A network address conversion system for enabling access to a specific node
of a private network, having a private IP address, a method therefor, and
a recording medium for recording the method. The network address
conversion system includes a reservation unit for receiving an access
reservation demand from an external network node to access a specific
node of the private network, an external port value allocation unit for
allocating the external port value to the specific node, and transmitting
the external port value to the external network node, a mapping table for
storing the external port value, and an address conversion unit for
converting the external port value into a private IP address of the
specific node, when the external network node accesses the specific node
by using the external port value. As a result, the external network node
of the Internet can access the specific node of the private network,
having the private IP address.