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Cyclades-PR4000
Chapter 13 - NAT
CHAPTER 13 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. 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
PR4000 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,
• Two servers that are accessed via the same global IP address, assigned statically.