ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka stáhnout pdf (Strana 255)

The disadvantage of this type of typology is that the PLC device only rarely has a

firewall used for blocking various traffic types and avoiding attacks on the network

or a VPN. In a topology where a dedicated computer is used for the Internet connec-

tion, any firewalling software or VPN server can be installed to protect the network.

Sharing the Internet Connection

For sharing an Internet connection, two protocols are used: the NAT (network

address translation) and the DHCP (dynamic host configuration protocol):

•

NAT enables the sharing of an Internet connection between several stations

while using the IP address given by the Internet access provider (IAP). Another

distinctive feature of the NAT is that this enables you to prevent certain

attacks. Some Internet modems fitted with router functionalities incorporate

the NAT, but it can be installed on a dedicated computer connected to the

Internet.

•

DHCP is a client-server protocol that enables you to dynamically allocate, for

a given amount of time (lease time), the TCP/IP parameters that a station

requires for its connection to the network. The parameters given by the DHCP

server to the station are the computer IP address, the subnet mask, the address

of the default gateway, and the addresses of the name servers (DNS). DHCP

236 PLC in the Home

Figure 10.20 Internet connection via a dedicated computer

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ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka Strana 255