Re: What is the expected response to Window Probe packets

From: LDB
Date: Tue Apr 14 2009 - 20:33:36 EST


Satish Chandra Kilaru wrote:
> Hi
>
> What is the expected behavior when Linux machine receives zero-window
> probe packets? RFC says receiving client should respond with current
> window size.
>
> Does this mean that client MUST respond with a window update (if the
> window size is still 0, say that it is 0, else give the current window
> size.). Can client not responding to a window probe be considered as a
> bug in Client's TCP/IP stack?
>
> Thanks in advance
> --Satish
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>

If a receiving client cannot handle anymore data for whatever reason,
then the client then sets the response packet's TCP window size to 0.
The server sending the packets, then should back-off accordingly - the
elegance behind the "back-off" depends on your NIC settings and switch
settings as well, this is called flow control.

If the current window size is 0, then the client will respond with
0, back to the sending server.

Yes, the client must respond with an ACK to the sending server with
the current window size. If the window size is 0 for the receiving
client, then the sending server will keep trying at intervals of x
seconds.

A client not responding to the probes, could be a sign of the client
being too busy to respond to ACKs.

I guess there could be a bug, but depends on your situation and customizations.
I am willing to bet there is something else wrong though.

Thanks ..

LDB

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