Dup ACKs and window updates during FTP sessionHello, Clive
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...
Cheers
S. Ali Tokmen
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----- Original Message -----
From: Wilson, Clive
To: '[email protected]'
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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