As the Digital Ecosystems are growing in use and in popularity, the need to boost the methods concerned by their interoperability is growing as well; making thus trustworthy interactions of the different agents (e.g. network systems) a priority. In our work, we focus on "soft trust", that is trust management systems that can be based on experience and reputation. Each trust system defines how they evaluate the trustee experience. The observations of the trustee behaviors are added to the trustee experience. Furthermore, most of the works dedicated to trust estimations in different kinds of ecosystems are based on local observations through monitored entities. No formal approaches have been defined for distributed monitored elements by considering several points of observations. This is what we intend in this work. We propose to use distributed network monitoring techniques to analyze the packets that the truster and trustee exchange in order to prove the trustee is acting in a trustworthy manner. A formal approach is defined to express trust properties and to evaluate them on real execution traces. Our approach is applied on DNS traces for assessing the trust among the entities