19216811.liveChapter 3: Networking
Illustrations contained in this document are for representation only.
72
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 device. IRC used in an Internet instant messaging program, HTTP used by a web
browser, and FTP used by a file transfer program are all examples of applications. Inside the