TCP connection killed is not detected inside Guest in NAT mode

[Pdufrene]

I have the following configuration

A windows PC (IP address 192.168.10.200) running EchoTool Server (​http://bansky.net/echotool/) on port 8080 Launch by command line: echotool /p tcp /s 8080

Another Windows PC (windows 7 64Bit) (IP address 192.168.10.70) acting as Virtualbox Host (version 4.1.2) On this PC a VM is running (Guest Windows XP Pro) with network card in NAT mode and IP address set to 192.168.101.15

Inside the VM I launch a telnet session to the EchoTool server by doing telnet 192.168.10.200 8080

The echo is working fine.

Then I kill the EchoTool Server. The TCP RST frame is well received by the Host by not sent to the guest. So the telnet client do not detect the connection lost.

More strange is that if the telnet client send another TCP frame this frame is acknowledged (See attached Wireshark log).

Inside Telnet_Guest.pcap file the EchoTool server is running between from frames 1 to 8. Between frame 8 and 9 the server is killed. And after when the telnet client send a frame (nb 9 and 11) they are acknowledged by frames 10 and 12. but this frames are not visible on Host Wireshark traces (see Telnet_Host.pcap). The acknowledged frames seems to be generated by the NAT engine itself.

It seems that there is no way for the Guest to detect that the connection is lost.

[Pdufrene]

Telnet_Guest.pcap

[Pdufrene]

Telnet_Host.pcap

[Pdufrene]

VBox.log

[aeichner]

Please reopen if still relevant with a recent VirtualBox release.