Draytek Vigor130, User Manual

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Vigor130 Series User’s Guide 48
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Local Area Network (LAN) is a group of subnets regulated and ruled by modem. The design
of network structure is related to what type of public IP addresses coming from your ISP.
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The most generic function of Vigor modem is NAT. It creates a private subnet of your own.
As mentioned previously, the modem will talk to other public hosts on the Internet by using
public IP address and talking to local hosts by using its private IP address. What NAT does is
to translate the packets from public IP address to private IP address to forward the right
packets to the right host and vice versa. Besides, Vigor modem has a built-in DHCP server
that assigns private IP address to each local host. See the following diagram for a briefly
understanding.
In some special case, you may have a public IP subnet from your ISP such as
220.135.240.0/24. This means that you can set up a public subnet or call second subnet that
each host is equipped with a public IP address. As a part of the public subnet, the Vigor
modem will serve for IP routing to help hosts in the public subnet to communicate with other
public hosts or servers outside. Therefore, the modem should be set as the gateway for public
hosts.