  The main reason for the standardization of network protocols, like QUIC, is
to ensure interoperability between implementations, which poses a challenging
task. Manual tests are currently used to test the different existing
implementations for interoperability, but given the complex nature of network
protocols, it is hard to cover all possible edge cases.
  State-of-the-art automated software testing techniques, such as Symbolic
Execution (SymEx), have proven themselves capable of analyzing complex
real-world software and finding hard to detect bugs. We present a SymEx-based
method for finding interoperability issues in QUIC implementations, and explore
its merit in a case study that analyzes the interoperability of picoquic and
QUANT. We find that, while SymEx is able to analyze deep interactions between
different implementations and uncovers several bugs, in order to enable
efficient interoperability testing, implementations need to provide additional
information about their current protocol state.
