IP NAT Bidirectional (Two-Way/Inbound) Operation
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Facilitating Inbound NAT Using DNS
There only two methods to resolve the hidden address problem. One is to use static mapping for devices like servers on the inside network that need to be accessed from the outside. When static mapping is employed, the global address of the device that is using the static mapping will be publicly known, which solves the where do I send my request to problem.
The other solution is to make use of the TCP/IP Domain Name System (DNS). As explained in detail in the section on DNS, this protocol allows requests to be sent as names instead of IP addresses; the DNS server translates these names to their corresponding addresses. It is possible to integrate DNS and NAT so they work together. This process is described in RFC 2694, DNS extensions to Network Address Translators (DNS_ALG).
In this technique, an outside device can in fact make use of dynamic mapping. The basic process (highly simplified) is as follows:
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