CHAPTER 1 Understanding Ethernet Networking 23
network segment, a collection of network devices connected to a single switch.
(If this network segment comprises your entire network, you can call it a
switched network.)
1
Switch
Computer Computer
Computer
FIGURE 1.9
You can use a switch as the central connection point for your network.
The switch then forwards data from one network node to another. On basic
switches such as the type used in homes or small offices, the switch usually
reads the MAC address of the destination node in each ethernet frame and
sends the frame directly to that device. Most switches maintain a switching
table, a record of the MAC addresses and network port numbers used by each
device on the network. As you use your network, the switch makes note of
each new MAC address and adds it to the switching table, which improves
overall switch performance.
You can also use a switch to send data across multiple network segments. For
example, you might have a network segment in one room or office and a sec-
ond segment in the room or office next door. Similarly, if your network out-
grows your original switch, you might add a second switch to the network
instead of upgrading to a switch with more ports. To join the two segments,
you have three choices:
■ Many older switches come with a special uplink port that’s designed to
connect two switches by running a
network cable from the uplink port
of one switch to the uplink port of note The network config-
uration shown in Fig-
the other switch. On some of these ure 1.9—that is, multiple network
nodes joined to a central connec-
switches, a button controls whether
tion point—is called the star
the port is used as a regular RJ-45 topology.
port or an uplink port.
24 Networking with Microsoft® Windows Vista™
■ Use an ethernet crossover cable to link two switches by running the
cable from any port in the first switch to any port in the second switch.
1 ■ Get switches where the ports support Auto Crossover (also called Auto
MDI/MDI-X crossover detection; MDI stands for Medium-Dependent
Interface). This enables you to connect two switches without using an
uplink port or a crossover cable.
As with NICs and cables, all switches support one or more of the ethernet
standards. For example, a Fast Ethernet switch will almost always support
10/100 connections, whereas a Gigabit Ethernet switch will usually support
10/100/1000 connections. Make sure you match your switch to the ethernet
standard you’re using on your network.
Understanding Routers
You saw in the previous section that a switch forwards ethernet packets
according to the device MAC address in the frame header. This works
extremely well, and most modern switches are high-performance devices.
However, the inherent limitation of a switch becomes obvious when you want
to add an Internet connection to your network:
■ When you want to request data from a web server, it’s impossible to
know the MAC address of the remote server computer, so the switch
has no way to forward the data request.
■ When a web server wants to send data to your computer, it’s impossi-
ble for the remote machine to know your computer’s MAC address, so
the switch cannot get the data to your computer.
In other words, the MAC address-based forwarding performed by a switch is
limited to LAN traffic and cannot be used to handle WAN (wide area network)
data.
To solve this problem, you need to add a router to your network (see Figure
1.10). A router is a device that makes decisions about where to send the net-
work packets it receives. So far, this sounds
suspiciously similar to a switch. The major
difference is that while a switch uses a note A wide area network
is network that cov-
MAC address-based switching table to for- ers a wide geographical area.
Some corporations use wide area
ward data, a router uses a routing table
networks, but the Internet is the
that tracks IP addresses, unique addresses wide area network.
assigned to every Internet host and to
CHAPTER 1 Understanding Ethernet Networking 25
every computer on your network. For example, this is useful when the com-
puters share a high-speed Internet connection, because the router ensures that
the Internet data goes to the computer that requested it. To make this work,
1
you plug your high-speed modem directly into the special WAN port in the
back of the router.
FIGURE 1.10
You add a router to your network when you want to add Internet access.
Understanding IP Addresses
An IP address is a 32-bit value assigned to a computer by a network adminis-
trator or, if you’ve signed up for an Internet account, by your Internet service
provider (ISP). As you’ll see in a minute, these addresses are designed so that
every host and router on the Internet or within a network has a unique
address. That way, when an application needs to send data to a particular
locale, it knows that the destination address it plops into the packet header
will make sure that everything ends up where it’s supposed to.
