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Broadband Terminology
This section provides
a basic introduction to the technologies that underlie the Internet. It
was written with the novice end-user in mind and is not intended to be
a comprehensive survey of all Internet-based technologies. Subsections
provide a short overview of each topic.
This section is a
basic primer on the relevant technologies.
For those who desire a deeper understanding of the concepts covered here,
we offer suggested reading.
What does
broadband mean?
"Broadband" is the general term used to refer to high-speed
network connections. In this context, Internet connections via cable modem
and Digital Subscriber Line (DSL) are frequently referred to as broadband
Internet connections. "Bandwidth" is the term used to describe
the relative speed of a network connection -- for example, most current
dial-up modems can support a bandwidth of 56 kbps (thousand bits per second).
There is no set bandwidth threshold required for a connection to be referred
to as "broadband", but it is typical for connections in excess
of 1 Megabit per second (Mbps) to be so named.
What is cable modem
access?
A cable modem allows a single computer (or network of computers) to connect
to the Internet via the cable TV network. The cable modem usually has
an Ethernet LAN (Local Area Network) connection to the computer, and is
capable of speeds in excess of 5 Mbps.
Typical speeds tend
to be lower than the maximum, however, since cable providers turn entire
neighborhoods into LANs which share the same bandwidth. Because of this
"shared-medium" topology, cable modem users may experience somewhat
slower network access during periods of peak demand, and may be more susceptible
to risks such as packet sniffing and unprotected windows shares than users
with other types of connectivity.
What is DSL access?
Digital Subscriber Line (DSL) Internet connectivity, unlike cable modem-based
service, provides the user with dedicated bandwidth. However, the maximum
bandwidth available to DSL users is usually lower than the maximum cable
modem rate because of differences in their respective network technologies.
Also, the "dedicated bandwidth" is only dedicated between your
home and the DSL provider's central office -- the providers offer little
or no guarantee of bandwidth all the way across the Internet.
DSL access is not
as susceptible to packet sniffing as cable modem access, but many of the
other security risks we'll cover apply to both DSL and cable modem access.
How are broadband
services different from traditional dial-up services?
Traditional dial-up Internet services are sometimes referred to as "dial-on-demand"
services. That is, your computer only connects to the Internet when it
has something to send, such as email or a request to load a web page.
Once there is no more data to be sent, or after a certain amount of idle
time, the computer disconnects the call. Also, in most cases each call
connects to a pool of modems at the ISP, and since the modem IP addresses
are dynamically assigned, your computer is usually assigned a different
IP address on each call. As a result, it is more difficult (not impossible,
just difficult) for an attacker to take advantage of vulnerable network
services to take control of your computer.
Broadband services are referred to as "always-on" services because
there is no call setup when your computer has something to send. The computer
is always on the network, ready to send or receive data through its network
interface card (NIC). Since the connection is always up, your computer's
IP address will change less frequently (if at all), thus making it more
of a fixed target for attack.
What's more, many
broadband service providers use well-known IP addresses for home users.
So while an attacker may not be able to single out your specific computer
as belonging to you, they may at least be able to know that your service
providers' broadband customers are within a certain address range, thereby
making your computer a more likely target than it might have been otherwise.
How is broadband
access different from the network I use at work?
Corporate and government networks are typically protected by many layers
of security, ranging from network firewalls to encryption. In addition,
they usually have support staff who maintain the security and availability
of these network connections.
Although your ISP
is responsible for maintaining the services they provide to you, you probably
won't have dedicated staff on hand to manage and operate your home network.
You are ultimately responsible for your own computers. As a result, it
is up to you to take reasonable precautions to secure your computers from
accidental or intentional misuse.
What is a protocol?
A protocol is a well-defined specification that allows computers to communicate
across a network. In a way, protocols define the "grammar" that
computers can use to "talk" to each other.
What is IP?
IP stands for "Internet Protocol". It can be thought of as the
common language of computers on the Internet. There are a number of detailed
descriptions of IP given elsewhere, so we won't cover it in detail in
this document. However, it is important to know a few things about IP
in order to understand how to secure your computer. Here we'll cover IP
addresses, static vs. dynamic addressing, NAT, and TCP and UDP Ports.
