Stateful functions are functions that keep some internal state across invocations, allowing them to retain information from previous executions. This is in contrast to stateless functions, which do not preserve any information between calls and always behave in the same way regardless of how many times they are called. In networking, stateful functions play a crucial role in ensuring proper communication, security, and efficient data transfer. They are used to monitor connections, manage active sessions, and maintain information about the status of network activities. This helps provide continuity, reliability, and control over traffic and resources. This thesis focuses on stateful firewalls, a key application of stateful functions.