Strange problem with FTP (too many connections stop connecting) - Networking

This is a discussion on Strange problem with FTP (too many connections stop connecting) - Networking ; I have a certain process (mine) that sends a lot of queries to a FTP server (also mine). All machines and processes are mine and there is no foul play involved. The machines are on the same organizational network, though ...

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Thread: Strange problem with FTP (too many connections stop connecting)

  1. Strange problem with FTP (too many connections stop connecting)

    I have a certain process (mine) that sends a lot of queries to a FTP
    server (also mine). All machines and processes are mine and there is
    no foul play involved. The machines are on the same organizational
    network, though on different subnets.

    The server is vsftpd on debian.

    The client is a perl script using Net::FTP perl module running on
    ubuntu gutsy.

    As part of the process, the client connects to FTP daemon and does a
    lot of directory listings. (like thousands of queries) as the client
    browses through the server's directory tree.

    That's all good and well.

    As you know, FTP is such a protocol that for every directory listing, a
    new data connection is made, with direction depending on passive
    vs. active mode.

    The problem is that sporadically, the connections that the client
    makes to the server, time out in the "connect()" call. In other words,
    the server is listening (and I can telnet to the specific port
    assigned by FTP from another machine), but the client times out.

    The weird thing is this: if I type

    telnet

    from the client machine, it times out.

    If I type the same from another machine, it connects (with FTP server
    properly detecting a fake connection coming from another IP and
    discarding that connection).

    My question is WTF, why would connect() calls time out like this.

    Any idea.

    thanks

    i

  2. Re: Strange problem with FTP (too many connections stop connecting)

    On 2008-01-04, Ignoramus17950 wrote:
    > I have a certain process (mine) that sends a lot of queries to a FTP
    > server (also mine). All machines and processes are mine and there is
    > no foul play involved. The machines are on the same organizational
    > network, though on different subnets.
    >
    > The server is vsftpd on debian.
    >
    > The client is a perl script using Net::FTP perl module running on
    > ubuntu gutsy.
    >
    > As part of the process, the client connects to FTP daemon and does a
    > lot of directory listings. (like thousands of queries) as the client
    > browses through the server's directory tree.
    >
    > That's all good and well.
    >
    > As you know, FTP is such a protocol that for every directory listing, a
    > new data connection is made, with direction depending on passive
    > vs. active mode.
    >
    > The problem is that sporadically, the connections that the client
    > makes to the server, time out in the "connect()" call. In other words,
    > the server is listening (and I can telnet to the specific port
    > assigned by FTP from another machine), but the client times out.
    >
    > The weird thing is this: if I type
    >
    > telnet
    >
    > from the client machine, it times out.
    >
    > If I type the same from another machine, it connects (with FTP server
    > properly detecting a fake connection coming from another IP and
    > discarding that connection).
    >
    > My question is WTF, why would connect() calls time out like this.


    Oh yeah, and netstat -t shows

    tcp 0 1 :57013 :38786 SYN_SENT

    client and server names suppressed for privacy.

    i

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