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D.1.2 Network Address Translation (NAT)
Traditionally, multiple PCs that needed simultaneous Internet access also required a
range of IP addresses from the Internet Service Provider (ISP). Not only was this
method very costly, but the number of available IP addresses for PCs is limited.
Instead, BiGuard 2/10 uses a type of address sharing called Network Address
Translation to grant Internet access to several PCs on the same network through the
same Internet account. This method translates internal IP addresses to a single
address that is unique on the Internet. This unique address can either be fixed or
dynamic, depending on the type of Internet account, and the internal LAN IP
addresses may also be either private or registered addresses.
NAT also offers firewall-like protection to your network, since internal LAN
addresses are shielded from the public Internet. All incoming traffic to the public IP
address is handled by the router, which means added security for your network from
intruders. If a particular PC on your LAN requires access from outside PCs, you can
use port forwarding to accomplish this. For information on how to configure port
forwarding on BiGuard 2/10, refer to the Virtual Server section of Chapter 4:
Router Configuration.
D.1.3 Dynamic Host Configuration Protocol (DHCP)
If the PCs on a LAN require access to the Internet, each PC must be configured with
an IP address, a gateway address, and one or more DNS server addresses. Rather
than configuring each PC manually, you can instead configure a network device to
act as a Dynamic Host Configuration Protocol (DHCP) server. PCs on the network can
automatically obtain IP addresses from a list of addresses stored on the DHCP server.
In addition, other information such as gateway and DNS address can also be
assigned with a DHCP server. When connecting to the ISP, BiGuard 2/10 also
functions as a DHCP client. BiGuard 2/10 can automatically obtain an IP address,
subnet mask, gateway address, and DNS server addresses if the ISP assigns this
information via DHCP.
D.2 Router Basics
D.2.1 What is a Router?
A router is a device that forwards data packets along networks. A router is