Patent ID: 8027246

Claim:
A network system, comprising: a plurality of node apparatuses each of which forms an aggregated link having a plurality of physical links, at least one of said plurality of node apparatuses comprising a storage unit in which a failure detection protocol, which monitors for communication line failure in the aggregated link formed by the node apparatus, is stored, and a control unit that executes the failure detection protocol, and wherein said control unit: stores each failure monitoring request for the aggregated link issued by a routing protocol in each requesting source, each failure monitoring request indicating a corresponding requesting source that issued the failure monitoring request and specifying a corresponding failure detection notification condition for the failure monitoring request, performs a failure monitoring operation on the aggregated link with each of the plurality of physical links of the aggregated link identified for each failure monitoring request, and for each failure monitoring request, when a communication failure on one or more of the physical links of the aggregated link is detected, checks the corresponding failure detection notification condition of the failure monitoring request in accordance with predetermined information provided in the failure monitoring request that specifies whether a notification is desired when a communication of all physical links of the aggregated link fails or a notification is desired when a communication of a specified number of physical links of the aggregated link fails, and, when the failure detection notification condition corresponding to the failure monitoring request is satisfied, sends a failure detection notification to the requesting source that issued the failure monitoring request.