A method for performing a link aggregation on a link aggregation group, comprising a plurality of transport links, for sessions received at a first network node which is connected to a second network node via the link aggregation group. The method, which is to be executed in the first network node, enables link aggregation optimization for the sessions destined for the second network node by selectively choosing transport link for the sessions on the basis of the load of the transport links. The suggested link aggregation results in a packet load balancing and improved bandwidth utilization. An arrangement suitable for executing the suggested method is also provided.