Network system comprising a plurality of lans connected to an ISDN via a plurality of routers, each capable of automatically creating a table for storing router information

A method of creating a table included in each of first through N-th routers for connecting a plurality of LANs (Local Area Networks ) via an ISDN ( Integrated Services Digital Network) in a network system where N represents a predetermined natural number which is not less than three, said LANs being divided into first through N-th LAN groups which are connected to said first through said N-th routers, respectively, each of said first through said N-th LAN groups comprising at least one of said LANs, an n-th router being for connecting an n-th LAN group through said ISDN with at least one of said first through said N-th LAN groups except for said n-th LAN group, where n represents each of 1 through N, the table of said n-th router being for storing router information in connection with all of said first through said N-th routers except for said n-th router, said method comprising the steps of:

• setting, in said n-th router, local router information indicative of an n-th router IP (Internet Protocol) address and an n-th router telephone number both of which are assigned to said n-th router;
• setting, in said n-th router, n-th main/sub setting information indicating that said n-th router should be operable as either a main router or one of sub-routers, whereby a particular one of said first through said N-th routers is operable as said main router while remaining routers except for said main router are operable as said sub-routers;
• setting, in each of said sub-routers, main router information indicative of a main router IP address and a main router telephone number both of which are assigned to said main router;
• writing, each of said sub-routers, said main router information in said table;
• sending, from each of said sub-routers to said main router, an enquiry packet including said local router information on the basis of said main router information stored in said table;
• receiving, in said main router, said enquiry packet from each of said sub-routers;
• entering, in said main router, the local router information included in said enquiry packet in said table;
• sending, from said main router to each of said sub-routers, a reply packet including the local router information stored in said table;
• receiving, in each of said sub-routers, said reply packet from said main router;
• and
• entering, in each of said sub-routers, the local router information included in said reply packet in said table.