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EtherFast
®
Cable/DSL VPN Router with 4-Port 10/100 Switch
Cable Modem
- A device that connects a computer to the cable television net-
work, which in turn connects to the Internet. Once connected, cable modem
users have a continuous connection to the Internet. Cable modems feature
asymmetric transfer rates: around 36 Mbps downstream (from the Internet to
the computer), and from 200 Kbps to 2 Mbps upstream (from the computer to
the Internet).
CAT 5
- ANSI/EIA (American National Standards Institute/Electronic
Industries Association) Standard 568 is one of several standards that specify
"categories" (the singular is commonly referred to as "CAT") of twisted pair
cabling systems (wires, junctions, and connectors) in terms of the data rates
that they can sustain. CAT 5 cable has a maximum throughput of 100 Mbps and
is usually utilized for 100BaseTX networks.
Default Gateway
- The routing device used to forward all traffic that is not
addressed to a station within the local subnet.
DES
(
D
igital
E
ncryption
S
tandard) - Encryption used for data communication
where both the sender and receiver must know the same secret key, used to
encrypt and decrypt the data, or to generate and verify a message authentica-
tion code. Linksys DES encryption uses a 56-bit key.
DHCP
(
D
ynamic
H
ost
C
onfiguration
P
rotocol) - A protocol that lets network
administrators manage centrally and automate the assignment of Internet
Protocol (IP) addresses in an organization's network. Using the Internet's set of
protocol (TCP/IP), each machine that can connect to the Internet needs a
unique IP address. When an organization sets up its computer users with a con-
nection to the Internet, an IP address must be assigned to each machine.
Without DHCP, the IP address must be entered manually at each computer and,
if computers move to another location in another part of the network, a new IP
address must be entered. DHCP lets a network administrator supervise and dis-
tribute IP addresses from a central point and automatically sends a new IP
address when a computer is plugged into a different place in the network.
DHCP uses the concept of a "lease" or amount of time that a given IP address
will be valid for a computer. The lease time can vary depending on how long a
user is likely to require the Internet connection at a particular location. It's espe-
cially useful in education and other environments where users change fre-
quently. Using very short leases, DHCP can dynamically reconfigure networks
in which there are more computers than there are available IP addresses.
105
Instant Broadband
®
Series
Appendix H: Glossary
3DES
- 3DES is a variation on DES that uses a 168-bit key.
Adapter
- Printed circuit board that plugs into a PC to add to capabilities or
connectivity to a PC. In a networked environment, a network interface card is
the typical adapter that allows the PC or server to connect to the intranet and/or
Internet.
AppleTalk
- An Apple Computer networking system that supports Apple's pro-
prietary local talk.
Auto-negotiate
- To automatically determine the correct settings. The term is
often used with communications and networking. For example, Ethernet
10/100 cards, hubs and switches can determine the highest speed of the node
they are connected to and adjust their transmission rate accordingly.
Boot
- To cause the computer to start executing instructions. Personal comput-
ers contain built-in instructions in a ROM chip that are automatically executed
on startup. These instructions search for the operating system, load it and pass
control to it.
Broadband
- A data-transmission scheme in which multiple signals share the
bandwidth of a medium. This allows the transmission of voice, data and video
signals over a single medium. Cable television uses broadband techniques to
deliver dozens of channels over one cable.
Browser
- A browser is an application program that provides a way to look at
and interact with all the information on the World Wide Web or PC. The word
"browser" seems to have originated prior to the Web as a generic term for user
interfaces that let you browse text files online.
Buffer
- A buffer is a shared or assigned memory area used by hardware
devices or program processes that operate at different speeds or with different
sets of priorities. The buffer allows each device or process to operate without
being held up by the other. In order for a buffer to be effective, the size of the
buffer and the algorithms for moving data into and out of the buffer need to be
considered by the buffer designer. Like a cache, a buffer is a "midpoint hold-
ing place" but exists not so much to accelerate the speed of an activity as to
support the coordination of separate activities.