What is an
IP address?
IP addresses are analogous to telephone numbers - when you want to call
someone on the telephone, you must first know their telephone number.
Similarly, when a computer on the Internet needs to send data to another
computer, it must first know its IP address. IP addresses are typically
shown as four numbers separated by decimal points, or "dots".
For example, 10.24.254.3 and 192.168.62.231 are IP addresses.
If you need to make
a telephone call but you only know the person's name, you can look them
up in the telephone directory (or call directory services) to get their
telephone number. On the Internet, that directory is called the Domain
Name System, or DNS for short. If you know the name of a server, say www.cert.org,
and you type this into your web browser, your computer will then go ask
its DNS server what the numeric IP address is that is associated with
that name.
Every computer on the Internet has an IP address associated with it that
uniquely identifies it.
However, that address
may change over time, especially if the computer is: dialing into an Internet
Service Provider (ISP), connected behind a network firewall, connected
to a broadband service using dynamic IP addressing.
What are static
and dynamic addressing?
Static IP addressing occurs when an ISP permanently assigns one or more
IP addresses for each user. These addresses do not change over time. However,
if a static address is assigned but not in use, it is effectively wasted.
Since ISPs have a limited number of addresses allocated to them, they
sometimes need to make more efficient use of their addresses.
Dynamic IP addressing
allows the ISP to efficiently utilize their address space. Using dynamic
IP addressing, the IP addresses of individual user computers may change
over time. If a dynamic address is not in use, it can be automatically
reassigned to another computer as needed.
What is NAT?
Network Address Translation (NAT) provides a way to hide the IP addresses
of a private network from the Internet while still allowing computers
on that network to access the Internet. NAT can be used in many different
ways, but one method frequently used by home users is called "masquerading".
Using NAT masquerading,
one or more devices on a LAN can be made to appear as a single IP address
to the outside Internet. This allows for multiple computers in a home
network to use a single cable modem or DSL connection without requiring
the ISP to provide more than one IP address to the user. Using this method,
the ISP-assigned IP address can be either static or dynamic. Most network
firewalls support NAT masquerading.
What are TCP and
UDP Ports?
TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are
both protocols that use IP. Whereas IP allows two computers to talk to
each other across the Internet, TCP and UDP allow individual applications
(also known as "services") on those computers to talk to each
other.
In the same way that a telephone number or physical mail box might be
associated with more than one person, a computer might have multiple applications
(e.g. email, file services, web services) running on the same IP address.
Ports allow a computer to differentiate services such as email data from
web data. A port is simply a number associated with each application that
uniquely identifies that service on that computer. Both TCP and UDP use
ports to identify services. Some common port numbers are 80 for web (HTTP),
25 for email (SMTP), and 53 for Dmain Name System (DNS).
What is a firewall?
A firewall can be defined as "a system or group of systems that enforces
an access control policy between two networks." In the context of
home networks, a firewall typically takes one of two forms:
Software firewall - specialized software running on an individual computer,
or a network firewall - a dedicated device designed to protect one or
more computers.
Both types of firewall
allow the user to define access policies for inbound connections to the
computers they are protecting. Many also provide the ability to control
what services (ports) the protected computers are able to access on the
Internet (outbound access). Most firewalls intended for home use come
with pre-configured security policies from which the user chooses, and
some allow the user to customize these policies for their specific needs.
Click
here for the ultimate in personal firewall software!
What does antivirus
software do?
There are a variety of antivirus software packages that operate in many
different ways, depending on how the vendor chose to implement their software.
What they have in common, though, is that they all look for patterns in
the files or memory of your computer that indicate the possible presence
of a known virus. Antivirus packages know what to look for through the
use of virus profiles (sometimes called "signatures") provided
by the vendor.
New viruses are discovered daily. The effectiveness of antivirus software
is dependent on having the latest virus profiles installed on your computer
so that it can look for recently discovered viruses. It is important to
keep these profiles up to date.
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