: 177.218.21.45
(subnet mask is 255.255.255.0); then the BCM50 DHCP server reserves the following range:
177.218.21.200 – 177.218.21.254.
This default range can be verified and changed using Element Manager.
The administrator must ensure that this range agrees with the network configuration — the range is
not used by the external DHCP server.
BCM50a or BCM50e (with integrated router)
By default, the BCM50a main unit or BCM50e main unit is configured with a dynamic IP address,
meaning that it requests an IP configuration from a DHCP server. Since the integrated router has a
DHCP server, this DHCP server responds to the request.
By default, the router LAN IP address is 192.168.1.1, and the IP address assigned to the BCM50
system is the first IP address in the DHCP pool. If the DHCP pool started at 192.168.1.190, then
the BCM50 is 192.168.1.190 even though the router is 192.168.1.1. So the BCM50 system
receives the IP address 192.168.1.2 (subnet mask is 255.255.255.0) from the DHCP server on the
integrated router.
The DHCP server on the integrated router supplies the information (primary and secondary TPS
server information, VLAN ids) to the IP Phones enabling them to connect to the BCM50. If the IP
address of the integrated router is changed, then the IP address reserved for the BCM50 is
automatically changed. The DHCP server on the integrated router automatically updates the S1
and S2 IP address.
Warning: The DHCP server on the main unit is enabled by default. If your
network already contains a DHCP server, then disable the DHCP server on the
main unit. Refer to “To disable the DHCP server on the main unit” on page 69 for
more information on disabling the DHCP server.
