Just for a small detail: do you always observe the problem or does it occur
more often when the system is under load (multiple FTP clients connected)? Did
you check if the buffer allocated to lwIP was getting full (mostly, the TCP
buffer chains getting filled)? This reminds me of an issue I had had
before...
----- Original Message -----
Sent: Friday, November 23, 2007 4:11
PM
Subject: [lwip-users] Dup ACKs and window
updates during FTP session
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.
Also, as you can see from the attached Ethereal trace there
are a number of window updates. Is this normal?
I hope someone can suggest whether there is anything untoward
with this behaviour, and if so, where I might start looking for the
reason.
Many thanks in anticipation for any help you can give.
Kind regards,
Clive Wilson
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