On Fri, 2007-11-23 at 09:11 -0600, Wilson, Clive wrote: > Hello, > > I'm using LwIP v1.1.0 and am having a few problems with > retransmissions and duplicate ACKs, and hope someone might be able to > offer some advice. > > I'm using LwIP to drive an FTP client over a dial-up PPP connection. > This is connected to a Windows 2000 server RAS machine, running > Filezilla FTP server. However, I don't think the network interface is > necessarily important here. > > I am transferring files in both directions, but the area of concern is > in retrieving files from the FTP server. > > I have attached an Ethereal trace of the complete session. What I am > seeing are packet retransmissions and duplicate ACKs between LwIP (IP > address 192.168.123.5) and the FTP server (192.168.123.4). > Interestingly, it seems to be fairly repeatable: I always seem to get > the packet containing "226 Transfer OK" retransmitted after the > 25KByte file transfer. I also get a duplicate ACK a few packets later. > Also, if I make the transferred file larger (say 200KBytes) I will see > multiple retransmits and dup ACKs - but only at the end of the file > transfer, not during it.
The only thing that is particularly odd is the repeatability. In the trace you supply packet 165 is a retransmission of 160. It shouldn't have been necessary to retransmit because packet 161 ACKs packet 160. However, if the ACK was lost or delayed then a single retransmission like this is harmless and to be expected. The duplicate ACK will be a consequence of the retransmission being received, and is again OK. Also, the retransmission is done by the non-lwIP end, so the only way that lwIP could be at fault is if the ACK were somehow corrupt, which it doesn't seem to be. Window updates are normal. Kieran _______________________________________________ lwip-users mailing list [email protected] http://lists.nongnu.org/mailman/listinfo/lwip-users
