D-Link DFL-210 - NetDefend - Security Appliance, User Manual

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2. Specify a suitable name for the rule, for example NAT_HTTP
3. Now enter:
• Action: NAT
• Service: http
• Source Interface: lan
• Source Network: lannet
• Destination Interface: any
• Destination Network: all-nets
4. Under the NAT tab, make sure that the Use Interface Address option is selected
5. Click OK
Protocols Handled by NAT
Dynamic address translation is able to deal with the TCP, UDP and ICMP protocols with a good
level of functionality since the algorithm knows which values can be adjusted to become unique in
the three protocols. For other IP level protocols, unique connections are identified by their sender
addresses, destination addresses and protocol numbers.
This means that:
• An internal machine can communicate with several external servers using the same IP protocol.
• An internal machine can communicate with several external servers using different IP protocols.
• Several internal machines can communicate with different external servers using the same IP
protocol.
• Several internal machines can communicate with the same server using different IP protocols.
• Several internal machines can not communicate with the same external server using the same IP
protocol.
Note
These restrictions apply only to IP level protocols other than TCP, UDP and ICMP,
such as OSPF, L2TP, etc. They do not apply to the protocols transported by TCP,
UDP and ICMP such as telnet, FTP, HTTP and SMTP. NetDefendOS can alter port
number information in the TCP and UDP headers to make each connection unique,
even though such connections have had their sender addresses translated to the same
IP.
Some protocols, regardless of the method of transportation used, can cause problems during address
translation.
Anonymizing Internet Traffic with NAT
A useful application of the NAT feature in NetDefendOS is for anonymizing service providers to
anonymize traffic between clients and servers across the public Internet so that the client's public IP
address is not present in any server access requests or peer to peer traffic.
We shall examine the typical case where the D-Link Firewall acts as a PPTP server and terminates
the PPTP tunnel for PPTP clients. Clients that wish to be anonymous, communicate with their local
7.1. NAT Chapter 7. Address Translation
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