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FTP data is identified as window update in Wireshark

Posted on 2011-09-14
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Last Modified: 2012-06-21
In the expert info composite screen the ftp data packets show up as windows update?

Group        Protocol     Summary                Count
Sequence  TCP            Window Update     37856

Is this normal? Does the wireshark dissector not identify FTP data correctly?

Or do I have a lot of windows update traffic on the network?
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Question by:Dragon0x40
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Accepted Solution

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netjgrnaut earned 500 total points
ID: 36539309
A TCP Window Update packet should not be confused with a "Microsoft Windows Update" packet (which Wireshark wouldn't identify as such, anyway).

Explanation from http://ask.wireshark.org/questions/901/expertmessage-window-update...

A packet marked "TCP Window Update" simply indicates that the sender's TCP receive buffer space has increased. Look at the previous packet from the sender - note the Window Size value in the TCP header. Then look at the "TCP Window Update" packet's Window Size setting.

What triggers these "TCP Window Update" packets? When an application picks up data from the receive buffer there is now more receive buffer space available. Wireshark sees the Window Size field value has increased and marks it to let you know the Window Size field has increased.

This is normal network behavior. Problem behaviors would be Zero Window conditions.

Hope that helps!
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Author Comment

by:Dragon0x40
ID: 36539392
In the experts infos:

I have no errors

I have these warnings:

Window is full   20

Zero Window   17

ACKed lost segment (common at capture start)  63

Previous segment los (common st caputre start)  78

Out-Of-Order segment   187

Fast retransmission (suspected)  14

This was on a 1gb ftp file transfer
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LVL 6

Expert Comment

by:netjgrnaut
ID: 36539494
Is this a new question?

Wireshark is not mis-identifying your FTP traffic.
The Window Update packet has nothing to do with MS Windows Update.

So... what's the question?
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Author Comment

by:Dragon0x40
ID: 36539527
I will open a new question.
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