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    SubjectRe: TCP Delayed ACK in FIN/ACK
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    On Sat, Aug 4, 2012 at 4:45 PM, Sławek Janecki <janecki@gmail.com> wrote:
    > I have a node.js client (10.177.62.7) requesting some data from http
    > rest service from server (10.177.0.1).
    > Client is simply using nodejs http.request() method (agent=false).
    > Client is on Ubuntu 11.10 box.
    > Why client sends FIN ACK after 475ms? Why so slow? He should send FIN
    > ACK immediately.
    > I have many situations like this. About 1% of whole traffic is request
    > with delayed FIN ACK.
    > Cpu idle on the client is about 99%, so nothing is draining CPU.
    > How to debug this? What could it be? Is there any sysctl option I need to tune?
    > I think this behaviour is the Delayed ACK feature of RFC1122 TCP stack.
    >
    > Link to tcpdump picture (done on a client machine) :
    > http://i48.tinypic.com/35cpogx.png
    >
    > Can you tell why kernel delayed that FIN/ACK.
    > In tcpflow data there is exacly one ACK per packet comming from server.
    > Why kernel delayed client FIN/ACK.
    > It could avoid sending ACK every 'data' packet.
    > But it choose to delay FIN/ACK?
    > Is this possible? Is this a bug?
    >
    > I've also posted question on stackexchange:
    > http://stackoverflow.com/questions/11711218/client-sends-delayed-fin-ack-500ms-to-server
    >
    > Please help.

    CC'ing netdev.

    --
    Thanks,
    //richard
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