ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Pobierz pdf (Strona 231)

There are two versions of the IP protocol: IPv4 and IPv6. The IPv4 address,

which is most frequently used nowadays, is on 4 bytes and only limited

functionalities are available, mainly centered on routing. IPv6 is an evolution of

IPv4 which is scarcely implemented in networks. Its address is on 16 bytes, and it

includes many functionalities, such as mobility, quality of service, and security man-

agement.

Structure of an IPv4 Address

The IPv4 address is on 4 bytes, i.e., 32 bits (1 byte is equivalent to 8 bits).

There are two parts in each IP address:

•

The network address;

•

A host number corresponding to the address of the computer itself.

Let us imagine a network consisting of three computers, the addresses of which

are 145.41.12.1, 145.41.12.2, and 145.41.12.3 respectively. In this case, the net-

work address is 145.41.12.x, 1, 2, and 3 corresponding to the host addresses of the

computers.

With such an addressing plan, the network can connect computers with

addresses between 145.41.12.1 and 145.41.12.254. 145.41.12.255 is a reserved

address, called “broadcast address,” which is used for sending information to all the

stations of the network. Such an addressing plan offers few possibilities in terms of

network connectivity, since it only addresses 254 potential computers.

Depending on the size of the network address, the number of networks and

therefore the number of associated hosts can be different. Address classes have been

defined to take this difference into account.

Address Classes

In IPv4, five address classes summarized in Table 9.4 have been defined.

These main address classes are defined according to the number of bytes used

for the network address:

•

For class A addresses, the first byte (8 bits) is reserved for the network address

with the first bit set to zero. Thus, the network address is included between

212 Configuration

Table 9.4 IPv4 Address Classes

ADDRESS ADDRESS RANGES

NUMBER OF

NETWORKS

NUMBER OF

HOSTS PER

NETWORK

Class A 1.0.0.0 to 126.0.0.0 126 16,777,214

Class B 128.0.0.0 to 191.255.0.0 16,384 65,534

Class C 192.0.0.0 to 223.255.255.0 2,097,152 254

Class D 224.0.0.0 to 225.0.0.0

Group addresses

(multicast)

Class E 225.0.0.0 to 240.0.0.0 Experimental

1 2 ... 226 227 228 229 230 231 232 233 234 235 236 ... 348 349

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