D-Link NetDefend DFL-210 User Manual page 206

7.1. Dynamic Network Address
Translation
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 server 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.
Some protocols, regardless of the method of transportation used, can cause problems during address
translation.
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 "protocols" transported by TCP, UDP
and ICMP such as telnet, FTP, HTTP, SMTP, etc. 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.
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Chapter 7. Address Translation