The present invention relates to a method, system and router device for determining resources in an IP-based network, wherein a probe functionality is provided at a specific router device (90) located in a predetermined area (RA) of the IP-based network (50). When a link state change is detected in the specific router device (90), the probe functionality (P) forwards a list of router devices located in the predetermined area (RA) to a resource managing function which then requests at least one of a topology information and a link information from the router devices indicated in the list. Thereby, the resource information at the resource managing function can be kept updated at reduced signaling load and fast response times due to the fact that resource information is requested only from predetermined areas and at times of change.