Re: suffering from poor network performance...

From: Charles Swiger (cswiger_at_mac.com)
Date: 12/17/03

  • Next message: Kevin Stevens: "Re: suffering from poor network performance..." 
    Date: Tue, 16 Dec 2003 20:32:20 -0500
To: Alex <xela@battleface.com>(ander Sendzimir)

    On Dec 16, 2003, at 7:22 PM, Alex (ander Sendzimir) wrote:
    [ ... ]

    First, Barney was correct: using "ping -f" will run into the ICMP
    response limitation. Try using "ping -i 0.01 _hostname_", instead, and
    you may find out that you don't have a problem with packet loss at all
    at this lower speed.

    > What does power cycling the hub do in this case (Netgear DS108)?
    > Finally, what is the difference between half and full duplex?

    Half-duplex means the interface can either send or receive, but not do
    both at the same time. Full-duplex requires a switch.

    [ ... ]
    >> It is sold as a hub. Most of these "dual-speed" hubs are/were two
    >> hubs,
    >> one of each speed, with a two-port internal switch connecting them.
    >> The
    >> physical ports would auto-join to whichever side the connection speed
    >> indicated. Infuriating to use as tap devices, if you ended up on the
    >> wrong side of the switch from your target, you wouldn't see any
    >> broadcast
    >> traffic. ;)
    >
    > Interesting. I didn't know that. What is the difference between a
    > switch and a hub? I thought I understood. Perhaps this is not the
    > case. Thanks.

    Hubs are dumb; typically all ports share a single wire-speed chunk of
    bandwidth, they do not regenerate packets and are subject to
    significant topology constraints (you can't nest or "tree" them more
    than about two levels deep).

    Switches are smarter and often have external management interfaces,
    they keep track of each port individually in terms of speed and duplex
    (ie, permit full-duplex operation), they keep track of MAC addresses
    via their own ARP tables and only forward traffic to the destination
    port(s) to which the traffic should go. Switches generally have a
    store-and-forward mechanism for handling packets so that they eliminate
    collisions and drop errors at the sending port rather than forwarding
    broken traffic to all listeners the way a hub does, thereby
    regenerating packet timing and permitting much larger topologies.
    Switches may implement spanning tree to prevent loops, and often handle
    things like VLAN tagging and port aggregration or trunking for
    switch-to-switch connections.

    Switches support internal bandwidth many times greater than indidivual
    port wirespeed so that many machines can be sending traffic at "full
    speed". Two machines talking to each other at "full speed" will
    saturate a hub; if four machines all want to talk on a hub, they each
    get a fraction of the bandwidth. 

    -- 
-Chuck
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  • Next message: Kevin Stevens: "Re: suffering from poor network performance..."

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