A probing method, arrangement, and system for estimating a condition, such as available bandwidth, of a data path in a communication network including multiple nodes are described. A probe-packet sender node transmits probe packets with a sent inter-packet separation and a time-to-live towards an intermediate node. Control message packets are generated by the intermediate node when the time-to-live expires. The probe-packet sender node receives the control message packets and calculates a received inter-packet separation. An estimate of the data path condition can be generated based on the sent inter-packet separation and the received inter-packet separation.