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Glossary
A
Access Point.
A device that transports data between a wireless network and a wired network. With the help
of the system, a wireless base station is an example of an access point that acts between a wireless node
and with other wired PCs and peripherals.
D
Default Gateway.
A device that is placed between network segments (or “subnets”) to ensure that traffic is
properly routed between different subnets. To communicate with a device on another network, users need
to know the default gateway’s IP address.
DHCP (Dynamic Host Configuration Protocol).
A TCP/IP protocol that allows servers to assign IP
addresses dynamically to PCs and workstations. The PC or workstation “borrows” the IP address for a
period of time, then the IP address returns to the DHCP server for reassignment.
DMZ (Demilitarized Zone).
A computer or small subnetwork that sits between a trusted internal network
(such as a LAN), and an untrusted external network (such as the Internet). Typically, the DMZ contains
devices accessible to Internet traffic, such as Web (HTTP) servers, FTP servers, SMTP (e-mail) servers and
DNS servers.
DNS (Domain Name System).
The DNS is the way that Internet domain names (such as www.2wire.com)
are located and translated into IP addresses.
DSLAM (Digital Subscriber Line Access Multiplexer).
A device found in telephone company central offices
that takes a number of DSL subscriber lines and concentrates them onto a single ATM line.
E
Ethernet.
A type of local area network that operates over twisted wire and cable at speeds of up to 10
Mbps.
I
ICMP (Internet Control Message Protocol).
ICMP supports packets containing error, control, and
informational messages. For example, the PING command uses ICMP to test an Internet connection.
Although ICMP is generally harmless, there are some message types that should be dropped. Redirect (5),
Alternate Host Address (6), and Router Advertisement (9) can be used to redirect traffic from your site.
Echo (8), Timestamp (13), and Address Mask Request (17) can be used to obtain information on whether
the host is up, the local time, and the address mask used on your network, respectively. ICMP messages
are also sometimes used as part of DOS attacks (such as flood ping or ping of death).
Invalid TCP flags.
Combination of TCP flags (such as SYN/FIN) that signal a malicious attempt to get past
the firewall.
IP (Internet Protocol).
The standard signaling method used for all communication over the Internet.
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127
IP Address.
A numeric identifier for your computer. Just as the post office delivers mail to your home
address, servers know to deliver data to your computer based on your IP address. IP addresses can be
dynamic, meaning that your computer “borrows” the IP address for the necessary timeframe, or they can be
fixed, meaning that the number is permanently assigned to your computer.
L
LAN (Local Area Network).
A network connecting a number of computers to each other or to a central
server so that the computers can share programs and files.
M
MAC (Media Access Control) Address.
A hardware address that has been embedded into the network
interface card (NIC) by its vendor to uniquely identify each node, or point of connection, of a network.
Map to Host Port.
When set (not left blank or set to 0), this value provides the mapping offset to the local
computer. For example, if this value is set to 4000 and the range being opened is 100 to 108, the
forwarded data to the first value in the range will be sent to 4000. Subsequent ports will be mapped
accordingly; 101 will be sent to 4001, 102 will be sent to 4002, etc.
MTU (maximum transmission unit).
The largest size packet or frame, specified in octets (eight-bit bytes),
that can be sent from a computer to the network. The Internet's TCP uses the MTU to determine the
maximum size of each packet in any transmission. If the MTU is too large, the packet may need to be
retransmitted if it encounters a router that can't handle that large a packet. Too small an MTU size means
relatively more header overhead and more acknowledgements that have to be sent and handled. Most
computer operating systems provide a default MTU value that is suitable for most users. In general,
Internet users should follow the advice of their Internet service provider (ISP) about whether to change the
default value and what to change it to.
N
NAT (Network Address Translation).
Enables a LAN to use one set of IP addresses for internal traffic and a
second set of IP addresses for external traffic. This feature is used by the system so an end user can have
an internal computer network in their home, with all its computers using internal IP addresses, using only
one routable IP address, which accesses the outside (Internet).
P
PAT (Port Address Translation).
Allows hosts on a LAN to communicate with the rest of a network (such as
the Internet) without revealing their own private IP address. All outbound packets have their IP address
translated to the router’s external IP address. Replies come back to the router, which then translates them
back into the private IP address of the original host for final delivery.
PPP (Point-to-Point Protocol).
A protocol that allows a computer to access the Internet using a dial-up
phone line and a high-speed modem. This can be accomplished over Ethernet (PPPoE), or over
Asynchronous Transfer Mode (ATM; PPPoA).
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128
PPPoA (Point-to-Point Protocol over ATM).
A specification for connecting multiple computer users on an
Ethernet LAN to a remote site through common customer premises equipment (such as a modem). PPPoA
combines the Point-to-Point Protocol (PPP), commonly used in dialup connections, with the ATM
(Asynchronous Transfer Mode) protocol, which supports multiple users in a LAN.
PPPoE (Point-to-Point Protocol over Ethernet).
A specification for connecting multiple computer users on
an Ethernet LAN to a remote site through common customer premises equipment (such as a modem).
