id	summary	reporter	owner	description	type	status	component	version	resolution	keywords	cc	guest	host
17556	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.
"	defect	closed	network/NAT	VirtualBox 5.2.6	wontfix			Linux	Windows