Gateway apparatus, packet forwarding method, and program

Abstract

The present invention provides a gateway apparatus and a packet forwarding method for rewriting the application header of a forwarded packet without terminating a TCP connection between a client and a server. For that purpose, the gateway apparatus in accordance with the present invention uses the conversion sectionof the gateway moduleto register, in a conversion table, a pair of a sequence number (Seq#) which is expected to be contained in the TCP header of a next packet to forward and a Seq# after conversion which is obtained by considering a change in packet size due to application (AP) header rewriting as a pair of an expected Seq# and a conversion Seq# as well as a pair of an expected Ack# and a conversion Ack# contained in the TCP header of a packet in a direction opposite to that of the previously forwarded packet at the time of forwarding. Then, the conversion sectionrefers to the conversion tableat next packet forwarding to rewrite the Seq# and the Ack# contained in the TCP header of a packet to forward to the conversion Seq# and conversion Ack# corresponding to the expected Seq# and expected Ack# matching these numbers.