AVM FRITZ-Box-Fon-WLAN-7570 Router Manual PDF (Setup & Configuration Guide)

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Glossary

Especially effective firewalls go even further, analyzing and

evaluating the contents of the packets and filtering them

according to prescribed rules. Such techniques are includ-

ed in a Stateful Packet Inspection Firewall, for instance.

Firmware

The firmware is saved in programmable components within

a device. Through the possibility of updating the firmware

by computer at any time, manufacturers enjoy great flexibil-

ity in reacting to the demands of the operational environ-

ment, integrating new functions requested by customers,

and eliminating errors discovered after production.

Fixed IP address

Fixed IP addresses are IP addresses which are permanently

assigned to a computer or another device like a network

printer.

Assigning fixed IP addresses makes sense in cases where a

local network has a sufficiently large pool of IP addresses

available, or when a computer is always supposed to be ac-

cessible at a certain address (such as a web server or an e-

mail server).

FTP

abbreviation for File Transfer Protocol

The File Transfer Protocol allows files to be exchanged be-

tween two computers operating in the Internet. Data ex-

change takes place via an FTP server and what is known as

an FTP client. The more convenient FTP clients are available

as stand-alone software or are components of some ISDN

data transfer software; simple FTP clients are now included

in many web browsers.

Gateway

Gateway is a general term designating an interface between

two computer networks. Such a network interface can be

realized using a router or a bridge, for instance.

If a computer wants to transfer data packets to a computer

in another network, it must first transmit the packet to the

gateway. To do this, the computer must know the address

of the gateway.

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Glossary

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147

If all packets that cannot be delivered in a local network al-

ways are to be transmitted to their given recipients via the

same gateway, for this purpose the address of the gateway

must be saved as the default gateway in the network con-

figuration of the computer.

Such a default gateway for the computer is negotiated auto-

matically by the operating system or the dialing software

whenever an ISDN-Controller or DSL-Controller establishes

a connection to the Internet. If a router is used for the

shared Internet access in a local network, the IP address of

the router must be entered as the default gateway in the

TCP/IP configuration of each computer that wishes to use

the Internet connection. If the TCP/IP configuration is per-

formed by means of a DHCP server, there is no need to en-

ter the gateway address manually.

abbreviation for Internet Protocol

The IP Internet Protocol is the most important basic proto-

col for the control of data exchange in local networks and in

the Internet. The Internet protocol works without a connec-

tion; in other words, data packets are transmitted from the

sender to the recipient without previous consultation. The

addresses of the recipient and the sender in the data pack-

ets are given as IP addresses.

IP address

abbreviation for Internet Protocol address

In IP-based networks, for instance in the Internet and local

networks, all connected devices are addressed via their IP

addresses. So that data packets are sure to be delivered to

the right address, each IP address may be assigned only

once within the Internet or a local IP network.

The IP address consists of four three-digit groups of num-

bers (for instance, 192.168.178.247). Each group of num-

bers can assume values between 000 and 255.

Every IP address contains two components: the network ad-

dress and the host address. These two components can be

read out of an IP address only if the subnet mask is also

specified.

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Glossary

IP addresses can be public or private, and also fixed or as-

signed dynamically. See the corresponding entries in the

glossary for more information.

IP addressing

Addressing is one of the main functions of the Internet Pro-

tocol (IP). Internet addresses can be written in decimal, oc-

tal or hexadecimal notation. The FRITZ!Box uses “dotted-

decimal” notation: The four bytes of an address are repre-

sented by decimal numbers separated by dots. The total

volume of Internet addresses, the address space, is sepa-

rated into classes (A, B, C, D, and E). The full set of IP ad-

dresses, called the address space, is grouped into address

classes designated as A, B, C, D and E. Only the first three

of these five address classes are actually used. These

classes can be described as follows:

Properties of IP Address Classes

Every IP address consists of two parts: the network address

and the host address. The sizes of the network address and

the host address are variable, and determined by the first

four bits (of the first byte) of the IP address.

IP masquerading

By means of IP masquerading a computer or LAN can be

protected from unauthorized connection request from the

Internet. Masquerading works by converting the IP address-

es used in a network to one public IP address. From the out-

side it appears that all requests are sent from a single com-

puter.

Classes

Properties

Network Address,

Decimal Value

Class A ad-

dress

Few networks, many hubs

0-127

Class B ad-

dress

Intermediate distribution of

networks and hubs

128-191

Class C ad-

dress

Many networks, few hubs

192-223

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Glossary

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IP network

A network in which data exchange takes place on the basis

of the Internet Protocol is called an IP network.

Port

So that a single network connection on a connection can be

used by multiple applications to exchange data with re-

mote sites at the same time, a computer administers what

are known as ports for the IP-based protocols TCP and UDP.

Ports substantiate the point of access for the data packets

delivered via the IP Internet protocol. While the IP address

determines the destination computer quite generally, the

port addresses the communication interface provided by

an application for a certain communication procedure.

The Internet protocol allots 16 bits for the specification of

the port number. Thus a total of 65,535 different port num-

bers can be specified. Ports up to port number 1,024 are re-

served for special system applications and typical Internet

applications. These include, for instance, the port numbers

21 for FTP (File Transfer Protocol), 25 for SMTP (Simple Mail

Transfer Protocol), 53 for DNS (Domain Name Service) and

80 for HTTP (Hypertext Transfer Protocol).

Ports are primarily of interest to users for their role in pro-

tecting an Internet connection from external attacks. Most

firewalls offer the possibility of preventing data traffic on

certain ports. This means that certain port numbers can be

blocked to prevent data from being delivered to system ser-

vices. This is also a way of preventing any Trojans (mali-

cious applications opening backdoors on a computer) that

may have infected your computer from receiving data on

ports it created as means of accessing your computer for

potentially damaging activities. A firewall blocks most atyp-

ical port numbers not required for normal operation of an

application and offers specialized users the opportunity to

forward specified ports.

Port forwarding

With port forwarding it is possible to specify ports that will

allow all incoming or outgoing data packets to pass through

a router or firewall.

If a computer from the local network offers server services,

for instance, the configuration of a router using NAT or IP

masquerading must forward the port used by the server

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Glossary

service for access to incoming data packets and thus keep

it open permanently. The private IP address of the given

computer must be saved as the destination address for all

of the packets arriving at the port.

Typical server applications which require port forwarding

are FTP and Web servers. To allow access to a computer via

remote management software like Symantec’s pcAnywhere

or Microsoft’s Remote Desktop, or even use of a file-sharing

program like eDonkey, the required ports must be released

for port forwarding. Port forwarding settings for the most

important application cases are quite simple as long as the

settings of the router or the firewall already contain rules

with a corresponding preconfiguration.

Private IP

address

Private IP addresses are used for computers and other net-

work devices within local IP networks.

Since many local IP networks are not connected to the In-

ternet except via single computers or routers (gateway), cer-

tain address ranges are excluded from the publicly availa-

ble IP addresses so that they are available for assignment

in local IP networks. An IP address may only be assigned

once within the local network. A private IP address may ex-

ist in any number of other local networks.

Public IP

address

A public IP address is an IP address valid in the Internet. Ev-

ery computer or router participating in the Internet must

have a uniquely assigned public IP address. This address is

usually negotiated dynamically with the Internet Service

Provider when a connection to the Internet is dialed. The In-

ternet Service Provider assigns the negotiated IP address to

the computer or router for the duration of an Internet ses-

sion.

Subnetwork

A local IP network can consist of one subnetwork or be di-

vided into multiple subnetworks. The division into subnet-

works is performed when the local IP network is configured.

The subnetworks of a local IP network are also IP networks.

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