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EtherFast
®
Cable/DSL VPN Router with 4-Port 10/100 Switch
Firewall
- A firewall is a set of related programs, located at a network gateway
server, that protects the resources of a network from users from other networks.
(The term also implies the security policy that is used with the programs.) An
enterprise with an intranet that allows its workers access to the wider Internet
installs a firewall to prevent outsiders from accessing its own private data
resources and for controlling what outside resources to which its own users
have access.
Basically, a firewall, working closely with a router, examines each network
packet to determine whether to forward it toward its destination.
Firmware
- Code that is written onto read-only memory (ROM) or program-
mable read-only memory (PROM).
Once firmware has been written onto the
ROM or PROM, it is retained even when the device is turned off.
FTP
(
F
ile
T
ransfer
P
rotocol) - A protocol used to transfer files over a TCP/IP
network (Internet, UNIX, etc.). For example, after developing the HTML pages
for a Web site on a local machine, they are typically uploaded to the Web serv-
er using FTP.
FTP includes functions to log onto the network, list directories and copy files.
It can also convert between the ASCII and EBCDIC character codes. FTP oper-
ations can be performed by typing commands at a command prompt or via an
FTP utility running under a graphical interface such as Windows. FTP transfers
can also be initiated from within a Web browser by entering the URL preceded
with ftp://.
Unlike e-mail programs in which graphics and program files have to be
"attached," FTP is designed to handle binary files directly and does not add the
overhead of encoding and decoding the data.
Full Duplex
- The ability of a device or line to transmit data simultaneously in
both directions.
Gateway
- A device that interconnects networks with different, incompatible
communications protocols.
Half Duplex
- Data transmission that can occur in two directions over a single
line, but only one direction at a time.
Hardware
- Hardware is the physical aspect of computers, telecommunica-
tions, and other information technology devices. The term arose as a way to dis-
107
Instant Broadband
®
Series
DHCP supports static addresses for computers containing Web servers that
need a permanent IP address.
DMZ
(
D
e
m
ilitarized
Z
one) - Allows one IP address (or computer) to be
exposed to the Internet.
Some applications require multiple TCP/IP ports to be
open.
You should set your computer with a static IP address if you want to use
DMZ Hosting.
DNS
- The domain name system (DNS) is the way that Internet domain name
are located and translated into Internet Protocol (IP) addresses. A domain name
is a meaningful and easy-to-remember "handle" for an Internet address.
Domain
- A subnetwork comprised of a group of clients and servers under the
control of one security database. Dividing LANs into domains improves per-
formance and security.
Download
- To receive a file transmitted over a network. In a communications
session, download means receive, upload means transmit.
DSL
(
D
igital
S
ubscriber
L
ine) - A technology that dramatically increases the
digital capacity of ordinary telephone lines into the home or office and, by
employing unused bandwidth, still allows for normal phone usage. DSL pro-
vides "always-on" operation, eliminating the need to dial in to the service.
Dynamic IP Address
- An IP address that is automatically assigned to a client
station in a TCP/IP network, typically by a DHCP server. Network devices that
serve multiple users, such as servers and printers, are usually assigned static IP
addresses.
Dynamic Routing
- The ability for a router to forward data via a different route
based on the current conditions of the communications circuits. For example,
it can adjust for overloaded traffic or failing lines and is much more flexible
than static routing, which uses a fixed forwarding path.
Encryption
- A security method that applies a specific algorithm to data in
order to alter the data's appearance and prevent other devices from reading the
information.
Ethernet
- Standard network protocol that specifies how data is placed on and
retrieved from a common transmission medium. Has a transfer rate of 10 Mbps.
Forms the underlying transport vehicle used by several upper-level protocols,
including TCP/IP and XNS.
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EtherFast
®
Cable/DSL VPN Router with 4-Port 10/100 Switch
IPSec
(
I
nternet
P
rotocol
S
ecurity) - A suite of protocols used to implement
secure exchange of packets at the IP layer. IPSec supports two basic modes:
Transport and Tunnel.
