[lwip-users] TCP state machine problem? LWIP 1.4.1

[Fabian Koch]

Hey all,

 

we had some weird behavior with a TCP connection on LWIP 1.4.1 when the peer (non-LWIP) has a cable disconnect:

 

• LWIP has an established TCP connection #1 running fine
• Peer has a cable disconnect
• Our application on top of LWIP runs into a receive timeout and closes the socket (500ms)
• Peer reconnects cable
• Our application opens a new connection #2 which again is established and running fine
• The FINACK+PSHACK re-sends of connection #1 also reaches the peer which answers RSTACK
• This keeps on looping until we restart the whole machine with LWIP

 

Also, I have a sort of “netstat” implemented on top of the LWIP socket API which runs over all possible sockets we have and if it finds a valid conn pointer there, prints infos (local addr, remot addr, port, TCP state and such). And connection #1 does not show up anymore in this view!

 

In my mind, the TCP state machine should be in FIN_WAIT_1 while the peer cable is disconnected?

And it should just jump to either CLOSED or TIME_WAIT when receiving the RSTs upon cable reconnect?

 

I attached a clipped pcap with only connection #1 shown and the problem starting at packet #19. Image the final exchange going on forever to understand the problem ;o)

 

Any comments or debugging ideas appreciated.

 

Kind regards

Fabian

 

LWIP_1_4_1_TCP_state.pcapng
Description: LWIP_1_4_1_TCP_state.pcapng