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Glossary
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Hub
A hub is a place of convergence where data
arrives from one or more directions and is
forwarded out in one or more directions. It
usually includes a switch of some kind. It
connects an Ethernet bridge/router to a group
of PCs on a LAN and allows communication
to pass between the networked devices.
ICMP – Internet Control Message Protocol
An Internet protocol used to report errors and
other network-related information. The ping
command makes use of ICMP.
IGMP – Internet Group Management
Protocol
IGMPis defined in RFC 1112 as the standard
for IP multicasting in the Internet.
It's used to establish host memberships in
particular multicast groups on a single
network. The mechanisms of the protocol
allow a host to inform its local router, using
Host Membership Reports, that it wants to
receive messages addressed to a specific
multicast group.
IP address
The address of a host (computer) on the
Internet, consisting of four numbers, each
from 0 to 255, separated by periods, e.g.
192.168.1.1. An IP address consists of a
network ID that identifies the particular
network the host belongs to, and a host ID
uniquely identifying the host itself on that
network. A network mask is used to define
the network ID and the host ID. Because IP
addresses are difficult to remember, they
usually have an associated domain name that
can be specified instead.
ISP – Internet Service Provider
A company that provides access to the
Internet.
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LAN – Local Area Network
A computer network limited to the immediate
area, such as a home, office, or small
building.
LED – Light Emitting Diode
A type of control lamp on devices that
indicates the status of the device.
MAC address
Short for Media Access Control address, the
permanent hardware address of a device
assigned by its manufacturer. MAC
addresses are expressed as six pairs of hex
characters (0-9 and A-f), with each pair
separated by colons. For example:
1a:2b:23:5b:66:9a
NAT - Network Address Translation
A service performed by many routers that
translates your network's publicly known IP
address into a private IP address for each
computer on your LAN. Only your router and
your LAN know these addresses; the outside
world sees only the public IP address when
talking to a computer on your LAN.
Network mask
A network mask is a sequence of bits applied
to an IP address to select the network ID
while ignoring the host ID. Bits set to 1 mean
"select this bit" while bits set to 0 mean
"ignore this bit". For example, if the network
mask 255.255.255.0 is applied to the IP
address 100.10.50.1, the network ID is
100.10.50, and the host ID is 1.
NIC – Network Interface Card
An adapter card that plugs into your computer
and provides the physical interface to your
network cabling, which for Ethernet NICs is
tyically an RJ-45 connector.
Packet
Data transmitted on a network consists of
units called packets. Each packet contains a
payload (the data), plus overhead information
1553-ZAT 759 94 Uen B – July 2005
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