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Private IP Addresses
When isolated from the Internet, the hosts on your local network may be assigned IP addresses
with no conflicts. However, the Internet Assigned Numbers Authority (IANA) has reserved sev-
eral blocks of IP addresses for private networks. These include:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.16.255.255 192.168.0.0 - 192.168.255.255
When assigning IP addresses to your private network, be sure to use IP addresses from these
ranges.
Network Address Translation (NAT)
Traditionally, multiple computers 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 computers is limited. Instead, BiGuard S10
uses a type of address sharing called Network Address Translation to grant Internet access to
several computers on the same network through the same Internet account. This method trans-
lates 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 computer on
your LAN requires access from outside computers, you can use port forwarding to accomplish
this. For information on how to configure port forwarding on BiGuard S10, refer to
Configuring
the Virtual Server
on page
54
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 Con-
figuration 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 gate-
way and DNS address can also be assigned with a DHCP server. When connecting to the ISP,
BiGuard S10 also functions as a DHCP client. BiGuard S10 can automatically obtain an IP
address, subnet mask, gateway address, and DNS server addresses if the ISP assigns this
information using DHCP.
Router Basics
What is a Router?
A router is a device that forwards data packets along networks. A router is connected to at least
two networks. Usually, this is a LAN and a WAN that is connected to an ISP network. Routers
are located at gateways, the places where two or more networks connect. Routers use headers
and forwarding tables to determine the best path for forwarding the packets, and they use proto-
cols to communicate with each other and configure the best route between any two hosts.
Routers can vary in performance and scale, the types of physical WAN connection they support,
and the number of routing protocols supported. BiGuard S10 offers a convenient and powerful
way for small-to-medium businesses to connect their networks.