Router network, with saving function, for subordinate LAN at router fault

A router network comprising:

• a plurality of local area networks, between which data communications are performed using an Internet protocol or internetwork packet protocol;
• and
• a plurality of routers, each having input/output line sections for inputting and outputting internet protocol packets with a form corresponding to a specification for a media, to which a router is connected, and a table, on which a network environment is set for subordinate segments serviced by a specific router,
• wherein the network environment set for subordinate segments serviced by the specific router is copied to be set on a different table at a different router in advance, as well as a different network environment is set for subordinate segments serviced by the different router on the different table, and
• wherein when a fault occurs at the specific router, the different router is used as a proxy router to provide communication support for the subordinate segments on behalf of the specific router as well as for the subordinate segments for the different router in accordance with the network environment set on the different table.