ssh server waits for an ACK from the client

From: Greg Kempe (
Date: 05/24/05

  • Next message: Leandro Costa: "Re: SFTP between Linux and Windows"
    Date: Tue, 24 May 2005 11:25:04 -0700


    I have noticed that a large amount of data moving from an ssh server
    to the client pauses occasionally pending a packet from the client.
    Very simply, I ssh into a remote server and 'cat' a large file (~6
    MB). If I grab the data on the server-client path and prevent it from
    reaching the client, the server stops sending after a while. If I pass
    the grabbed data on to the client, it reads it and sends a small
    packet back to the server, which then starts sending again.

    This is not at the TCP level so I know it isn't a TCP ACK issue. I
    very much doubt it's an issue with 'cat', either. Does ssh wait for an
    application-level ACK every few thousand bytes before continuing to
    send data?

    I am using OpenSSH_4.0p1, OpenSSL 0.9.7g 11 Apr 2005 on cygwin,
    Windows XP sp2. I have had the same results using the same client and
    an ssh server on Linux with OpenSSH_3.8p1, SSH protocols 1.5/2.0,
    OpenSSL 0.9.7d 17 Mar 2004



  • Next message: Leandro Costa: "Re: SFTP between Linux and Windows"

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