ELSA LANCOM Wireless L-2 Manuel De L'utilisateur page 59

the actual information to be transmitted (useful data), the data packet also contains
address and control information.
IP address IP addresses are used in IP networks for communications between various devices. In
this case, every host has its own unique address by which it can be identified
unambiguously. What does an IP address look like? It comprises four bytes separated by
points, making a total of 32 bits. Each of the four bytes can take on values from 0 to 255,
e.g. 192.168.130.124.
To be precise, the IP address refers to the interface, and not the host itself. A terminal
device with more than one interface (such as a router) has to have an IP address at its
disposal for every single interface. This is why ISDN routers from ELSA for example,
have an IP address for communication with the hosts in their own network, as well as a
second IP address for communication with the "outside world" using the ISDN network.
In the same way, ELSA cable modems have an IP address for their own network and
another IP address for the exchange of data with the cable network.
Network
An IP address contains the address of the network as well as that of the host.The network
address
address is the same for all hosts on one network, whereas the address of the host is
exclusive and unique to the network. A router, for example, can have more than one IP
address, each one unique to the network.
Netmask How then can you differentiate between the part that determines the network and the
part that identifies the host? With the network mask. You all know what masks are: They
cover up one part of something and only allow the other part to be visible. This is exactly
how a network mask operates. It is a number which is identical in structure to the IP
address, i.e. 32 zeros or ones. The network mask usually starts with ones at the
beginning and ends with zeros. The zeros at the end thus cover the part of the IP address
which does not belong to the network address.
Examples:
This address...
IP-address
Netmask
Network address
The same IP address, this time with another netmask:
This address...
IP-address
Netmask
Network address
You can see from this that an IP address alone is not enough. A host can only be
identified unambiguously in combination with a netmask.
...in bytes... ...looks like this in bits:
192.168.120.253 11000000.10101000.01111000.11111101
255.255.255.0 11111111.11111111.11111111.00000000
192.168.120.0 11000000.10101000.01111000.00000000
...in bytes... ...looks like this in bits:
192.168.120.253 11000000.10101000.01111000.11111101
255.255.0.0 11111111.11111111.00000000.00000000
192.168.0.0 11000000.10101000.00000000.00000000
Technical basics
ELSA LANCOM Wireless
R7