Distributed event routing on the top of overlay networks has emerged as a key technology for achieving scalable information dissemination. In particular it has been used as preferential communication backbone within publish/ subscribe communication system. Its aim is to reduce the network and computational overhead per event diffusion to a set (possibly large) of interested recipients despite churn and subscription changes. This talk points out the functional decomposition between event-based routing layer, the overlay infrastructure layer (structured and unstructured) and the network protocols layer. Hence the talk surveys solutions for event based routing on overlay infrastructures discussing their inherent limitations and constraints related to both the process of arrival and departure of nodes from the overlay network and the process of subscription changes at the application level.