Bandwidth & Performance

Discussion in 'Linux Networking' started by Martin Greco, Aug 20, 2003.

  1. Martin Greco

    Martin Greco Guest

    Hi everyone

    I have a RedHat 8 Box as gateway for about 15 clients through NAT. The
    connection is a 256Kb DSL over pptp.
    the situation is this: when eth1 (which is the internal NIC) is down I have
    about 26 KB downstream and 12 KB upstream in several tests, but when it is
    up and there are many clients operating the performance goes down, that's it
    5 or 10 KB downstram and 3KB or 4KB upstream.

    Could this be possible? is it a configuration issue or a problem with the

    Thanks in advance
    Martin Greco, Aug 20, 2003
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  2. Very possible. This is due to the nature of all internet links where TCP
    traffic particularly is involved. With TCP, the client machines send
    ACKnowledgement packets to tell the server it received the data fine and in
    order. If the bandwidth is saturated in the opposite direction then these
    ACK packets get lost due to conjestion.

    The blind way to solve this is more bandwidth, the clever way Linux folk fix
    it is with Quality of Service (QoS for short). What this does is 'shape' the
    traffic and prioritizes the packets so that the packets which need low
    latency (e.g. SSH) leave as quickly as possible whilst 'bulk' traffic (e.g.
    FTP and file sharing software) is used as filler.

    A good place to learn are read up on this is - Advanced-Routing-HOWTO

    you can also look at my website and my script as a solution to the problem in
    good GPL fashion. Its a script that can be dropped in and should not effect
    anything thats already in place on the firewall.


    Alexander Clouter, Sep 2, 2003
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