[lwip-users] strange problems (small etherreal log attached)

[Bonny Gijzen]

Hi,

 

As you may know I am running a client using lwIP, but sometimes I have some problems.

 

I have made an etherreal log of the connection (on the servers side) and I can see some oddities
near the end, like missing segment, retransmissions and duplicate ack's.

(The 82. is my clients IP, the 192. is the servers IP)

www.ic-prog.com/mylog_eth.rar

 

I am not very familiar with TCP internals, but still I tried to analyze the log.

This is what I have noticed:

 

1) As you can see I send the same message every 10 seconds

(This I have done on purpose to make debugging easier)

 

2) At some point (near the end of the log) I can see a 20 second gap between messages.

This means that 1 msg from my client (lwip) has not reached the server.

The server notices this (because the seq doesn't match) and reacts to that.

 

In this log the missing frame was detected 10 seconds later (at the time my client had sent a new msg).

This is wrong because lwip would need to see an ACK and if not a retransmission should kick in much earlier.

(I am not sure about the timeframe used here, but should be millisecs I guess)

 

I have checked my lwIP timers, they are OK.

(I use a 250msec interval for tcp_tmr() which invokes both the fast and slow timer)

 

I have tried to simulate this at home, with unplugging the ethernet connector.

This does trigger the rexmit() call (and backoff value was incremented each timeout period).

When plugging the connector back in everything seemed to continue as normal.

 

**********

 

I hope someone can take a look at this log, specially at the oddities near the end

and perhaps write a small explanation of what (he thinks) is happening.

Thanks for your support and a nice stack :-)

 

Rgs Bonny