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FTP over PPP stalls out - Linux Setup, Configuration & Administration

Maybe somebody else has experienced similar problems and can make suggestions that pertain to what is happening to me. I was running Mandrake 9. The system basically performed flawlessly. I was able to PPP with a modem from the linux box, ftp over that connection, as well as set up the linux box to be an IPTABLES NAT so that workstations on the network could have Internet connectivity as well. The modem line was a backup to the Cable Modem interface, which also worked well under Mandrake. I recently installed RH9 on this pc. I did this because I bought ...

  1. #1

    Default FTP over PPP stalls out

    Maybe somebody else has experienced similar problems and can make
    suggestions that pertain to what is happening to me.

    I was running Mandrake 9. The system basically performed flawlessly.
    I was able to PPP with a modem from the linux box, ftp over that
    connection, as well as set up the linux box to be an IPTABLES NAT so
    that workstations on the network could have Internet connectivity as
    well. The modem line was a backup to the Cable Modem interface, which
    also worked well under Mandrake.

    I recently installed RH9 on this pc. I did this because I bought a
    new RAID5 controller (S150SX4) from promise and it has specific kernel
    requirements- one of them being 2.4.20-8 or 2.4.20-8smp. The
    controller card is working fine and performance is acceptable.

    Here is the problem:
    PPP is performing poorly. There are 10 - 20% RX errors as well as 10
    - 20% packet loss with simple pings.

    This very same modem and phoneline when plugged into a system running
    Windows XP performs fine.

    This very same modem and phoneline also performed fine with the
    previous Mandrake configuration .

    Regardless of connect speeds which are either 28800 or 49333,
    depending on whether or not I enable V90, I get 1.4 - 1.6KB/sec avg
    speed over FTP. Note: this is a USR Courier V.everything modem.

    I used to get over 4k on average with bursts of 5-6KB/sec.

    With the packet loss and RX errors, needless to say, this PPP
    interface is worthless as a NAT.

    Here is my system:
    Dual P2 400's. (Not a powerhouse, but it has been reliable for a
    couple years now)
    1GB pc-133 RAM
    400GB RAID5
    Intel Gigabit Ethernet
    3Com 10/100 Ethernet
    Adaptec 2940 w/Tandberg SLR5 tapedrive and NEC Cd-Rom
    Panasonic IDE Cd-Rom
    USR Courier v.everything modem

    RH9
    kernel-2.4.20-8smp
    iptables v1.2.7a

    So far I have tried:
    connecting to a different ISP
    using a different modem
    lowering baud rates and line speeds
    verified correct modem init string
    asyncmap 0

    None of this made much of a difference if at all.

    During FTP transfers, both CPUs are virtually idle. 2-3% intermittent
    utilization and yet the ftp performance is poor.

    I tried using mru 576 and mtu 576 and there was a slight throughput
    improvement. 1.9KB/sec, but nothing great. Packet loss and RX errors
    still were at 10-20%.

    Also, with mru and mtu at 576, workstations fail to transfer through
    the NAT. It seems that the minimum that works over the NAT is 1500.

    Can somebody suggest some things to test to help narrow down this
    problem?

    Thanks in advance,
    Charles
    2boxers_at_comcast_dot_net Guest

  2. #2

    Default Re: FTP over PPP stalls out

    2boxers_at_comcast_dot_net wrote: 

    Here are some comments / suggestions:

    *) Various people have reported poor performance issues with various FTP
    programs (clients and/or servers) on various releases of <pick your
    favorite Linux distro>. So you might want to run some "Google Groups"
    searches on the Linux/Redhat newsgroups using keywords like "poor ftp
    performance" to see if you can locate some of these message threads.
    (
    http://www.google.com/advanced_group_search
    Newsgroups: *linux* *redhat*
    )

    *) Even though the manufacturer of your RAID5 controller states that the
    "required" kernel version as '2.4.20-8', chances are that other kernel
    versions - and particularly later kernel versions - will work as good
    as, or even better than, the 2.4.20-8 release.

    *) Multiple RH9 Linux 'kernel' RPMs can be installed on a single system
    at the same time, giving you the option to boot the computer into one of
    several different kernel versions. So you might consider downloading and
    installing the latest 'update' release of the RH9 'kernel' RPM.
    (ftp://ftp.redhat.com/pub/redhat/linux/updates/9/en/os)

    *) The Linux kernels that Red Hat provides contain Red Hat-specific
    "fixes" in the kernel code. So you might want to try downloading,
    building, and installing a stock Linux 2.4.20 (or later) kernel - i.e.,
    a kernel that hasn't been "fixed" by Red Hat - to see if a stock kernel
    works better. (http://www.kernel.org)

    *) The 'netfilter' firewall software (in the Linux kernel) has some
    kernel modules that provide protocol-specific support for connection
    tracking (ip_conntrack_*) and NAT (ip_nat_*). FTP is one of the
    protocols that requires these special connection tracking and NAT kernel
    modules - i.e., 'ip_conntrack_ftp' and 'ip_nat_ftp', respectively.

    [root]# modprobe ip_conntrack_ftp
    [root]# modprobe ip_nat_ftp
    [root]# lsmod | grep ^ip | sort
    [root]# find /lib/modules/ -name "ip_conntrack*"
    [root]# find /lib/modules/ -name "ip_nat_*"

    *) Are you using the latest-and-greatest release of the 'ppp' RPM? FWIW,
    here's the version that's currently installed on my RH9 Linux box:

    [root]# rpm -q ppp
    ppp-2.4.1-10

    (n.b. I don't use PPP. So I can't offer any advice as to whether this is
    a stable/good release of the 'ppp' RPM or not.)

