Cyclades PR1000 - Manual (Page 80)

80
Cyclades-PR1000
Chapter 11 - NAT
CHAPTER 11 NAT (NETWORK ADDRESS TRANSLATION)
NAT exists to convert local IP addresses into Internet “global” IP addresses. Internet IP addresses are assigned
by Internet providers. Due to the explosion of the internet, these numbers are scarce. Certain ranges of IP
addresses are reserved for internal use only — they may not have a direct connection to the Internet (for reference,
they are 10.0.0.0 - 10.255.255.255, 172.16.0.0 - 172.16.255.255, and 192.168.0.0 - 192.168.255.255). These
are used as local IP addresses. Figure 11.1 shows an example of the utility of NAT:
WWW
Server
Host
Global Address Range
- Network: 200.240.230.224
- Mask: 255.255.255.240
PR1000 With
Expanded NAT
PC 200.240.230.2
Router Ethernet Port
Primary IP Address: 192.168.0.1
Secondary IP Address: 200.200.200.1
200.200.200.10
200.200.200.11
192.168.0.5
Networks
192.168.0.0 &
200.200.200.0
Host
ftp
Server
192.168.0.31
192.168.0.30
FIGURE 11.1 NAT EXAMPLE
In this example, the company has:
• 14 global IP addresses available for NAT, 200.240.230.225 to 200.240.230.238,
• Two networks connected to the router via the Ethernet Interface, one of which will be translated,