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Glossary
Network mask / Subnet
mask
Port number
PPPoE
PPTP
146
A company network with access to the Internet is normally officially
assigned only a single IP address, e.g. 134.76.0.0. In this example
address it can be seen from the 1st byte that this company network is
a Class B network, i.e. the last 2 bytes can be used freely for host
addressing. Arithmetically that represents an address space of 65,536
possible hosts (256 x 256).
Such a huge network is not very practical. It is necessary here to form
subnetworks. This is done using a subnet mask. Like an IP address,
this is a field 4 bytes long. The value 255 is assigned to each of the
bytes that represent the network address. The main purpose of this is
to "hide" a part of the host address range in order to use it for the
addressing of subnetworks. For example, in a Class B network (2
bytes for the network address, 2 bytes for the host address), by means
of the subnet mask 255.255.255.0 it is possible to take the 3rd byte,
which was actually intended for host addressing, and use it now for
subnet addressing. Arithmetically that means that 256 subnets with
256 hosts each could be created.
The Port Number field is a 2-byte field in UDP and TCP headers. The
assignment of port numbers serves to identify various data flows that
are processed simultaneously by UDP/TCP. The entire data exchange
between UDP/TCP and the application processes takes place via
these port numbers. The assignment of port numbers to application
processes is performed dynamically and randomly. Fixed port numbers
are assigned for certain frequently-used application processes. These
are called Assigned Numbers.
Acronym for Point-to-Point Protocol over Ethernet. It is based on the
standards PPP and Ethernet. PPPoE is a specification for connecting
users to the Internet via Ethernet using a jointly used broadband
medium such as DSL, Wireless LAN or cable modem.
Acronym for Point-to-Point Tunneling Protocol. This protocol was
developed by Microsoft, U.S. Robotics and others in order to transmit
data securely between two VPN nodes ( VPN) over a public network.
SINAUT MD741-1
C79000-G8976-C236-05
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