Network Mask - Hirschmann RS20 User Manual

Entering the IP Parameters
0 Net ID - 7 bits
I 0 Net ID - 14 bits
I I 0 Net ID - 21 bits
I I I 0 Multicast Group ID - 28 bits
I I I I reserved for future use - 28 b its
Figure 7: Bit representation of the IP address
An IP address belongs to class A if its first bit is a zero, i.e. the first decimal
number is less than 128. The IP address belongs to class B if the first bit is a
one and the second bit is a zero, i.e. the first decimal number is between 128
and 191. The IP address belongs to class C if the first two bits are a one, i.e.
the first decimal number is higher than 191.
Assigning the host address (host id) is the responsibility of the network oper-
ator. He alone is responsible for the uniqueness of the IP addresses he as-
signs.

2.1.2 Network mask

Routers and gateways subdivide large networks into subnetworks. The net-
work mask assigns the IP addresses of the individual devices to a particular
subnetwork.
The division into subnetworks with the aid of the network mask is performed
in much the same way as the division of the network addresses (net id) into
classes A to C.
In bits of the host address (host id) that represent the mask are set to one.
The remaining bits of the host address in the network mask are set to zero
(see the following examples).
28
Host ID - 24 bits
Class A
Host ID - 16 bits
Class B
Host ID - 8 bit s
Class C
Class D
Class E
2.1 IP Parameter Basics
Basic Configuration L2P
Release 4.2 07/08