Transport encrypts the payload of each packet, leaving
the header untouched, while Tunnel mode encrypts both the header and the pay-
load and is therefore more secure.
IPSec must be supported on both transmit-
ter and receiver and must share a public key.
Tunnel mode is widely deployed
in VPNs (Virtual Private Networks).
IPX
(
I
nternetwork
P
acket E
X
change) - A NetWare communications protocol
used to route messages from one node to another. IPX packets include network
addresses and can be routed from one network to another.
ISP
(
I
nternet
S
ervice
P
rovider) - A company that provides individuals and
companies access to the Internet and other related services such as Web site
building and virtual hosting.
LAN
(
L
ocal
A
rea
N
etwork) - A group of computers and associated devices that
share a common communications line and typically share the resources of a
single processor or server within a small geographic area (for example, within
an office building).
MAC
(
M
edia
A
ccess
C
ontrol)
Address
- A unique number assigned by the
manufacturer to any Ethernet networking device, such as a network adapter,
that allows the network to identify it at the hardware level.
Mbps
(
M
ega
b
its
p
er
s
econd) - One million bits per second; unit of measure-
ment for data transmission.
MD5
- A type of one-way authentication method that uses passwords. MD5
authentication is not as secure as the EAP-TLS or EAP/TTLS authentication
methods.
MIB
(
M
anagement
I
nformation
B
ase) - A set of database objects. This set con-
tains information about a specific device for utilizing SNMP.
mIRC
- mIRC runs under Windows and provides a graphical interface for log-
ging onto IRC servers and listing, joining and leaving channels.
Multicasting
- Sending data to a group of nodes instead of a single destination.
109
Instant Broadband
®
Series
tinguish the "box" and the electronic circuitry and components of a computer
from the program you put in it to make it do things. The program came to be
known as the software.
Hop
- The link between two network nodes.
HTTP
(
H
yper
T
ext
T
ransport
P
rotocol) - The communications protocol used
to connect to servers on the World Wide Web. Its primary function is to estab-
lish a connection with a Web server and transmit HTML pages to the client
browser.
Hub
- The device that serves as the central location for attaching wires from
workstations. Can be passive, where there is no amplification of the signals; or
active, where the hubs are used like repeaters to provide an extension of the
cable that connects to a workstation.
ICQ
- A conferencing program for the Internet that provides interactive chat,
e-mail and file transfer and can alert you when someone on your predefined list
has also come online.
IKE
(
I
nternet
K
ey
E
xchange) - A negotiation and key exchange protocol spec-
ified by the Internet Engineering Task Force. An IKE security association (SA)
automatically negotiates encryption and authentication keys. With IKE, an ini-
tial exchange authenticates the VPN session and automatically negotiates keys
that will be used to pass encrypted data over the Internet or any other network.
IP
(
I
nternet
P
rotocol) - The method or protocol by which data is sent from one
computer to another on the Internet. It is a standard set of rules, procedures, or
conventions relating to the format and timing of data transmission between two
computers that they must accept and use to be able to understand each other.
IP Address
- In the most widely installed level of the Internet Protocol (IP)
today, an IP address is a 32-binary digit number that identifies each sender or
receiver of information that is sent in packet across the Internet. When you
request an HTML page or send e-mail, the Internet Protocol part of TCP/IP
includes your IP address in the message (actually, in each of the packets if more
than one is required) and sends it to the IP address that is obtained by looking
up the domain name in the Uniform Resource Locator you requested or in the
e-mail address you're sending a note to. At the other end, the recipient can see
the IP address of the Web page requestor or the e-mail sender and can respond
by sending another message using the IP address it received.
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EtherFast
®
Cable/DSL VPN Router with 4-Port 10/100 Switch
Ping
(
P
acket
IN
ternet
G
roper) - An Internet utility used to determine whether
a particular IP address is online. It is used to test and debug a network by send-
ing out a packet and waiting for a response.
