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Chapter 2: Networking
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initialization configures the cable modem with a CM IP (Cable Modem Internet Protocol) address,
as shown in Figure 3, so the cable company can communicate directly with the CM itself.
Networking Section
The Networking section of your gateway also uses TCP/IP (Transmission Control Protocol/
Internet Protocol) for the PCs you connected on the LAN side. TCP/IP is a networking protocol
that provides communication across interconnected networks, between computers with diverse
hardware architectures and various operating systems.
TCP/IP requires that each communicating device be configured with one or more TCP/IP stacks,
as illustrated by Figure 4. On a PC, you often use software that came with the PC or its network
interface (if you purchased a network interface card separately) to perform this configuration. To
communicate with the Internet, the stack must also be assigned an IP (Internet Protocol) address.
192.168.100.1 is an example of an IP address. A TCP/IP stack can be configured to get this IP
address by various means, including a DHCP server, by you directly entering it, or sometimes by
a PC generating one of its own.
Ethernet requires that each TCP/IP stack on the Wireless Cable Gateway also have associated with
it an Ethernet MAC (Media Access Control) address. MAC addresses are permanently fixed into
network devices at the time of their manufacture. 00:90:64:12:B1:91 is an example of a MAC
address.
Data packets enter and exit a device through one of its network interfaces. The gateway offers
Ethernet, USB, and 802.11b/g wireless network interfaces on the LAN side and the EURO-DOCSIS
network interface on the WAN side.
When a packet enters a network interface, it is offered to all the TCP/IP stacks associated with the
device side from which it entered. But only one stack can accept it — a stack whose configured
Ethernet address matches the Ethernet destination address inside the packet. Furthermore, at a
packet’s final destination, its destination IP address must also match the IP address of the stack.
Each packet that enters a device contains source MAC and IP addresses telling where it came
from, and destination MAC and IP addresses telling where it is going to. In addition, the packet
contains all or part of a message destined for some application that is running on the destination