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#1 2010-06-30 09:38 PM

dcoder
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Registered: 2010-06-30
Posts: 7

Re: Need help on retransmission and RST.

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#2 2010-06-30 09:58 PM

RobSeace
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From: Boston, MA
Registered: 2002-06-12
Posts: 3,839
Website

Re: Need help on retransmission and RST.

I don't see any screenshot or dump attached...  (If possible, the actual raw pcap file
would be preferred; we can load that into wireshark ourselves, and see the whole
traffic session...)

Well, "iptables" is the just the user-space app that interfaces with the kernel firewall
features ("netfilter")...  So, it's not a server, really...  But, yeah, you could have some
firewall rules in place on the Linux box that's causing problems...  You (or whoever is
in control of it) should take a look at the current rules in place, and possibly try
temporarily disabling them all for testing purposes, just to see if they're responsible...

But, it sounds like one of your packets gets lost somewhere enroute and you try to
resend it...  Not sure why you'd get the RST...  Unless maybe the server is really
multiple servers behind some kind of load-sharing system or something, and you
switch which real server you're talking to part-way through your connection...  Do you
have any tech details on this server?  Is it on your LAN or remote across the Net?  Do
you know the local network setup for it?

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#3 2010-06-30 10:12 PM

dcoder
Member
Registered: 2010-06-30
Posts: 7

Re: Need help on retransmission and RST.

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#4 2010-06-30 10:31 PM

dcoder
Member
Registered: 2010-06-30
Posts: 7

Re: Need help on retransmission and RST.

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#5 2010-07-01 02:07 PM

RobSeace
Administrator
From: Boston, MA
Registered: 2002-06-12
Posts: 3,839
Website

Re: Need help on retransmission and RST.

Wow, you've got a TON of "TCP checksum incorrect" errors there!  But, I'm guessing
they must just be due to checksum offloading to the NIC or something, so wireshark
is just not seeing the correct checksums...  Because, the packets do seem to get
sent and replied to, so they must be alright eventually...

Ok, what seems to happen is you send 3 packets: 92 bytes with seq# 1, 1380 bytes
with seq# 93, and 324 bytes with seq# 1473...  The server ACKs the first one...  Then,
you send another packet of 1380 bytes with seq# 1797, and THEN 3 seconds later,
you resend your second packet with seq# 93 (which is perfectly reasonable, since
the server has still only ACKed your first so far), and then you get the strange RST
that ACKs your second packet and seems to include a duplicate copy of its data...
No idea what the cause would be...  Unless it really is something like load-balancing
among multiple real server machines all sharing that same IP...  Because, it definitely
seems like your network connection to the server has gotten lost somehow, since it's
not ACKing anything other than your first packet...  So, by the time you resend the
second one again, you may be talking to a different server at that same IP...

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#6 2010-07-02 05:38 PM

dcoder
Member
Registered: 2010-06-30
Posts: 7

Re: Need help on retransmission and RST.

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#7 2010-07-02 09:01 PM

RobSeace
Administrator
From: Boston, MA
Registered: 2002-06-12
Posts: 3,839
Website

Re: Need help on retransmission and RST.

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#8 2010-07-06 10:19 PM

dcoder
Member
Registered: 2010-06-30
Posts: 7

Re: Need help on retransmission and RST.

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#9 2010-07-06 10:38 PM

RobSeace
Administrator
From: Boston, MA
Registered: 2002-06-12
Posts: 3,839
Website

Re: Need help on retransmission and RST.

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#10 2010-07-06 11:25 PM

i3839
Oddministrator
From: Amsterdam
Registered: 2003-06-07
Posts: 2,239

Re: Need help on retransmission and RST.

Perhaps there are two NICs with the same MAC address on the network.
Wild guess and not very likely, but it might be something to keep in mind.

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