Resource reservation protocol substitute reply router, resource reservation protocol substitute reply system and resource reservation protocol substitute reply method used in the same

A resource reservation protocol substitute reply router is provided for enabling execution of RSVP procedure as substitute by automatically detecting that a reception host does not support RSVP. A Path message storage portion stores a Path message handled by an RSVP control portion. An ICMP detecting portion monitors data packet input to a routing portion. When "message of Destination Unreachable" is found in the packet, an IP header information contained in the ICMP message and a stored value of the Path message storage portion are compared. If matched one is present, the ICMP message is disposed, and in place, it is requested to the substitute RSVP control portion to execute the procedure of RSVP on behalf of the reception host. The substitute RSVP control portion executes the procedure of RSVP on behalf of the original reception host.