The problem with IP addresses is their “32-bitness.” Here’s an example:
1100110111010000111000100000010
26 Networking with Microsoft® Windows Vista™
Not very inviting, is it? To make these
numbers easier to work with, you use
dotted-decimal notation (also known in the
tip You can convert a value
from binary to decimal
1 using Windows Vista’s Calculator.
trade as dotted-quad notation). This notation Select Start, All Programs, Acces-
divides the 32 bits of an IP address into sories, Calculator, and then, in the
four groups of 8 bits each (each of these Calculator window, select View,
groups is called a quad), converts each Scientific. Click the Bin (binary)
option, use the text box to type
group into its decimal equivalent, and then
the 1s and 0s of the binary value
separates these numbers with dots. you want to convert, and click the
Let’s look at an example. Here’s the previ- Dec (decimal) option.
ous IP address grouped into four 8-bit
quads:
11001101 11010000 01110001 00000010
Now you convert each quad into its decimal equivalent. When you do, you
end up with this:
11001101 11010000 01110001 00000010
205 208 113 2
Now you insert dots between each decimal number to get the dotted-decimal
form of the address:
205.208.113.2
The Router and Dynamic IP Addressing
The MAC addresses of network devices are assigned in advance by the device
manufacturer. How, then, are IP addresses assigned? For the servers and other
remote machines you deal with on the Internet, each network that wants on
the Internet must sign up with a domain registrar (such as VeriSign.com or
Register.com). In turn, the registrar assigns that network a block of IP
addresses that the administrator can then dole out to each computer (or, in
the case of an ISP, to each customer).
For your own network, however, the IP addresses are assigned as follows:
■ Your router is given its own IP address—called the public IP address—
from the pool of addresses controlled by your ISP. Internet data sent to
any computer on your network is first sent to the router’s external IP
address.
■ The computers on your network are assigned IP addresses. In other
words, when a computer logs on to the network, it is assigned an IP
CHAPTER 1 Understanding Ethernet Networking 27
address from a pool of available
addresses. When the computer logs
off, the address it was using is
note When a device such
as a router is set up
1
as the sole connection point
returned to the pool. The system
between a network and the
that manages this dynamic alloca- Internet, that device is called a
tion of addresses is called the gateway.
Dynamic Host Configuration Protocol
(DHCP), and the computers or devices that implement DHCP are called
DHCP servers. In most home networks, the router acts as a DHCP server.
In most cases, the range of addresses is from 192.168.1.1 to 192.168.1.254.
(On some routers, the range is from 192.168.0.1 to 192.168.0.254.) The router
itself usually takes the 192.168.1.1 address (this is called its private IP address),
and the pool of possible addresses is usually some subset of the total range,
such as between 192.168.1.100 and 192.168.1.150.
The big advantage of this setup is that your network is never exposed to the
Internet. All communication goes through the router’s public IP address; so as
far as, say, a web or email server is concerned, it’s communicating with a
device at that address. The router is able to get the correct data to your com-
puter because when you initially request data, it adds your computer’s private
IP address and the number of the communications port your computer is
using and stores this data in a routing table. When data comes back from the
Internet, the router converts the public destination IP address of the data to
the private address of your computer, a process known as network address
translation (NAT).
The Router as Firewall
On a small network, the main function of a router is to be used as a gateway
between your network and the Internet. Through the magic of NAT, your net-
work cannot be seen from any device attached to the Internet; as far as the
Internet is concerned, your network is nothing but a router. (For this reason,
an Internet-connected router that performs NAT duties is sometimes called an
edge router.) NAT, therefore, acts as a kind of simple firewall, a technology that
prevents unwanted data from reaching a network.
However, most modern routers go one step further and come with separate
firewall software. This gives you an interface for controlling and managing
the firewall, which mostly means opening and closing specific software ports
used by applications. For example, you’ll see in Chapter 19, “Setting Up a
Website,” that to successfully use a web server on your network you need to
configure the router’s firewall to allow incoming connections on port 80.
28 Networking with Microsoft® Windows Vista™
The Router as Switch
You’ve seen that a router can act as a gateway device and a firewall device,
1 but there’s a third hat that’s worn by most modern routers: a switch device. A
typical router has a few RJ-45 ports (usually four; see Figure 1.11); so, as with
a dedicated switch, you can create ethernet connections for computers and
other devices by running ethernet cable from each device to a router port.
WAN port (for broadband modem) RJ-45 ports
FIGURE 1.11
Most routers have built-in switches, meaning you can use the router’s ports to connect devices
to your network.
This means that if you have a small ethernet network, you might be able to
get away with using just a router as your network’s connection point. Figure
1.12 shows this network configuration.
On the other hand, if your network is larger or if you have a number of other
devices you need to connect, your router might not have enough ports.