    FWIW, if the 'Fedora Core 1' distro has a newer version/release of the
    'ppp' RPM, you might consider downloading and then building the *SOURCE*
    RPM (SRPM) (.src.rpm) for the new release. You should be able to find
    the 'ppp' SRPM on Red Hat's FTP site (which seems to be off line today,
    along with Red Hat's web server <?>).

    --
    Jim

    To reply by email, remove "link" and change "now.here" to "yahoo"
    jfischer_link5809{at}now.here.com


    Jim Guest

  3. #3

    Default Re: FTP over PPP stalls out

    On Fri, 14 Nov 2003 12:55:00 -0600, Jim Fischer
    <here.com> wrote:
     

    I have been doing this for the past few days. My problem is most
    noticeable using FTP since FTP uses all available bandwidth, but a
    simple ping also reveals the 10-20% packet loss, so an FTP specific
    solution may not be in order. I could have picked a better subject
    header, but it seems that many people are having this problem with
    redhat 9.
     

    You would think so.

    Actually, this device has very specific kernel support, unfortunately.
    There has been talk of a partial source release of the driver which
    would allow building the driver as a module or as part of a kernel,
    but as of now, the driver is installed, prebuilt for specific kernels
    only. This is a growing concern as there may be reasons that require
    building a new kernel.

    http://www.promise.com/support/download/download2_eng.asp?productId=112&category=All&os=10 0

    Promise really needs to get on the ball with Linux support.
     

    Yes I know, I had 8 or 9 or so on my Mandrake system, Long live
    lilo... but this doesnt help me in this case unless there are options
    that I need to add or remove from my existing kernel version to fix
    ppp.
     

    I would much rather use a plain vanilla kernel, but as of right now I
    don't have the choice as explained above.

    This is liable to be the fix, but unfortunately I cannot employ this
    since the controller driver is forcing me to use a specific kernel.

    I know better than to buy another one of these controllers for this
    reason, but for now, all seems to be working well with the controller
    itself and I need the storage capacity it is providing.
     

    I have never had to use the protocol specific modules before, but I do
    not question you. I know they are there for a reason.

    Additionally, I have the problem without iptables loaded. In other
    words, PPP only from the linux box, ftp client from the linux box over
    that ppp connection produces the poor performance.
     

    This is what I have installed.
     

    Building the latest PPP may not be a bad idea. It wouldnt be the
    first time I have fixed smp related problems by building new binaries.

    Any idea if pppd has any smp specific support or properties?

    If this were a kernel specific problem, what methods are there for
    diagnosing poor ppp performance aside from replacing the kernel?

    How can I check if the IRQ's are being serviced properly?

    How can I check if the pppd process is being serviced properly?

    Charles
    2boxers_at_comcast_dot_net Guest

  4. #4

    Default Re: FTP over PPP stalls out

    no name wrote:
     

    Maybe your com port is getting serial overruns because the new card is
    causing lots of higher priority interrupts.

    I used to be able to make any ppp on com grind to a halt by scp-ing
    from/flood pinging my gateway - doesn't happen now I've got a PCI DSL modem
    on the same set up. I didn't fix it, but assumed it was because the IRQ on
    the com was too low.

    You can change this with irqtune.

    Andy.


    Andy Guest

  5. #5

    Default Re: FTP over PPP stalls out

    >Maybe your com port is getting serial overruns because the new card is 
    Does this even work with 2.4.x SMP kernels with APIC enabled?
    Charles
    2boxers_at_comcast_dot_net Guest

  6. #6

    Default Re: FTP over PPP stalls out

    no name wrote:
     
    > Does this even work with 2.4.x SMP kernels with APIC enabled?
    > Charles[/ref]

    I haven't got a clue, if it were me I would just try and see - but then you
    may have more to loose if it all goes pear shaped :-)

    Andy.

    Andy Guest

  7. #7

    Default Re: FTP over PPP stalls out

    Problem Solved !!!

    I shut off the irqbalance service.

    I adjusted the IRQ affinity for the serial port that the PPP modem was
    connected to.

    echo 2 > /proc/irq/4/smp_affinity

    more about it here:
    http://www.spoonix.com/howtos/smp_affinity.txt

    When I did this, I immediately noticed a dramatic change for the
    better.

    By moving IRQ 4 to the second CPU, the performance was restored to
    PPP.

    I really dont know if it was IRQ contention or load on CPU 1, but even
    with all the nics and controllers on CPU 2 with the serial port, the
    performance increase was noticeable.

    For good measure, I put everything but that serial port on CPU 1. Of
    course individual processes can still interrupt either processor, but
    it seems like it is fixed now.

    RX errors are down to about 2% from 20%.
    Downloads are up to 5.8 KB/sec from 1.5 KB/sec.

    I notice in this configuration about 10% more CPU load to the second
    processor and I take that as a good thing.

    Additionally, something I didn't even have in my old configuration was
    disabling MNP5 compression. This was a minor gain, but nevertheless
    when we are talking kilobytes, I'll take what I can get.

    Charles
    2boxers_at_comcast_dot_net Guest

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