The use of network applications for high availability systems requires the validation of its fault tolerance mechanisms to avoid unexpected behavior during execution. FIONA is a fault injection tool to experimentally validate these mechanisms of Java distributed applications. The tool uses JVMTI, a new interface for the development of debugging and monitoring tools that enables the instrumentation of Java applications. This approach provides complete transparency between the application under test and the fault injection tool, as well as portability. FIONA injects communication faults, making it possible to conduct the dependability evaluation of UDP based network protocols developed in Java.