Netzob supports the expert in reverse engineering, evaluation, and simulation of communication protocols. Its main goals are to help security evaluators to assess the robustness of proprietary or unknown protocol implementations, simulate realistic communications to test third-party products (IDS, firewalls, etc.), and create an Open Source implementation of a proprietary or unknown protocol. Netzob provides a semi-automatic inferring process, and includes everything necessary to passively learn the vocabulary of a protocol and actively infer its grammar. The learnt protocol can afterward be simulated. Netzob handles text protocols (like HTTP and IRC), fixed field protocols (like IP and TCP), and variable field protocols (like ASN.1-based formats).