Even if the benefit of implementing Software Product Lines is well established, adopting such a large system is still a complex choice to make: it is hard to implement, needs a good knowledge of market growth and a clear vision of the enterprise objectives for long term. Therefore, many companies remain unwilling to adopt such an approach, unless they gain flexibility and get guarantees. Flexibility can be achieved by adopting an Agile Software Product Line approach, to make sure changes are rapidly implemented and product adapted to market evolution. Guarantees can be acquired by tracing elements and the relations between them. However, tracing in Agile Software Product Line context still needs to gain maturity as it is costly and therefore rarely adopted. In this paper, we discuss the added value of traceability for Agile Software Product Lines, and present our tracing model inspired from dynamic network routing.