# Firewall A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. Firewalls establish a barrier between trusted internal networks and untrusted external networks, such as the internet. Firewalls operate at different layers of the network stack. Packet-filtering firewalls inspect individual packets based on IP addresses and ports. Stateful firewalls track the state of network connections. Application-layer firewalls (also called Web Application Firewalls or WAFs) inspect the content of HTTP requests and can block attacks like SQL injection, cross-site scripting, and request forgery. In API management, WAFs are commonly deployed alongside or integrated into API gateways. They inspect API requests for malicious payloads, enforce rate limits on suspicious traffic, and block known attack patterns. Cloud-based WAFs provided by platforms like Cloudflare can protect API endpoints without requiring any changes to backend infrastructure, filtering malicious traffic at the edge before it reaches origin servers. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.serverlessapigateway.com/glossary/f/firewall.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.