Lucent Technologies PortMaster - Manual (Page 43)

Configuring Global Settings 3-5
Setting the Default Route Gateway
1. Using the telephone interface, the cable modem dials the PortMaster and establishes
a PPP connection. The PortMaster assigns IP address 192.168.33.10 to the telephone
interface of the cable modem.
2. Using the telephone interface, the cable modem broadcasts a DHCP request. The
destination of the request is 255.255.255.255 and the source is 192.168.33.10.
3. The PortMaster forwards the request to the DHCP server by substituting the IP
address of the DHCP server (10.66.98.96) for the broadcast destination address.
4. The DHCP server responds with configuration information for the cable modem and
an IP address (172.16.98.67) for the coaxial cable interface on the cable modem.
5. Using the configuration information received from the DHCP server, the cable
modem dynamically assigns 172.16.98.67 to the cable interface, and configures the
cable modem so that upstream IP packets leave the cable modem via the telephone
interface with the IP address of the cable interface (172.16.98.67) as the source
address. Because packets now carry the source address of the cable interface,
response to these packets travels via the coaxial cable.
The ComOS does not add routes to its table when forwarding or returning DHCP
requests. It transparently forwards and returns DHCP requests from dial-in clients to the
specified server.
To view DHCP relaying information, use the set console command followed by the set
debug 0x81 command. See the PortMaster Troubleshooting Guide for debugging
information.
To disable DHCP reply information, enter the following command:
Command> set dhcp server 0.0.0.0.
The PortMaster does not forward packets to the address 255.255.255.255.
Setting the Default Route Gateway
The default route gateway is the address of a router of last resort to which packets are
sent when the PortMaster has no routing information for a packet. The default route
gateway is also the destination address the PortMaster selects when it cannot locate the
destination of a packet on the local Ethernet segment. You identify the default gateway
by its IP address entered in dotted decimal notation. A PortMaster can never be its own
default gateway.