# Pre-Filter *** The Prefilter is designed for application-specific attacks. It enforces strict TCP/UDP authentication. New TCP clients must perform their initial TCP handshake twice: once to the DDoS Filters, after which the DDoS Filters transparently forward the session. The Filters send the scrubbed traffic directly to generic mitigation. It also scrubs UDP traffic for some games/applications, which you can see in the list below. Any UDP traffic flows permanently through the filters. The traffic is then sent back to the generic mitigation. Please note: Sessions that are created only a few seconds after the threshold is reached can still be dropped. --- # 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.packets-decreaser.net/ddos-protection/layer-4/how-we-mitigate-ddos-attacks/pre-filter.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.