app-proxy compatibility option enable

By default, the application proxy compatibility option is disabled. The FW sends window update packets.

As an application proxy, the FW establishes a TCP connection with the server. The server determines whether the FW sends subsequent window update packets based on the ACK packet.

• If the TCP window field value in the ACK packet sent from the FW is 0, the server waits for subsequent window update packets from the FW.
  • If the server receives subsequent window update packets from the FW, traffic continues.
  • If the server does not receive window update packets from the FW, traffic between the server and FW is interrupted.
• If the TCP window field value in the ACK packet is not 0, the server does not wait for window update packets, and traffic continues.

On special networks where the FW sends window update packets to the server but the packets are discarded during transmission, the server interrupts traffic because it does not receive (should receive) window update packets, resulting in anomalies. To resolve this problem, you can run the app-proxy compatibility option enable command, so that the FW changes the TCP window field in the ACK packet to a non-0 value and does not send window update packets.