Re: NAT dropping FIN ACK from remote server

[Florian Westphal <fw@strlen.de>]

vDev <vijaypas@gmail.com> wrote:
> I am experiencing a problem with Linux as a NAT router. A host/client
> on the private LAN establishes a TCP connection to a server on the WAN
> (Internet) through the Linux/NAT router. Here's what happens when
> client attempts to tear down the socket.
> 
> 1. Client on private LAN opens a TCP connection to the remote server
> on the public network through Linux/NAT router.
> 2. Client exchanges data with the remote server.
> 3. The server closes the TCP connection by sending a FIN to the
> client. Linux/NAT router successfully forwards the FIN to the client.
> 4. The client now sends an ACK to FIN to the remote host, which is
> forwarded by the Linux/NAT router to the server.
> 5. The client then sends a FIN to the remote host, which is forwarded
> by the Linux/NAT router to the remote server.
> 6. The server now sends an ACK to the client. THE Linux/NAT router
> DOES NOT FORWARD THE ACK TO THE CLIENT. GETS DROPPED!

Any chance to get a tcpdump of such a connection?
(Dumping on the interface in direction of the server, so we can see
 the server ACK that is being dropped).