Similarly, you may be upgrading your network to Gigabit Ethernet and your
router only comes with Fast Ethernet (or 10/100) ports. In both cases, the easiest
solution is to leave your existing router in place and add to the network a dedi-
cated switch that meets your needs. In this scenario, you connect the broad-
band modem to the router’s WAN port, you run a network cable from one of
the router’s RJ-45 ports to an RJ-45 port on the switch, and you connect your
network devices to the switch. Figure 1.13 shows this network configuration.
CHAPTER 1 Understanding Ethernet Networking 29
Internet
1
Cable/DSL Modem
Router
Computer Computer
Computer
FIGURE 1.12
A small ethernet network can use a single router as both the gateway and the switch.
Internet
Cable/DSL Modem
Router
Switch
Computer Computer
Computer
FIGURE 1.13
Larger ethernet networks may require a dedicated switch as the central network connection point.
30 Networking with Microsoft® Windows Vista™
Understanding Other Ethernet Devices
To round out your look at ethernet hardware, the next few sections give you a
1 quick overview of a few other devices you can connect to your ethernet net-
work.
Network Attached Storage
A network attached storage (NAS) device contains one or more hard drives and
plugs into a switch or router. This enables the client computers on the network
to store files on the device rather than on a network share. If you have one or
two internal hard drives lying around, you can purchase just the NAS enclo-
sure and attach the drives yourself. In this case, make sure that the NAS
enclosure’s interface supports your hard drive type (for example, ATA versus
SATA).
Many NAS devices also come with one or more USB ports, which means you
can expand the device’s storage space by attaching one or more external USB
hard drives. Figure 1.14 shows a typical NAS enclosure.
FIGURE 1.14
With a NAS enclosure, you attach one or more internal and external hard drives that a
network computer can then access directly.
CHAPTER 1 Understanding Ethernet Networking 31
Print Server
To print over the network, you normally share a printer that’s attached to one
of the network computers. However, this requires that the computer with the 1
printer share that printer, it requires each person who wants to use the printer
to connect to it, and it requires that the network computer always be on.
These aren’t onerous demands, but they sometimes create enough of a hassle
to make network administrators turn to dedicated print servers, devices that
connect printers directly to the network.
In some cases, a printer comes with a built-in RJ-45 port, so you need only run
ethernet cable from the printer to an RJ-45 port in the switch or router.
However, most consumer-grade printers don’t have a built-in NIC. In that
case, you can get a print server that’s a separate box with either a parallel
port or a USB port (or both), as well as an RJ-45 port (see Figure 1.15). You
connect the printer to the print server’s parallel or USB port, and then connect
the print server’s RJ-45 port to the switch or router.
FIGURE 1.15
A print server device enables you to connect a printer directly to the network without having
to share it through a network computer.
32 Networking with Microsoft® Windows Vista™
Digital Media Receiver
Windows Vista programs such as Windows Media Player and Windows Media
1 Center can broadcast digital media over an ethernet connection. This is called
streaming the media, and the data itself is called a stream. Other Windows
Vista computers on your network can pick up and play that stream. However,
you can also use a device called a digital media receiver (DMR) to access a
media stream being sent over an ethernet connection and then play that
stream through connected equipment such as speakers, audio receivers, or a
TV. Examples of DMRs include the Xbox 360, the Roku SoundBridge, and the
D-Link MediaLounge. Other DMR types include certain digital media players
(such as MP3 players) and digital picture frames, which display images
streamed over a network connection.
Powerline Adapter
You use a powerline adapter to connect a computer to your network using the
AC power lines in your home or office. This device isn’t a NIC per se. Instead,
it acts as a kind of bridge that connects a regular ethernet NIC to your net-
work without having to connect that NIC directly to a switch or router. You
actually need at least two powerline adapters. One adapter plugs into an AC
outlet near your switch or router, and you then run ethernet cable from the
switch/router to the powerline adapter, which effectively connects your home
or office power lines to the network. You then plug a second powerline adapter
into an AC outlet near the device you want to network, and you run an ether-
net cable from the device’s NIC to the powerline adapter. You can repeat this
for any number of devices.
A Buyer’s Guide to Ethernet Hardware
If you’re looking to purchase new ethernet hardware, whether you’re starting
from scratch or looking to upgrade your existing equipment, the buying
process is not always easy because you often face a thicket of jargon terms
and a list of product specifications that seems to require an advanced degree
in electrical engineering to figure out. To make it easier to choose the right
ethernet hardware, the next few sections give you a few pointers on what to
look for and what to avoid when purchasing the four main hardware types:
NICs, cables, switches, and routers.
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