1. Field of the Invention
The present invention relates to a method for transferring path or routing information of internetworking equipment, such as a router, brouter (which serves both as a bridge and a router), etc., which is connected to communication circuits and communicates path or routing information between networks. Throughout the following description and claims, the terms "path" and "routing" are used interchangeably.
2. Description of the Related Art
Conventionally, internetworking equipment (e.g., routers) of this type are connected to communication circuits, such as public networks, ISDNs (integrated services digital networks), etc. In order to enable data communication between the networks, the routers carry out propagation and control of path information (routing information) in the networks. Protocols for the propagation of the routing information include dynamic routing protocols, such as an RIP (routing information protocol). The routers request periodical transmission of all pieces of routing information according to the RIP, to thereby exchange the routing information between the networks.
This routing method requires a function (hereinafter referred to as "periodical update function") to make a simple path calculation from information for routers to execute a gateway operation for data next and from metric information indicative of the number of the routers (including a local one) and transmit all pieces of routing information periodically (e.g., once in 30 seconds), and a function (hereinafter referred to as "age-out function") to erase the router information and metric information when there is no data input for a predetermined period of time. Besides the periodical update function, the routing method covers a function (hereinafter referred to as "triggered update function") to transmit only changed routing information, if any, immediately.
With use of the RIP, according to the routing information method described above, all pieces of routing information need not be set statically, so that change of the routing information attributable to disconnection of the path can be automatically tackled with speed. In some cases, the routers based on this routing method may carry out routing by utilizing a timer-charged circuit, such as an ISDN. Preferably, in these cases, the connection time for the circuit should be minimized so that the circuit can be internetworked only when necessary.
When periodical updating is carried out, the circuit is frequently internetworked for periodical transmission, and sometimes may be left internetworked. In the case where the routing is effected with use of the timer-charged ISDN, therefore, a method is conventionally used such that the routing information is statically set to ensure practical costs.
In general, the routing information can be set statically in a very simple network arrangement (including one or two networks). In the least intricate network arrangement (including three or more networks), however, the routing information cannot be easily set without good knowledge of networks.
Conventionally, therefore, routing protocols are not expected to use the periodical update function. In this case, the purpose of application requires the circuit to be disconnected when there is no communication, and information is held without time-out control. Further, the routing protocols are bound to be worked only in specific circuits between specific routers.
According to this routing method, however, the information can be transmitted only a specific number of times, so that it is expected to be delivered correctly to destination routers without fail during the transmission. Once the information is subjected to mismatching, moreover, it cannot be restored with ease, so that the utmost care should be taken to avoid such mismatching. In case of mismatching, furthermore, the information must be able to be restored.
When the routing information is changed, triggered updating is normally effected such that the information is transmitted immediately. In the case of an interface which has no broadcast function (broadcast-type general message receiving function), e.g., an interface such that the partners of internetworking are changed by the source of transmission using an ISDN, however, a triggered update is transmitted to all the partners, so that the routers are subjected to a substantial load. In the case where the number of partners of transmission is large, in particular, the load on the routers is a great problem.