For computers to send and receive information to each other, they must have
some form of addressing so that each end device on the network knows what
information to read and what information to ignore. This capability is important
both for the computers that ultimately use the information and for the
devices that deliver information to end stations, such as switches and routers.
Every computer on a network has two addresses:
• MAC address: A manufacturer-allocated ID number (such as a global serial
number) that is permanent and unique to every network device on Earth.
MAC addresses are analogous to a social security number or other national
identification number. You have only one, it stays the same wherever you go,
and no two people (devices) have the same number. MAC address are formatted
using six pairs of hexadecimal numbers, such as 01-23-45-67-89-AB.
Hexadecimal or “hex” is a base 16 numbering scheme that uses the numbers
0 through 9 and the letters A through F to count from 0 to 15. This
might seem odd, but it provides an easy translation from binary (which uses
only 1s and 0s), which is the language of all computers.
• IP address: This address is what matters most to basic networking. Unlike a
MAC address, the IP address of any device is temporary and can be
changed. It is often assigned by the network itself and is analogous to your
street address. It only needs to be unique within a network. Someone else’s
network might use the same IP address, much like another town might have
the same street (for example, 101 Main Street). Every device on an IP network
is given an IP address, which looks like this: 192.168.1.100.
The format of this address is called dotted-decimal notation. The period separators
are pronounced “dot,” as in one ninety two dot one sixty eight dot....”
Because of some rules with binary, the largest number in each section is 255.
In addition to breaking up the number, the dots that appear in IP addresses
allow us to break the address into parts that represent networks and hosts. In
this case, the “network” portion refers to a company, university, government
agency, or your private network. The hosts would be the addresses of all the
computers on the individual network. If you think of the network portion of
the address as a street, the hosts would be all the houses on that street. If you
could see the IP addresses of everyone who is on the same network segment as
you, you would notice that the network portion of the address is the same for
all computers, and the host portion changes from computer to computer. An
example will probably help. Think of an IP address as being like your home
address for the post office: state.city.street.house-number.
Each number in the IP address provides a more and more specific location so
that the Internet can find your computer among millions of other computers.
The Internet is not organized geographically like the postal system, though.
The components of the address (intentionally oversimplified) are majornetwork.
minor-network.local-network.device.