Glossary of Terms
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D-Link NetDefend firewall User Guide
level of security by examining every
layer within a packet, unlike other
systems of inspection. Stateful
Inspection extracts information
required for security decisions from
all application layers and retains this
information in dynamic state tables
for evaluating subsequent connection
attempts. In other words, it learns!
Subnet Mask
A 32-bit identifier indicating how
the network is split into subnets. The
subnet mask indicates which part of
the IP address is the host ID and
which indicates the subnet.
T
TCP
TCP (Transmission Control
Protocol) is a set of rules (protocol)
used along with the Internet Protocol
(IP) to send data in the form of
message units between computers
over the Internet. While IP takes care
of handling the actual delivery of the
data, TCP takes care of keeping
track of the individual units of data
(called packets) that a message is
divided into for efficient routing
through the Internet.
For example, when an HTML file is
sent to you from a Web server, the
Transmission Control Protocol
(TCP) program layer in that server
divides the file into one or more
packets, numbers the packets, and
then forwards them individually to
the IP program layer. Although each
packet has the same destination IP
address, it may get routed differently
through the network.
At the other end (the client program
in your computer), TCP reassembles
the individual packets and waits until
they have arrived to forward them to
you as a single file.
TCP/IP
TCP/IP (Transmission Control
Protocol/Internet Protocol) is the
underlying communication protocol
of the Internet.
U
UDP
UDP (User Datagram Protocol) is a
communications protocol that offers
a limited amount of service when
messages are exchanged between
computers in a network that uses the
Internet Protocol (IP). UDP is an
alternative to the Transmission
Control Protocol (TCP) and, together
with IP, is sometimes referred to as
UDP/IP. Like the Transmission
Control Protocol, UDP uses the
Internet Protocol to actually get a
data unit (called a datagram) from
one computer to another. Unlike