Network (L3/L4) filters

The API for network level filters is relatively simple since ultimately the filters operate on raw bytes and a small number of connection events (e.g., TLS handshake complete, connection disconnected locally or remotely, etc.). Filters in the chain can stop and subsequently continue iteration to further filters. This allows for more complex scenarios such as calling a , etc. Envoy already includes several network level filters that are documented in this architecture overview as well as the configuration reference.