[NCLUG] debugging ftp iptables

[Matt Rosing]

I have a strange problem with uploading ftp from one particular laptop 
(a windows box) to one particular server (windows again) through my 
iptables firewall. I'm stuck with using ftp as it's part of an application.

-It hangs. When I look at the packets through my firewall the server 
sends back RST packets as soon as the client sends data.
-download works fine, only upload fails.
-I can upload from my laptop to other servers fine.
-I can upload from other machines behind my firewall to that server 
fine, although another winodws box was rather slow doing it.
-I can upload a small file from my laptop to the server just fine (536 
bytes works, 537 fails). The file I'm trying to upload is 2500 bytes.
-I tried connecting my laptop directly to my cable modem and it uploaded 
fine.
-I installed filezilla on my laptop and it failed on that file until I 
throttled the upload rate to 2kB/sec and then it worked.
-Passive or active from my linux machine doesn't matter. I don't know 
how to do passive from windows.
-I upgraded my firewall to the most recent Debian stable.

The history is that this worked fine on my laptop using my current 
firewall. I had a hard drive failure on my laptop and had to reload 
everything. I had windows 7 on it before and put windows 7 pro on it. 
But it used to have vista on it and I went back to that and tried it and 
it still fails.

I looked at the packets to and from the server and the only odd thing I 
saw was that packets from machines that work had len=576 and from my 
laptop it was 596.

So what do I need to do to figure this out?

Thanks

Matt