POP3
(
P
ost
O
ffice
P
rotocol
3
) - A standard mail server commonly used on the
Internet. It provides a message store that holds incoming e-mail until users log
on and download it. POP3 is a simple system with little selectivity. All pending
messages and attachments are downloaded at the same time. POP3 uses the
SMTP messaging protocol.
Port
- A pathway into and out of the computer or a network device such as a
switch or router. For example, the serial and parallel ports on a personal com-
puter are external sockets for plugging in communications lines, modems and
printers.
PPPoE
(
P
oint to
P
oint
P
rotocol
o
ver
E
thernet) - PPPoE is a method for the
encapsulation of PPP packets over Ethernet frames from the user to the ISP
over the Internet.
One reason PPPoE is preferred by ISPs is because it provides
authentication (username and password) in addition to data transport.
A PPPoE
session can be initiated by either a client application residing on a PC, or by
client firmware residing on a modem or router.
PPTP
(
P
oint-to-
P
oint
T
unneling
P
rotocol) - A protocol which allows the Point
to Point Protocol (PPP) to be tunneled through an IP network. PPTP does not
specify any changes to the PPP protocol but rather describes a "tunneling serv-
ice" for carrying PPP (a tunneling service is any network service enabled by
tunneling protocols such as PPTP, L2F, L2TP, and IPSEC tunnel mode). One
example of a tunneling service is secure access from a remote small office net-
work to a headquarters corporate intranet via a Virtual Private Network (VPN)
that traverses the Internet. However, tunneling services are not restricted to
corporate environments and may also be used for personal (i.e., non-business)
applications.
RIP
(
R
outing
I
nformation
P
rotocol) - A simple routing protocol that is part of
the TCP/IP protocol suite. It determines a route based on the smallest hop count
between source and destination. RIP is a distance vector protocol that routine-
ly broadcasts routing information to its neighboring routers.
RJ-45
(
R
egistered
J
ack-
45
) - A connector similar to a telephone connector that
holds up to eight wires, used for connecting Ethernet devices.
111
Instant Broadband
®
Series
NAT
(
N
etwork
A
ddress
T
ranslation) - The translation of an Internet Protocol
address (IP address) used within one network to a different IP address known
within another network. One network is designated the inside network and the
other is the outside.
NetBIOS
- The native networking protocol in DOS and Windows networks.
Although originally combined with its transport layer protocol (NetBEUI),
NetBIOS today provides a programming interface for applications at the ses-
sion layer (layer 5). NetBIOS can ride over NetBEUI, its native transport,
which is not routable, or over TCP/IP and IPX/SPX, which are routable proto-
cols.
NetBIOS computers are identified by a unique 15-character name, and
Windows machines (NetBIOS machines) periodically broadcast their names
over the network so that Network Neighborhood can catalog them. For TCP/IP
networks, NetBIOS names are turned into IP addresses via manual configura-
tion in an LMHOSTS file or a WINS server.
There are two NetBIOS modes. The Datagram mode is the fastest mode, but
does not guarantee delivery. It uses a self-contained packet with send and
receive name, usually limited to 512 bytes. If the recipient device is not listen-
ing for messages, the datagram is lost. The Session mode establishes a connec-
tion until broken. It guarantees delivery of messages up to 64KB long.
Network
- A system that transmits any combination of voice, video and/or data
between users.
Network Mask
- Also known as the "Subnet Mask".
Node
- A network junction or connection point, typically a computer or work
station.
Notebook
(PC) - A notebook computer is a battery-powered personal comput-
er generally smaller than a briefcase that can easily be transported and conve-
niently used in temporary spaces such as on airplanes, in libraries, temporary
offices, and at meetings. A notebook computer, sometimes called a laptop com-
puter, typically weighs less than five pounds and is three inches or less in thick-
ness.
Packet
- A unit of data routed between an origin and a destination in a network.
