ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Pobierz pdf (Strona 233)

Subnet Mask

The mask is used for knowing the network address of a computer via a binary sub-

traction between the mask and the computer IP address.

If the IP address of a computer is 192.168.0.1 and if the 255.255.255.0 mask is

applied to it, the binary subtraction of these two addresses gives 192.0.0.0, i.e., the

network address.

In general, the masks for class A, class B, and class C addresses are 255.0.0.0,

255.255.0.0, and 255.255.255.0, respectively.

During mask configuration for two computers, if the IP address of one of them is

192.168.1.1 with the 255.255.255.0 mask and if the IP address of the second one is

192.168.1.10 with the 255.225.0.0 mask, their network addresses (192.168.0.x and

192.168.1.x) are not identical. Therefore, they do not belong to the same network

and cannot communicate.

DNS (Domain Name Service)

DNS is a hierarchical structure consisting of a group of servers used for associating

an IP address with a domain name consisting of an organization name (e.g., Google)

and a classification (.fr, .com, and so forth).

In this way, it is much easier to remember Web site, messaging, or FTP addresses

rather than their associated IP address.

It is still possible to know the IP address of a particular server or of a Web site.

For example, the IP address of the www.google.com Web site can be found out just

by ping-ing to this site as illustrated in Figure 9.39.

In general, two DNS server addresses are requested when the network parame-

ters are configured in order to allow access to the network, should a server be defec-

tive. DNS addresses are necessarily IP addresses.

214 Configuration

Figure 9.39 IP address of www.google.com

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ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Strona 233