PPPoE combines the Point-to-Point Protocol (PPP), commonly used in dialup connections, with the Ethernet
protocol, which supports multiple users in a LAN.
Protocol Timeout.
The amount of time (in seconds) during which a connection in the specified range
remains open when there is no data transfer. After a connection has been established on a given port, the
sender and receiver usually determine when the session is finished and the connection is closed. However,
if the connection is left open and data transfer stops, the system must eventually close the connection and
reclaim the resources in order to protect your network. In some cases, the system might close the
application during normal operation (for example, if there is a long pause between data transfer). If this is
the case, lengthening the timeout may help.
PVC (permanent virtual circuit).
A virtual circuit that is permanently available. Used to establish
connections between hosts that communicate frequently.
R
Router.
The central switching device in a packet-switched computer network that directs and controls the
flow of data through the network.
S
Subnet Mask.
The IP addressing system allows subnetworks or “interchanges” to be created, and devices
numbers or “extensions” to be established within these subnetworks. These numbers are created using a
mathematical device called a subnet mask. A subnet mask, like the IP address, is a set of four numbers in
dotted decimal notation. Subnet masks typically take three forms:
255.0.0.0
255.255.0.0
255.255.255.0
The number 255 “masks” out the corresponding number of the IP address, resulting in IP address numbers
that are valid for the network. For example, an IP address of 123.45.67.89 and a subnet mask of
255.255.255.0 results in a sub network number of 123.45.67.0 and a device number of 89.
The subnet mask used for the network typically corresponds to the class of IP address assigned, as shown
in the following table.
IP Address Class
Dotted-Decimal Notation Ranges
Corresponding Subnet Mask
Class A
1.xxx.xxx.xxx to 126.xxx.xxx.xxx
255.0.0.0
Class B
128.0.xxx.xxx to 191.255.xxx.xxx
255.255.0.0
Class C
192.0.0.xxx to 223.255.255.xxx
255.255.255.0
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129
SYN Flood.
A method that the user of a hostile client program can use to conduct a denial-of-service (DOS)
attack on a computer server. The hostile client repeatedly sends SYN (synchronization) packets to every
port on the server, using fake IP addresses.
T
TCP/IP (Transmission Control Protocol/Internet Protocol).
A method of packet-switched data
transmission used on the Internet. The protocol specifies the manner in which a signal is divided into parts,
as well as the manner in which “address” information is added to each packet to ensure that it reaches its
destination and can be reassembled into the original message.
Transmission Control Protocol/Internet Protocol (TCP/IP).
See TCP/IP
.
U
UDP (User Datagram Protocol).
A TCP/IP protocol describing how data packets reach application programs
within a destination computer.
V
VPI (Virtual Path Identifier).
Identifier contained in the ATM cell header to designate the virtual path on the
physical ATM link.
VCI (Virtual Channel Identifier).
Identifier contained in the ATM cell header to designate the virtual channel
on the physical ATM link.
W
Wireless.
Transmission of data over radio waves rather than wiring.
Wireless channel.
The 2Wire gateway supports up to 13 wireless channels (based on country restrictions).
For example, the United States and Canada support channels 1 to 11; Europe and Australia support
channels 1 to 13.
In an 802.1b or 802.11g wireless network, data is transmitted at 2.5GHz. Wireless nodes communicate
with each other using radio frequency signals in the band between 2.4GHz and 2.5GHz. Neighboring
channels are 5 MHz apart; however, due to the spread spectrum effect of the signals, a node sending
signals using a particular channel will use frequency spectrum 12.5HHz above and below the center
channel frequency. As a result, two separate wireless networks using neighboring channels (for example,
channels 1 and 2) in the same general vicinity will interfere with each other. Applying two channels that
allow the maximum channel separation (such as channels 1 and 6, or channels 6 and 11) will provide a
noticeable performance increase over networks with minimal channel separation.
The radio frequency channels used in 802.11b/g networks are shown in the following table.
Channel
Range
Channel 1
2399.5 MHz - 2424.5 MHz
Channel 2
2404.5 MHz - 2429.5 MHz
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The preferred channel separation between the channels in neighboring wireless networks is 25 MHz (5
channels). This means that you can apply up to three different channels within your wireless network. There
are only 11 usable wireless channels in the United States. It is recommended that you start using channel
1 and expand to channel 6 (and 11 when necessary), as these three channels do not overlap.
Channel 3
2409.5 MHz - 2434.5 MHz
Channel 4
2414.5 MHz - 2439.5 MHz
Channel 5
2419.5 MHz - 2444.5 MHz
Channel 6
2424.5 MHz - 2449.5 MHz
Channel 7
2429.5 MHz - 2454.5 MHz
Channel 8
2434.5 MHz - 2459.5 MHz
Channel 9
2439.5 MHz - 2464.5 MHz
Channel 10
2444.5 MHz - 2469.5 MHz
Channel 11
2449.5 MHz - 2474.5 MHz
Channel 12
2454.5 MHz - 2479.5 MHz
Channel 13
2459.5 MHz - 2484.5 MHz
Channel
Range

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