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EtherFast
®
Cable/DSL VPN Router with 4-Port 10/100 Switch
orous inspection, stateful packet inspection closes off ports until connection to
the specific port is requested. This allows an added layer of protection from the
threat of port scanning.
Static IP Address
- A permanent IP address that is assigned to a node in an IP
or a TCP/IP network.
Static Routing
- Forwarding data in a network via a fixed path. Static routing
cannot adjust to changing line conditions as can dynamic routing.
Subnet Mask
- The method used for splitting IP networks into a series of sub-
groups, or subnets. The mask is a binary pattern that is matched up with the IP
address to turn part of the host ID address field into a field for subnets.
Switch
- 1. A data switch connects computing devices to host computers,
allowing a large number of devices to share a limited number of ports. 2. A
device for making, breaking, or changing the connections in an electrical cir-
cuit.
TCP
(
T
ransmission
C
ontrol
P
rotocol) - A method (protocol) used along with
the IP (Internet Protocol) to send data in the form of message units (datagram)
between network devices over a LAN or WAN. While IP takes care of handling
the actual delivery of the data (routing), TCP takes care of keeping track of the
individual units of data (called packets) that a message is divided into for effi-
cient delivery over the network. TCP is known as a "connection oriented" pro-
tocol due to requiring the receiver of a packet to return an acknowledgment of
receipt to the sender of the packet resulting in transmission control.
TCP/IP
(
T
ransmission
C
ontrol
P
rotocol/
I
nternet
P
rotocol) - The basic com-
munication language or set of protocols for communications over a network
(developed specifically for the Internet).
TCP/IP defines a suite or group of
protocols and not only TCP and IP.
TFTP
(
T
rivial
F
ile
T
ransfer
P
rotocol) - A version of the TCP/IP FTP protocol
that has no directory or password capability.
Throughput
- The amount of data moved successfully from one place to
another in a given time period.
UDP
(
U
ser
D
atagram
P
rotocol) - A method (protocol) used along with the IP
(Internet Protocol) to send data in the form of message units (datagram)
between network devices over a LAN or WAN. While IP takes care of handling
113
Instant Broadband
®
Series
Router
- Protocol-dependent device that connects subnetworks together.
Routers are useful in breaking down a very large network into smaller subnet-
works; they introduce longer delays and typically have much lower throughput
rates than bridges.
Security Association
- A group of security settings related to a specific VPN
tunnel.
Server
- Any computer whose function in a network is to provide user access
to files, printing, communications, and other services.
SMTP
(
S
imple
M
ail
T
ransfer
P
rotocol)
- The standard e-mail protocol on the
Internet. It is a TCP/IP protocol that defines the message format and the mes-
sage transfer agent (MTA), which stores and forwards the mail.
SNMP
(
S
imple
N
etwork
M
anagement
P
rotocol)
- A widely used network
monitoring and control protocol. Data is passed from SNMP agents, which are
hardware and/or software processes reporting activity in each network device
(hub, router, bridge, etc.) to the workstation console used to oversee the net-
work. The agents return information contained in a MIB (Management
Information Base), which is a data structure that defines what is obtainable
from the device and what can be controlled (turned off, on, etc.).
Software
- Instructions for the computer. A series of instructions that performs
a particular task is called a "program." The two major categories of software are
"system software" and "application software." System software is made up of
control programs such as the operating system and database management sys-
tem (DBMS). Application software is any program that processes data for the
user.
A common misconception is that software is data. It is not. Software tells the
hardware how to process the data.
SPI
(
S
tateful
P
acket
I
nspection) - A firewall technology that monitors the state
of the transaction so that it can verify that the destination of an inbound pack-
et matches the source of a previous outbound request. It examines not just the
headers of the packet, but also the contents, to determine more about the pack-
et than just its source and destination information. It is called "stateful" because
verifies that the stated destination computer has previously requested the cur-
rent communication. In this way, it verifies that all communications are initiat-
ed by the recipient computer and are taking place only with sources that are
known and trusted from previous interactions. In addition to being a more rig-
112
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