IP router device having a TCP termination function and a medium thereof

An IP router device, which has a function for terminating a TCP connection and for connecting a plurality of different IP networks, comprising:

• a first converting unit rewriting part of IP address information and port number information within a plurality of IP packets when the plurality of IP packets to be relayed, which form a TCP connection, pass through the router device;
• a unit extracting information indicating an original connection destination of the TCP connection, generating a TCP connection from the router to the connection destination, and linking the two TCP connections with streams;
• and
• a second converting unit rewriting part of IP address information and port number information within a plurality of IP packets forming a TCP connection for the TCP connection to the original connection destination, wherein
• said first and said second converting units handle the two TCP connections as a pair, store information needed for rewriting, which is related with a identification number, in a database by assigning a unique identification number to the pair, and manages the two TCP connections with the unique identification number stored in the database.