Virtual Router makes TCP

[RolandMinde]

1. A TCP port forwarding is configured.
2. The guest system is running.
3. The application on the guest system, normally listening on this port, is not running.
4. Trying a TCP connection from outer network succeeds.
5. After sending the first message over this connection, the connection is closed from partner site.

This behavior seems incorrect, because a router supports level 3 and may not serve level 4 TCP connections. The expected behavior is an instant rejection of the connection establishment.

[Valery Ushakov]

Is it NAT or NAT Network? Does the reset happen if the client doesn't send any data immediately after the connection is established?

Note that "NAT" is a bit of misnomer, it's not really NAT, so the incoming connection is always accepted, but if the guest is not listening, the established connection will be immediately reset.

[RolandMinde]

Replying to vushakov:

Is it NAT or NAT Network?

It is NAT Network

Does the reset happen if the client doesn't send any data immediately after the connection is established?

No, the reset comes after sending of data; but this may be an effect of the Java Virtual Maschine of my Java program.

[Valery Ushakov]

I guess by "reset comes" you mean that Java reports the reset to the program when the program tries to send some data. The actual reset should have come immediately after connection. Unfortunately this is an inherent limitation.